src/com/android/launcher3/PagedView.java

/*
 * Copyright (C) 2012 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.launcher3;

import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.animation.AnimatorSet;
import android.animation.ObjectAnimator;
import android.animation.TimeInterpolator;
import android.animation.ValueAnimator;
import android.animation.ValueAnimator.AnimatorUpdateListener;
import android.content.Context;
import android.content.res.Resources;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.graphics.Rect;
import android.os.Bundle;
import android.os.Parcel;
import android.os.Parcelable;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.InputDevice;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.ViewParent;
import android.view.ViewGroup.LayoutParams;
import android.view.accessibility.AccessibilityEvent;
import android.view.accessibility.AccessibilityManager;
import android.view.accessibility.AccessibilityNodeInfo;
import android.view.animation.AnimationUtils;
import android.view.animation.DecelerateInterpolator;
import android.view.animation.Interpolator;
import android.view.animation.LinearInterpolator;
import android.widget.FrameLayout;
import android.widget.Scroller;

import java.util.ArrayList;

/**
 * An abstraction of the original Workspace which supports browsing through a
 * sequential list of "pages"
 */
public abstract class PagedView extends ViewGroup implements ViewGroup.OnHierarchyChangeListener {
    private static final String TAG = "PagedView";
    private static final boolean DEBUG = false;
    protected static final int INVALID_PAGE = -1;

    // the min drag distance for a fling to register, to prevent random page shifts
    private static final int MIN_LENGTH_FOR_FLING = 25;

    protected static final int PAGE_SNAP_ANIMATION_DURATION = 750;
    protected static final int SLOW_PAGE_SNAP_ANIMATION_DURATION = 950;
    protected static final float NANOTIME_DIV = 1000000000.0f;

    private static final float OVERSCROLL_ACCELERATE_FACTOR = 2;
    private static final float OVERSCROLL_DAMP_FACTOR = 0.14f;

    private static final float RETURN_TO_ORIGINAL_PAGE_THRESHOLD = 0.33f;
    // The page is moved more than halfway, automatically move to the next page on touch up.
    private static final float SIGNIFICANT_MOVE_THRESHOLD = 0.4f;

    // The following constants need to be scaled based on density. The scaled versions will be
    // assigned to the corresponding member variables below.
    private static final int FLING_THRESHOLD_VELOCITY = 500;
    private static final int MIN_SNAP_VELOCITY = 1500;
    private static final int MIN_FLING_VELOCITY = 250;

    // We are disabling touch interaction of the widget region for factory ROM.
    private static final boolean DISABLE_TOUCH_INTERACTION = false;
    private static final boolean DISABLE_TOUCH_SIDE_PAGES = false;
    private static final boolean DISABLE_FLING_TO_DELETE = true;

    static final int AUTOMATIC_PAGE_SPACING = -1;

    protected int mFlingThresholdVelocity;
    protected int mMinFlingVelocity;
    protected int mMinSnapVelocity;

    protected float mDensity;
    protected float mSmoothingTime;
    protected float mTouchX;

    protected boolean mFirstLayout = true;

    protected int mCurrentPage;
    protected int mChildCountOnLastLayout;

    protected int mNextPage = INVALID_PAGE;
    protected int mMaxScrollX;
    protected Scroller mScroller;
    private VelocityTracker mVelocityTracker;

    private float mParentDownMotionX;
    private float mParentDownMotionY;
    private float mDownMotionX;
    private float mDownMotionY;
    private float mDownScrollX;
    protected float mLastMotionX;
    protected float mLastMotionXRemainder;
    protected float mLastMotionY;
    protected float mTotalMotionX;
    private int mLastScreenCenter = -1;
    private int[] mChildOffsets;
    private int[] mChildRelativeOffsets;

    protected final static int TOUCH_STATE_REST = 0;
    protected final static int TOUCH_STATE_SCROLLING = 1;
    protected final static int TOUCH_STATE_PREV_PAGE = 2;
    protected final static int TOUCH_STATE_NEXT_PAGE = 3;
    protected final static int TOUCH_STATE_REORDERING = 4;

    protected final static float ALPHA_QUANTIZE_LEVEL = 0.0001f;

    protected int mTouchState = TOUCH_STATE_REST;
    protected boolean mForceScreenScrolled = false;

    protected OnLongClickListener mLongClickListener;

    protected int mTouchSlop;
    private int mPagingTouchSlop;
    private int mMaximumVelocity;
    protected int mPageSpacing;
    protected int mPageLayoutPaddingTop;
    protected int mPageLayoutPaddingBottom;
    protected int mPageLayoutPaddingLeft;
    protected int mPageLayoutPaddingRight;
    protected int mPageLayoutWidthGap;
    protected int mPageLayoutHeightGap;
    protected int mCellCountX = 0;
    protected int mCellCountY = 0;
    protected boolean mCenterPagesVertically;
    protected boolean mAllowOverScroll = true;
    protected int mUnboundedScrollX;
    protected int[] mTempVisiblePagesRange = new int[2];
    protected boolean mForceDrawAllChildrenNextFrame;

    // mOverScrollX is equal to getScrollX() when we're within the normal scroll range. Otherwise
    // it is equal to the scaled overscroll position. We use a separate value so as to prevent
    // the screens from continuing to translate beyond the normal bounds.
    protected int mOverScrollX;

    protected static final int INVALID_POINTER = -1;

    protected int mActivePointerId = INVALID_POINTER;

    private PageSwitchListener mPageSwitchListener;

    protected ArrayList<Boolean> mDirtyPageContent;

    // If true, syncPages and syncPageItems will be called to refresh pages
    protected boolean mContentIsRefreshable = true;

    // If true, modify alpha of neighboring pages as user scrolls left/right
    protected boolean mFadeInAdjacentScreens = false;

    // It true, use a different slop parameter (pagingTouchSlop = 2 * touchSlop) for deciding
    // to switch to a new page
    protected boolean mUsePagingTouchSlop = true;

    // If true, the subclass should directly update scrollX itself in its computeScroll method
    // (SmoothPagedView does this)
    protected boolean mDeferScrollUpdate = false;

    protected boolean mIsPageMoving = false;

    // All syncs and layout passes are deferred until data is ready.
    protected boolean mIsDataReady = false;

    protected boolean mAllowLongPress = true;

    // Page Indicator
    private int mPageIndicatorViewId;
    private PageIndicator mPageIndicator;

    // The viewport whether the pages are to be contained (the actual view may be larger than the
    // viewport)
    private Rect mViewport = new Rect();

    // Reordering
    // We use the min scale to determine how much to expand the actually PagedView measured
    // dimensions such that when we are zoomed out, the view is not clipped
    private int REORDERING_DROP_REPOSITION_DURATION = 200;
    protected int REORDERING_REORDER_REPOSITION_DURATION = 300;
    protected int REORDERING_ZOOM_IN_OUT_DURATION = 250;
    private int REORDERING_SIDE_PAGE_HOVER_TIMEOUT = 300;
    private float REORDERING_SIDE_PAGE_BUFFER_PERCENTAGE = 0.1f;
    private long REORDERING_DELETE_DROP_TARGET_FADE_DURATION = 150;
    private float mMinScale = 1f;
    protected View mDragView;
    protected AnimatorSet mZoomInOutAnim;
    private Runnable mSidePageHoverRunnable;
    private int mSidePageHoverIndex = -1;
    // This variable's scope is only for the duration of startReordering() and endReordering()
    private boolean mReorderingStarted = false;
    // This variable's scope is for the duration of startReordering() and after the zoomIn()
    // animation after endReordering()
    private boolean mIsReordering;
    // The runnable that settles the page after snapToPage and animateDragViewToOriginalPosition
    private int NUM_ANIMATIONS_RUNNING_BEFORE_ZOOM_OUT = 2;
    private int mPostReorderingPreZoomInRemainingAnimationCount;
    private Runnable mPostReorderingPreZoomInRunnable;

    // Edge swiping
    private boolean mOnlyAllowEdgeSwipes = false;
    private boolean mDownEventOnEdge = false;
    private int mEdgeSwipeRegionSize = 0;

    // Convenience/caching
    private Matrix mTmpInvMatrix = new Matrix();
    private float[] mTmpPoint = new float[2];
    private Rect mTmpRect = new Rect();
    private Rect mAltTmpRect = new Rect();

    // Fling to delete
    private int FLING_TO_DELETE_FADE_OUT_DURATION = 350;
    private float FLING_TO_DELETE_FRICTION = 0.035f;
    // The degrees specifies how much deviation from the up vector to still consider a fling "up"
    private float FLING_TO_DELETE_MAX_FLING_DEGREES = 65f;
    protected int mFlingToDeleteThresholdVelocity = -1400;
    // Drag to delete
    private boolean mDeferringForDelete = false;
    private int DELETE_SLIDE_IN_SIDE_PAGE_DURATION = 250;
    private int DRAG_TO_DELETE_FADE_OUT_DURATION = 350;

    // Drop to delete
    private View mDeleteDropTarget;

    private boolean mAutoComputePageSpacing = false;
    private boolean mRecomputePageSpacing = false;

    // Bouncer
    private boolean mTopAlignPageWhenShrinkingForBouncer = false;

    public interface PageSwitchListener {
        void onPageSwitch(View newPage, int newPageIndex);
    }

    public PagedView(Context context) {
        this(context, null);
    }

    public PagedView(Context context, AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public PagedView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        TypedArray a = context.obtainStyledAttributes(attrs,
                R.styleable.PagedView, defStyle, 0);
        setPageSpacing(a.getDimensionPixelSize(R.styleable.PagedView_pageSpacing, 0));
        if (mPageSpacing < 0) {
            mAutoComputePageSpacing = mRecomputePageSpacing = true;
        }
        mPageLayoutPaddingTop = a.getDimensionPixelSize(
                R.styleable.PagedView_pageLayoutPaddingTop, 0);
        mPageLayoutPaddingBottom = a.getDimensionPixelSize(
                R.styleable.PagedView_pageLayoutPaddingBottom, 0);
        mPageLayoutPaddingLeft = a.getDimensionPixelSize(
                R.styleable.PagedView_pageLayoutPaddingLeft, 0);
        mPageLayoutPaddingRight = a.getDimensionPixelSize(
                R.styleable.PagedView_pageLayoutPaddingRight, 0);
        mPageLayoutWidthGap = a.getDimensionPixelSize(
                R.styleable.PagedView_pageLayoutWidthGap, 0);
        mPageLayoutHeightGap = a.getDimensionPixelSize(
                R.styleable.PagedView_pageLayoutHeightGap, 0);
        mPageIndicatorViewId = a.getResourceId(R.styleable.PagedView_pageIndicator, -1);
        a.recycle();

        setHapticFeedbackEnabled(false);
        init();
    }

    /**
     * Initializes various states for this workspace.
     */
    protected void init() {
        mDirtyPageContent = new ArrayList<Boolean>();
        mDirtyPageContent.ensureCapacity(32);
        mScroller = new Scroller(getContext(), new ScrollInterpolator());
        mCurrentPage = 0;
        mCenterPagesVertically = true;

        final ViewConfiguration configuration = ViewConfiguration.get(getContext());
        mTouchSlop = configuration.getScaledPagingTouchSlop();
        mPagingTouchSlop = configuration.getScaledPagingTouchSlop();
        mMaximumVelocity = configuration.getScaledMaximumFlingVelocity();
        mDensity = getResources().getDisplayMetrics().density;

        // Scale the fling-to-delete threshold by the density
        mFlingToDeleteThresholdVelocity =
                (int) (mFlingToDeleteThresholdVelocity * mDensity);

        mFlingThresholdVelocity = (int) (FLING_THRESHOLD_VELOCITY * mDensity);
        mMinFlingVelocity = (int) (MIN_FLING_VELOCITY * mDensity);
        mMinSnapVelocity = (int) (MIN_SNAP_VELOCITY * mDensity);
        setOnHierarchyChangeListener(this);
    }

    protected void onAttachedToWindow() {
        // Hook up the page indicator
        ViewGroup parent = (ViewGroup) getParent();
        if (mPageIndicator == null && mPageIndicatorViewId > -1) {
            mPageIndicator = (PageIndicator) parent.findViewById(mPageIndicatorViewId);
            mPageIndicator.removeAllMarkers();
            mPageIndicator.addMarkers(getChildCount());
        }
    }

    protected void onDetachedFromWindow() {
        // Unhook the page indicator
        mPageIndicator = null;
    }

    void setDeleteDropTarget(View v) {
        mDeleteDropTarget = v;
    }

    // Convenience methods to map points from self to parent and vice versa
    float[] mapPointFromViewToParent(View v, float x, float y) {
        mTmpPoint[0] = x;
        mTmpPoint[1] = y;
        v.getMatrix().mapPoints(mTmpPoint);
        mTmpPoint[0] += v.getLeft();
        mTmpPoint[1] += v.getTop();
        return mTmpPoint;
    }
    float[] mapPointFromParentToView(View v, float x, float y) {
        mTmpPoint[0] = x - v.getLeft();
        mTmpPoint[1] = y - v.getTop();
        v.getMatrix().invert(mTmpInvMatrix);
        mTmpInvMatrix.mapPoints(mTmpPoint);
        return mTmpPoint;
    }

    void updateDragViewTranslationDuringDrag() {
        float x = mLastMotionX - mDownMotionX + getScrollX() - mDownScrollX;
        float y = mLastMotionY - mDownMotionY;
        mDragView.setTranslationX(x);
        mDragView.setTranslationY(y);

        if (DEBUG) Log.d(TAG, "PagedView.updateDragViewTranslationDuringDrag(): " + x + ", " + y);
    }

    public void setMinScale(float f) {
        mMinScale = f;
        requestLayout();
    }

    @Override
    public void setScaleX(float scaleX) {
        super.setScaleX(scaleX);
        if (isReordering(true)) {
            float[] p = mapPointFromParentToView(this, mParentDownMotionX, mParentDownMotionY);
            mLastMotionX = p[0];
            mLastMotionY = p[1];
            updateDragViewTranslationDuringDrag();
        }
    }

    // Convenience methods to get the actual width/height of the PagedView (since it is measured
    // to be larger to account for the minimum possible scale)
    int getViewportWidth() {
        return mViewport.width();
    }
    int getViewportHeight() {
        return mViewport.height();
    }

    // Convenience methods to get the offset ASSUMING that we are centering the pages in the
    // PagedView both horizontally and vertically
    int getViewportOffsetX() {
        return (getMeasuredWidth() - getViewportWidth()) / 2;
    }

    int getViewportOffsetY() {
        return (getMeasuredHeight() - getViewportHeight()) / 2;
    }

    public void setPageSwitchListener(PageSwitchListener pageSwitchListener) {
        mPageSwitchListener = pageSwitchListener;
        if (mPageSwitchListener != null) {
            mPageSwitchListener.onPageSwitch(getPageAt(mCurrentPage), mCurrentPage);
        }
    }

    /**
     * Note: this is a reimplementation of View.isLayoutRtl() since that is currently hidden api.
     */
    public boolean isLayoutRtl() {
        return (getLayoutDirection() == LAYOUT_DIRECTION_RTL);
    }

    /**
     * Called by subclasses to mark that data is ready, and that we can begin loading and laying
     * out pages.
     */
    protected void setDataIsReady() {
        mIsDataReady = true;
    }

    protected boolean isDataReady() {
        return mIsDataReady;
    }

    /**
     * Returns the index of the currently displayed page.
     *
     * @return The index of the currently displayed page.
     */
    int getCurrentPage() {
        return mCurrentPage;
    }

    int getNextPage() {
        return (mNextPage != INVALID_PAGE) ? mNextPage : mCurrentPage;
    }

    int getPageCount() {
        return getChildCount();
    }

    View getPageAt(int index) {
        return getChildAt(index);
    }

    protected int indexToPage(int index) {
        return index;
    }

    /**
     * Updates the scroll of the current page immediately to its final scroll position.  We use this
     * in CustomizePagedView to allow tabs to share the same PagedView while resetting the scroll of
     * the previous tab page.
     */
    protected void updateCurrentPageScroll() {
        // If the current page is invalid, just reset the scroll position to zero
        int newX = 0;
        if (0 <= mCurrentPage && mCurrentPage < getPageCount()) {
            int offset = getChildOffset(mCurrentPage);
            int relOffset = getRelativeChildOffset(mCurrentPage);
            newX = offset - relOffset;
        }
        scrollTo(newX, 0);
        mScroller.setFinalX(newX);
        mScroller.forceFinished(true);
    }

    /**
     * Called during AllApps/Home transitions to avoid unnecessary work. When that other animation
     * ends, {@link #resumeScrolling()} should be called, along with
     * {@link #updateCurrentPageScroll()} to correctly set the final state and re-enable scrolling.
     */
    void pauseScrolling() {
        mScroller.forceFinished(true);
    }

    /**
     * Enables scrolling again.
     * @see #pauseScrolling()
     */
    void resumeScrolling() {
    }
    /**
     * Sets the current page.
     */
    void setCurrentPage(int currentPage) {
        if (!mScroller.isFinished()) {
            mScroller.abortAnimation();
        }
        // don't introduce any checks like mCurrentPage == currentPage here-- if we change the
        // the default
        if (getChildCount() == 0) {
            return;
        }

        mForceScreenScrolled = true;
        mCurrentPage = Math.max(0, Math.min(currentPage, getPageCount() - 1));
        updateCurrentPageScroll();
        notifyPageSwitchListener();
        invalidate();
    }

    protected void notifyPageSwitchListener() {
        if (mPageSwitchListener != null) {
            mPageSwitchListener.onPageSwitch(getPageAt(mCurrentPage), mCurrentPage);
        }

        // Update the page indicator (when we aren't reordering)
        if (mPageIndicator != null && !isReordering(false)) {
            mPageIndicator.setActiveMarker(getNextPage());
        }
    }
    protected void pageBeginMoving() {
        if (!mIsPageMoving) {
            mIsPageMoving = true;
            onPageBeginMoving();
        }
    }

    protected void pageEndMoving() {
        if (mIsPageMoving) {
            mIsPageMoving = false;
            onPageEndMoving();
        }
    }

    protected boolean isPageMoving() {
        return mIsPageMoving;
    }

    // a method that subclasses can override to add behavior
    protected void onPageBeginMoving() {
    }

    // a method that subclasses can override to add behavior
    protected void onPageEndMoving() {
    }

    /**
     * Registers the specified listener on each page contained in this workspace.
     *
     * @param l The listener used to respond to long clicks.
     */
    @Override
    public void setOnLongClickListener(OnLongClickListener l) {
        mLongClickListener = l;
        final int count = getPageCount();
        for (int i = 0; i < count; i++) {
            getPageAt(i).setOnLongClickListener(l);
        }
    }

    @Override
    public void scrollBy(int x, int y) {
        scrollTo(mUnboundedScrollX + x, getScrollY() + y);
    }

    @Override
    public void scrollTo(int x, int y) {
        final boolean isRtl = isLayoutRtl();
        mUnboundedScrollX = x;

        boolean isXBeforeFirstPage = isRtl ? (x > mMaxScrollX) : (x < 0);
        boolean isXAfterLastPage = isRtl ? (x < 0) : (x > mMaxScrollX);
        if (isXBeforeFirstPage) {
            super.scrollTo(0, y);
            if (mAllowOverScroll) {
                if (isRtl) {
                    overScroll(x - mMaxScrollX);
                } else {
                    overScroll(x);
                }
            }
        } else if (isXAfterLastPage) {
            super.scrollTo(mMaxScrollX, y);
            if (mAllowOverScroll) {
                if (isRtl) {
                    overScroll(x);
                } else {
                    overScroll(x - mMaxScrollX);
                }
            }
        } else {
            mOverScrollX = x;
            super.scrollTo(x, y);
        }

        mTouchX = x;
        mSmoothingTime = System.nanoTime() / NANOTIME_DIV;

        // Update the last motion events when scrolling
        if (isReordering(true)) {
            float[] p = mapPointFromParentToView(this, mParentDownMotionX, mParentDownMotionY);
            mLastMotionX = p[0];
            mLastMotionY = p[1];
            updateDragViewTranslationDuringDrag();
        }
    }

    // we moved this functionality to a helper function so SmoothPagedView can reuse it
    protected boolean computeScrollHelper() {
        if (mScroller.computeScrollOffset()) {
            // Don't bother scrolling if the page does not need to be moved
            if (getScrollX() != mScroller.getCurrX()
                || getScrollY() != mScroller.getCurrY()
                || mOverScrollX != mScroller.getCurrX()) {
                scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
            }
            invalidate();
            return true;
        } else if (mNextPage != INVALID_PAGE) {
            mCurrentPage = Math.max(0, Math.min(mNextPage, getPageCount() - 1));
            mNextPage = INVALID_PAGE;
            notifyPageSwitchListener();

            // We don't want to trigger a page end moving unless the page has settled
            // and the user has stopped scrolling
            if (mTouchState == TOUCH_STATE_REST) {
                pageEndMoving();
            }

            onPostReorderingAnimationCompleted();
            // Notify the user when the page changes
            AccessibilityManager accessibilityManager = (AccessibilityManager)
                    getContext().getSystemService(Context.ACCESSIBILITY_SERVICE);
            if (accessibilityManager.isEnabled()) {
                AccessibilityEvent ev =
                    AccessibilityEvent.obtain(AccessibilityEvent.TYPE_VIEW_SCROLLED);
                ev.getText().add(getCurrentPageDescription());
                sendAccessibilityEventUnchecked(ev);
            }
            return true;
        }
        return false;
    }

    @Override
    public void computeScroll() {
        computeScrollHelper();
    }

    protected boolean shouldSetTopAlignedPivotForWidget(int childIndex) {
        return mTopAlignPageWhenShrinkingForBouncer;
    }

    public static class LayoutParams extends ViewGroup.LayoutParams {
        public boolean isFullScreenPage = false;

        /**
         * {@inheritDoc}
         */
        public LayoutParams(int width, int height) {
            super(width, height);
        }

        public LayoutParams(ViewGroup.LayoutParams source) {
            super(source);
        }
    }

    protected LayoutParams generateDefaultLayoutParams() {
        return new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT);
    }

    public void addFullScreenPage(View page, int width, int height) {
        LayoutParams lp = generateDefaultLayoutParams();
        lp.isFullScreenPage = true;
        super.addView(page, 0, lp);
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        if (!mIsDataReady || getChildCount() == 0) {
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
            return;
        }

        // We measure the dimensions of the PagedView to be larger than the pages so that when we
        // zoom out (and scale down), the view is still contained in the parent
        int widthMode = MeasureSpec.getMode(widthMeasureSpec);
        int widthSize = MeasureSpec.getSize(widthMeasureSpec);
        int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        int heightSize = MeasureSpec.getSize(heightMeasureSpec);
        // NOTE: We multiply by 1.5f to account for the fact that depending on the offset of the
        // viewport, we can be at most one and a half screens offset once we scale down
        DisplayMetrics dm = getResources().getDisplayMetrics();
        int maxSize = Math.max(dm.widthPixels, dm.heightPixels);
        int parentWidthSize = (int) (1.5f * maxSize);
        int parentHeightSize = maxSize;
        int scaledWidthSize = (int) (parentWidthSize / mMinScale);
        int scaledHeightSize = (int) (parentHeightSize / mMinScale);
        mViewport.set(0, 0, widthSize, heightSize);

        if (widthMode == MeasureSpec.UNSPECIFIED || heightMode == MeasureSpec.UNSPECIFIED) {
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
            return;
        }

        // Return early if we aren't given a proper dimension
        if (widthSize <= 0 || heightSize <= 0) {
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
            return;
        }

        /* Allow the height to be set as WRAP_CONTENT. This allows the particular case
         * of the All apps view on XLarge displays to not take up more space then it needs. Width
         * is still not allowed to be set as WRAP_CONTENT since many parts of the code expect
         * each page to have the same width.
         */
        final int verticalPadding = getPaddingTop() + getPaddingBottom();
        final int horizontalPadding = getPaddingLeft() + getPaddingRight();

        // The children are given the same width and height as the workspace
        // unless they were set to WRAP_CONTENT
        if (DEBUG) Log.d(TAG, "PagedView.onMeasure(): " + widthSize + ", " + heightSize);
        if (DEBUG) Log.d(TAG, "PagedView.scaledSize: " + scaledWidthSize + ", " + scaledHeightSize);
        if (DEBUG) Log.d(TAG, "PagedView.parentSize: " + parentWidthSize + ", " + parentHeightSize);
        if (DEBUG) Log.d(TAG, "PagedView.horizontalPadding: " + horizontalPadding);
        if (DEBUG) Log.d(TAG, "PagedView.verticalPadding: " + verticalPadding);
        final int childCount = getChildCount();
        for (int i = 0; i < childCount; i++) {
            // disallowing padding in paged view (just pass 0)
            final View child = getPageAt(i);
            final LayoutParams lp = (LayoutParams) child.getLayoutParams();

            int childWidthMode;
            int childHeightMode;
            int childWidth;
            int childHeight;

            if (!lp.isFullScreenPage) {
                if (lp.width == LayoutParams.WRAP_CONTENT) {
                    childWidthMode = MeasureSpec.AT_MOST;
                } else {
                    childWidthMode = MeasureSpec.EXACTLY;
                }

                if (lp.height == LayoutParams.WRAP_CONTENT) {
                    childHeightMode = MeasureSpec.AT_MOST;
                } else {
                    childHeightMode = MeasureSpec.EXACTLY;
                }

                childWidth = widthSize - horizontalPadding;
                childHeight = heightSize - verticalPadding;

            } else {
                childWidthMode = MeasureSpec.EXACTLY;
                childHeightMode = MeasureSpec.EXACTLY;

                childWidth = getViewportWidth();
                childHeight = getViewportHeight();
            }

            final int childWidthMeasureSpec =
                    MeasureSpec.makeMeasureSpec(childWidth, childWidthMode);
                final int childHeightMeasureSpec =
                    MeasureSpec.makeMeasureSpec(childHeight, childHeightMode);
            child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
        }
        setMeasuredDimension(scaledWidthSize, scaledHeightSize);

        // We can't call getChildOffset/getRelativeChildOffset until we set the measured dimensions.
        // We also wait until we set the measured dimensions before flushing the cache as well, to
        // ensure that the cache is filled with good values.
        invalidateCachedOffsets();

        if (childCount > 0) {
            if (DEBUG) Log.d(TAG, "getRelativeChildOffset(): " + getViewportWidth() + ", "
                    + getChildWidth(0));

            // Calculate the variable page spacing if necessary
            if (mAutoComputePageSpacing && mRecomputePageSpacing) {
                // The gap between pages in the PagedView should be equal to the gap from the page
                // to the edge of the screen (so it is not visible in the current screen).  To
                // account for unequal padding on each side of the paged view, we take the maximum
                // of the left/right gap and use that as the gap between each page.
                int offset = getRelativeChildOffset(0);
                int spacing = Math.max(offset, widthSize - offset -
                        getChildAt(0).getMeasuredWidth());
                setPageSpacing(spacing);
                mRecomputePageSpacing = false;
            }
        }
    }

    public void setPageSpacing(int pageSpacing) {
        mPageSpacing = pageSpacing;
        invalidateCachedOffsets();
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        if (!mIsDataReady || getChildCount() == 0) {
            return;
        }

        if (DEBUG) Log.d(TAG, "PagedView.onLayout()");
        final int childCount = getChildCount();

        int offsetX = getViewportOffsetX();
        int offsetY = getViewportOffsetY();

        // Update the viewport offsets
        mViewport.offset(offsetX,  offsetY);

        final boolean isRtl = isLayoutRtl();

        final int startIndex = isRtl ? childCount - 1 : 0;
        final int endIndex = isRtl ? -1 : childCount;
        final int delta = isRtl ? -1 : 1;

        int verticalPadding = getPaddingTop() + getPaddingBottom();
        int childLeft = offsetX + getRelativeChildOffset(startIndex);
        for (int i = startIndex; i != endIndex; i += delta) {
            final View child = getPageAt(i);
            LayoutParams lp = (LayoutParams) child.getLayoutParams();
            int childTop;

            if (lp.isFullScreenPage) {
                childTop = offsetY;
            } else {
                childTop = offsetY + getPaddingTop();
                if (mCenterPagesVertically) {
                    childTop += ((getViewportHeight() - verticalPadding) - child.getMeasuredHeight()) / 2;
                }
            }

            if (child.getVisibility() != View.GONE) {
                final int childWidth = child.getMeasuredWidth();
                final int childHeight = child.getMeasuredHeight();

                if (DEBUG) Log.d(TAG, "\tlayout-child" + i + ": " + childLeft + ", " + childTop);
                child.layout(childLeft, childTop,
                        childLeft + child.getMeasuredWidth(), childTop + childHeight);
                childLeft += childWidth + mPageSpacing;
            }
        }

        if (mFirstLayout && mCurrentPage >= 0 && mCurrentPage < getChildCount()) {
            setHorizontalScrollBarEnabled(false);
            updateCurrentPageScroll();
            setHorizontalScrollBarEnabled(true);
            mFirstLayout = false;
        }

        if (childCount > 0) {
            final int index = isLayoutRtl() ? 0 : childCount - 1;
            mMaxScrollX = getChildOffset(index) - getRelativeChildOffset(index);
        } else {
            mMaxScrollX = 0;
        }

        if (mScroller.isFinished() && mChildCountOnLastLayout != getChildCount() &&
                !mDeferringForDelete) {
            setCurrentPage(getNextPage());
        }
        mChildCountOnLastLayout = getChildCount();
    }

    protected void screenScrolled(int screenCenter) {
        boolean isInOverscroll = mOverScrollX < 0 || mOverScrollX > mMaxScrollX;

        if (mFadeInAdjacentScreens && !isInOverscroll) {
            for (int i = 0; i < getChildCount(); i++) {
                View child = getChildAt(i);
                if (child != null) {
                    float scrollProgress = getScrollProgress(screenCenter, child, i);
                    float alpha = 1 - Math.abs(scrollProgress);
                    child.setAlpha(alpha);
                }
            }
            invalidate();
        }
    }

    @Override
    public void onChildViewAdded(View parent, View child) {
        // Update the page indicator, we don't update the page indicator as we
        // add/remove pages
        if (mPageIndicator != null && !isReordering(false)) {
            mPageIndicator.addMarker(indexOfChild(child));
        }

        // This ensures that when children are added, they get the correct transforms / alphas
        // in accordance with any scroll effects.
        mForceScreenScrolled = true;
        mRecomputePageSpacing = true;

        invalidate();
        invalidateCachedOffsets();
    }

    @Override
    public void onChildViewRemoved(View parent, View child) {
        mForceScreenScrolled = true;
        invalidate();
        invalidateCachedOffsets();
    }

    private void removeMarkerForView(int index) {
        // Update the page indicator, we don't update the page indicator as we
        // add/remove pages
        if (mPageIndicator != null && !isReordering(false)) {
            mPageIndicator.removeMarker(index);
        }
    }

    @Override
    public void removeView(View v) {
        // XXX: We should find a better way to hook into this before the view
        // gets removed form its parent...
        removeMarkerForView(indexOfChild(v));
        super.removeView(v);
    }
    @Override
    public void removeViewInLayout(View v) {
        // XXX: We should find a better way to hook into this before the view
        // gets removed form its parent...
        removeMarkerForView(indexOfChild(v));
        super.removeViewInLayout(v);
    }
    @Override
    public void removeViewAt(int index) {
        // XXX: We should find a better way to hook into this before the view
        // gets removed form its parent...
        removeViewAt(index);
        super.removeViewAt(index);
    }
    @Override
    public void removeAllViewsInLayout() {
        // Update the page indicator, we don't update the page indicator as we
        // add/remove pages
        if (mPageIndicator != null) {
            mPageIndicator.removeAllMarkers();
        }

        super.removeAllViewsInLayout();
    }

    protected void invalidateCachedOffsets() {
        int count = getChildCount();
        if (count == 0) {
            mChildRelativeOffsets = null;
            return;
        }

        mChildRelativeOffsets = new int[count];
        for (int i = 0; i < count; i++) {
            mChildRelativeOffsets[i] = -1;
        }
    }

    protected int getChildOffset(int index) {
        if (index < 0 || index > getChildCount() - 1) return 0;

        final boolean isRtl = isLayoutRtl();

        if (isRtl) index = getChildCount() - index - 1;
        int offset = getPageAt(index).getLeft() - getViewportOffsetX();

        return offset;
    }

    protected int getRelativeChildOffset(int index) {
        if (index < 0 || index > getChildCount() - 1) return 0;

        if (mChildRelativeOffsets != null && mChildRelativeOffsets[index] != -1) {
            return mChildRelativeOffsets[index];
        } else {
            final int padding = getPaddingLeft() + getPaddingRight();
            final int offset = getPaddingLeft() +
                    (getViewportWidth() - padding - getChildWidth(index)) / 2;
            if (mChildRelativeOffsets != null) {
                mChildRelativeOffsets[index] = offset;
            }
            return offset;
        }
    }

    void boundByReorderablePages(boolean isReordering, int[] range) {
        // Do nothing
    }

    // TODO: Fix this
    protected void getVisiblePages(int[] range) {
        range[0] = 0;
        range[1] = getPageCount() - 1;

        /*
        final int pageCount = getChildCount();

        if (pageCount > 0) {
            final int screenWidth = getViewportWidth();
            int leftScreen = 0;
            int rightScreen = 0;
            int offsetX = getViewportOffsetX() + getScrollX();
            View currPage = getPageAt(leftScreen);
            while (leftScreen < pageCount - 1 &&
                    currPage.getX() + currPage.getWidth() -
                    currPage.getPaddingRight() < offsetX) {
                leftScreen++;
                currPage = getPageAt(leftScreen);
            }
            rightScreen = leftScreen;
            currPage = getPageAt(rightScreen + 1);
            while (rightScreen < pageCount - 1 &&
                    currPage.getX() - currPage.getPaddingLeft() < offsetX + screenWidth) {
                rightScreen++;
                currPage = getPageAt(rightScreen + 1);
            }

            // TEMP: this is a hacky way to ensure that animations to new pages are not clipped
            // because we don't draw them while scrolling?
            range[0] = Math.max(0, leftScreen - 1);
            range[1] = Math.min(rightScreen + 1, getChildCount() - 1);
        } else {
            range[0] = -1;
            range[1] = -1;
        }
        */
    }

    protected boolean shouldDrawChild(View child) {
        return child.getAlpha() > 0;
    }

    @Override
    protected void dispatchDraw(Canvas canvas) {
        int halfScreenSize = getViewportWidth() / 2;
        // mOverScrollX is equal to getScrollX() when we're within the normal scroll range.
        // Otherwise it is equal to the scaled overscroll position.
        int screenCenter = mOverScrollX + halfScreenSize;

        if (screenCenter != mLastScreenCenter || mForceScreenScrolled) {
            // set mForceScreenScrolled before calling screenScrolled so that screenScrolled can
            // set it for the next frame
            mForceScreenScrolled = false;
            screenScrolled(screenCenter);
            mLastScreenCenter = screenCenter;
        }

        // Find out which screens are visible; as an optimization we only call draw on them
        final int pageCount = getChildCount();
        if (pageCount > 0) {
            getVisiblePages(mTempVisiblePagesRange);
            final int leftScreen = mTempVisiblePagesRange[0];
            final int rightScreen = mTempVisiblePagesRange[1];
            if (leftScreen != -1 && rightScreen != -1) {
                final long drawingTime = getDrawingTime();
                // Clip to the bounds
                canvas.save();
                canvas.clipRect(getScrollX(), getScrollY(), getScrollX() + getRight() - getLeft(),
                        getScrollY() + getBottom() - getTop());

                // Draw all the children, leaving the drag view for last
                for (int i = pageCount - 1; i >= 0; i--) {
                    final View v = getPageAt(i);
                    if (v == mDragView) continue;
                    if (mForceDrawAllChildrenNextFrame ||
                               (leftScreen <= i && i <= rightScreen && shouldDrawChild(v))) {
                        drawChild(canvas, v, drawingTime);
                    }
                }
                // Draw the drag view on top (if there is one)
                if (mDragView != null) {
                    drawChild(canvas, mDragView, drawingTime);
                }

                mForceDrawAllChildrenNextFrame = false;
                canvas.restore();
            }
        }
    }

    @Override
    public boolean requestChildRectangleOnScreen(View child, Rect rectangle, boolean immediate) {
        int page = indexToPage(indexOfChild(child));
        if (page != mCurrentPage || !mScroller.isFinished()) {
            snapToPage(page);
            return true;
        }
        return false;
    }

    @Override
    protected boolean onRequestFocusInDescendants(int direction, Rect previouslyFocusedRect) {
        int focusablePage;
        if (mNextPage != INVALID_PAGE) {
            focusablePage = mNextPage;
        } else {
            focusablePage = mCurrentPage;
        }
        View v = getPageAt(focusablePage);
        if (v != null) {
            return v.requestFocus(direction, previouslyFocusedRect);
        }
        return false;
    }

    @Override
    public boolean dispatchUnhandledMove(View focused, int direction) {
        // XXX-RTL: This will be fixed in a future CL
        if (direction == View.FOCUS_LEFT) {
            if (getCurrentPage() > 0) {
                snapToPage(getCurrentPage() - 1);
                return true;
            }
        } else if (direction == View.FOCUS_RIGHT) {
            if (getCurrentPage() < getPageCount() - 1) {
                snapToPage(getCurrentPage() + 1);
                return true;
            }
        }
        return super.dispatchUnhandledMove(focused, direction);
    }

    @Override
    public void addFocusables(ArrayList<View> views, int direction, int focusableMode) {
        // XXX-RTL: This will be fixed in a future CL
        if (mCurrentPage >= 0 && mCurrentPage < getPageCount()) {
            getPageAt(mCurrentPage).addFocusables(views, direction, focusableMode);
        }
        if (direction == View.FOCUS_LEFT) {
            if (mCurrentPage > 0) {
                getPageAt(mCurrentPage - 1).addFocusables(views, direction, focusableMode);
            }
        } else if (direction == View.FOCUS_RIGHT){
            if (mCurrentPage < getPageCount() - 1) {
                getPageAt(mCurrentPage + 1).addFocusables(views, direction, focusableMode);
            }
        }
    }

    /**
     * If one of our descendant views decides that it could be focused now, only
     * pass that along if it's on the current page.
     *
     * This happens when live folders requery, and if they're off page, they
     * end up calling requestFocus, which pulls it on page.
     */
    @Override
    public void focusableViewAvailable(View focused) {
        View current = getPageAt(mCurrentPage);
        View v = focused;
        while (true) {
            if (v == current) {
                super.focusableViewAvailable(focused);
                return;
            }
            if (v == this) {
                return;
            }
            ViewParent parent = v.getParent();
            if (parent instanceof View) {
                v = (View)v.getParent();
            } else {
                return;
            }
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void requestDisallowInterceptTouchEvent(boolean disallowIntercept) {
        if (disallowIntercept) {
            // We need to make sure to cancel our long press if
            // a scrollable widget takes over touch events
            final View currentPage = getPageAt(mCurrentPage);
            currentPage.cancelLongPress();
        }
        super.requestDisallowInterceptTouchEvent(disallowIntercept);
    }

    /**
     * Return true if a tap at (x, y) should trigger a flip to the previous page.
     */
    protected boolean hitsPreviousPage(float x, float y) {
        if (isLayoutRtl()) {
            return (x > (getViewportOffsetX() + getViewportWidth() -
                    getRelativeChildOffset(mCurrentPage) + mPageSpacing));
        }
        return (x < getViewportOffsetX() + getRelativeChildOffset(mCurrentPage) - mPageSpacing);
    }

    /**
     * Return true if a tap at (x, y) should trigger a flip to the next page.
     */
    protected boolean hitsNextPage(float x, float y) {
        if (isLayoutRtl()) {
            return (x < getViewportOffsetX() + getRelativeChildOffset(mCurrentPage) - mPageSpacing);
        }
        return  (x > (getViewportOffsetX() + getViewportWidth() -
                getRelativeChildOffset(mCurrentPage) + mPageSpacing));
    }

    /** Returns whether x and y originated within the buffered viewport */
    private boolean isTouchPointInViewportWithBuffer(int x, int y) {
        mTmpRect.set(mViewport.left - mViewport.width() / 2, mViewport.top,
                mViewport.right + mViewport.width() / 2, mViewport.bottom);
        return mTmpRect.contains(x, y);
    }

    /** Returns whether x and y originated within the current page view bounds */
    private boolean isTouchPointInCurrentPage(int x, int y) {
        View v = getPageAt(getCurrentPage());
        if (v != null) {
            mTmpRect.set((v.getLeft() - getScrollX()), 0, (v.getRight() - getScrollX()),
                    v.getBottom());
            return mTmpRect.contains(x, y);
        }
        return false;
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        if (DISABLE_TOUCH_INTERACTION) {
            return false;
        }

        /*
         * This method JUST determines whether we want to intercept the motion.
         * If we return true, onTouchEvent will be called and we do the actual
         * scrolling there.
         */
        acquireVelocityTrackerAndAddMovement(ev);

        // Skip touch handling if there are no pages to swipe
        if (getChildCount() <= 0) return super.onInterceptTouchEvent(ev);

        /*
         * Shortcut the most recurring case: the user is in the dragging
         * state and he is moving his finger.  We want to intercept this
         * motion.
         */
        final int action = ev.getAction();
        if ((action == MotionEvent.ACTION_MOVE) &&
                (mTouchState == TOUCH_STATE_SCROLLING)) {
            return true;
        }

        switch (action & MotionEvent.ACTION_MASK) {
            case MotionEvent.ACTION_MOVE: {
                /*
                 * mIsBeingDragged == false, otherwise the shortcut would have caught it. Check
                 * whether the user has moved far enough from his original down touch.
                 */
                if (mActivePointerId != INVALID_POINTER) {
                    determineScrollingStart(ev);
                    break;
                }
                // if mActivePointerId is INVALID_POINTER, then we must have missed an ACTION_DOWN
                // event. in that case, treat the first occurence of a move event as a ACTION_DOWN
                // i.e. fall through to the next case (don't break)
                // (We sometimes miss ACTION_DOWN events in Workspace because it ignores all events
                // while it's small- this was causing a crash before we checked for INVALID_POINTER)
            }

            case MotionEvent.ACTION_DOWN: {
                final float x = ev.getX();
                final float y = ev.getY();
                // Remember location of down touch
                mDownMotionX = x;
                mDownMotionY = y;
                mDownScrollX = getScrollX();
                mLastMotionX = x;
                mLastMotionY = y;
                float[] p = mapPointFromViewToParent(this, x, y);
                mParentDownMotionX = p[0];
                mParentDownMotionY = p[1];
                mLastMotionXRemainder = 0;
                mTotalMotionX = 0;
                mActivePointerId = ev.getPointerId(0);

                // Determine if the down event is within the threshold to be an edge swipe
                int leftEdgeBoundary = getViewportOffsetX() + mEdgeSwipeRegionSize;
                int rightEdgeBoundary = getMeasuredWidth() - getViewportOffsetX() - mEdgeSwipeRegionSize;
                if ((mDownMotionX <= leftEdgeBoundary || mDownMotionX >= rightEdgeBoundary)) {
                    mDownEventOnEdge = true;
                }

                /*
                 * If being flinged and user touches the screen, initiate drag;
                 * otherwise don't.  mScroller.isFinished should be false when
                 * being flinged.
                 */
                final int xDist = Math.abs(mScroller.getFinalX() - mScroller.getCurrX());
                final boolean finishedScrolling = (mScroller.isFinished() || xDist < mTouchSlop);
                if (finishedScrolling) {
                    mTouchState = TOUCH_STATE_REST;
                    mScroller.abortAnimation();
                } else {
                    if (isTouchPointInViewportWithBuffer((int) mDownMotionX, (int) mDownMotionY)) {
                        mTouchState = TOUCH_STATE_SCROLLING;
                    } else {
                        mTouchState = TOUCH_STATE_REST;
                    }
                }

                // check if this can be the beginning of a tap on the side of the pages
                // to scroll the current page
                if (!DISABLE_TOUCH_SIDE_PAGES) {
                    if (mTouchState != TOUCH_STATE_PREV_PAGE && mTouchState != TOUCH_STATE_NEXT_PAGE) {
                        if (getChildCount() > 0) {
                            if (hitsPreviousPage(x, y)) {
                                mTouchState = TOUCH_STATE_PREV_PAGE;
                            } else if (hitsNextPage(x, y)) {
                                mTouchState = TOUCH_STATE_NEXT_PAGE;
                            }
                        }
                    }
                }
                break;
            }

            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
                resetTouchState();
                // Just intercept the touch event on up if we tap outside the strict viewport
                if (!isTouchPointInCurrentPage((int) mLastMotionX, (int) mLastMotionY)) {
                    return true;
                }
                break;

            case MotionEvent.ACTION_POINTER_UP:
                onSecondaryPointerUp(ev);
                releaseVelocityTracker();
                break;
        }

        /*
         * The only time we want to intercept motion events is if we are in the
         * drag mode.
         */
        return mTouchState != TOUCH_STATE_REST;
    }

    protected void determineScrollingStart(MotionEvent ev) {
        determineScrollingStart(ev, 1.0f);
    }

    /*
     * Determines if we should change the touch state to start scrolling after the
     * user moves their touch point too far.
     */
    protected void determineScrollingStart(MotionEvent ev, float touchSlopScale) {
        // Disallow scrolling if we don't have a valid pointer index
        final int pointerIndex = ev.findPointerIndex(mActivePointerId);
        if (pointerIndex == -1) return;

        // Disallow scrolling if we started the gesture from outside the viewport
        final float x = ev.getX(pointerIndex);
        final float y = ev.getY(pointerIndex);
        if (!isTouchPointInViewportWithBuffer((int) x, (int) y)) return;

        // If we're only allowing edge swipes, we break out early if the down event wasn't
        // at the edge.
        if (mOnlyAllowEdgeSwipes && !mDownEventOnEdge) return;

        final int xDiff = (int) Math.abs(x - mLastMotionX);
        final int yDiff = (int) Math.abs(y - mLastMotionY);

        final int touchSlop = Math.round(touchSlopScale * mTouchSlop);
        boolean xPaged = xDiff > mPagingTouchSlop;
        boolean xMoved = xDiff > touchSlop;
        boolean yMoved = yDiff > touchSlop;

        if (xMoved || xPaged || yMoved) {
            if (mUsePagingTouchSlop ? xPaged : xMoved) {
                // Scroll if the user moved far enough along the X axis
                mTouchState = TOUCH_STATE_SCROLLING;
                mTotalMotionX += Math.abs(mLastMotionX - x);
                mLastMotionX = x;
                mLastMotionXRemainder = 0;
                mTouchX = getViewportOffsetX() + getScrollX();
                mSmoothingTime = System.nanoTime() / NANOTIME_DIV;
                pageBeginMoving();
            }
        }
    }

    protected float getMaxScrollProgress() {
        return 1.0f;
    }

    protected void cancelCurrentPageLongPress() {
        if (mAllowLongPress) {
            //mAllowLongPress = false;
            // Try canceling the long press. It could also have been scheduled
            // by a distant descendant, so use the mAllowLongPress flag to block
            // everything
            final View currentPage = getPageAt(mCurrentPage);
            if (currentPage != null) {
                currentPage.cancelLongPress();
            }
        }
    }

    protected float getBoundedScrollProgress(int screenCenter, View v, int page) {
        final int halfScreenSize = getViewportWidth() / 2;

        screenCenter = Math.min(getScrollX() + halfScreenSize, screenCenter);
        screenCenter = Math.max(halfScreenSize,  screenCenter);

        return getScrollProgress(screenCenter, v, page);
    }

    protected float getScrollProgress(int screenCenter, View v, int page) {
        final int halfScreenSize = getViewportWidth() / 2;

        int totalDistance = v.getMeasuredWidth() + mPageSpacing;
        int delta = screenCenter - (getChildOffset(page) -
                getRelativeChildOffset(page) + halfScreenSize);

        float scrollProgress = delta / (totalDistance * 1.0f);
        scrollProgress = Math.min(scrollProgress, getMaxScrollProgress());
        scrollProgress = Math.max(scrollProgress, - getMaxScrollProgress());
        return scrollProgress;
    }

    // This curve determines how the effect of scrolling over the limits of the page dimishes
    // as the user pulls further and further from the bounds
    private float overScrollInfluenceCurve(float f) {
        f -= 1.0f;
        return f * f * f + 1.0f;
    }

    protected void acceleratedOverScroll(float amount) {
        int screenSize = getViewportWidth();

        // We want to reach the max over scroll effect when the user has
        // over scrolled half the size of the screen
        float f = OVERSCROLL_ACCELERATE_FACTOR * (amount / screenSize);

        if (f == 0) return;

        // Clamp this factor, f, to -1 < f < 1
        if (Math.abs(f) >= 1) {
            f /= Math.abs(f);
        }

        int overScrollAmount = (int) Math.round(f * screenSize);
        if (amount < 0) {
            mOverScrollX = overScrollAmount;
            super.scrollTo(0, getScrollY());
        } else {
            mOverScrollX = mMaxScrollX + overScrollAmount;
            super.scrollTo(mMaxScrollX, getScrollY());
        }
        invalidate();
    }

    protected void dampedOverScroll(float amount) {
        int screenSize = getViewportWidth();

        float f = (amount / screenSize);

        if (f == 0) return;
        f = f / (Math.abs(f)) * (overScrollInfluenceCurve(Math.abs(f)));

        // Clamp this factor, f, to -1 < f < 1
        if (Math.abs(f) >= 1) {
            f /= Math.abs(f);
        }

        int overScrollAmount = (int) Math.round(OVERSCROLL_DAMP_FACTOR * f * screenSize);
        if (amount < 0) {
            mOverScrollX = overScrollAmount;
            super.scrollTo(0, getScrollY());
        } else {
            mOverScrollX = mMaxScrollX + overScrollAmount;
            super.scrollTo(mMaxScrollX, getScrollY());
        }
        invalidate();
    }

    protected void overScroll(float amount) {
        dampedOverScroll(amount);
    }

    protected float maxOverScroll() {
        // Using the formula in overScroll, assuming that f = 1.0 (which it should generally not
        // exceed). Used to find out how much extra wallpaper we need for the over scroll effect
        float f = 1.0f;
        f = f / (Math.abs(f)) * (overScrollInfluenceCurve(Math.abs(f)));
        return OVERSCROLL_DAMP_FACTOR * f;
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        if (DISABLE_TOUCH_INTERACTION) {
            return false;
        }

        // Skip touch handling if there are no pages to swipe
        if (getChildCount() <= 0) return super.onTouchEvent(ev);

        acquireVelocityTrackerAndAddMovement(ev);

        final int action = ev.getAction();

        switch (action & MotionEvent.ACTION_MASK) {
        case MotionEvent.ACTION_DOWN:
            /*
             * If being flinged and user touches, stop the fling. isFinished
             * will be false if being flinged.
             */
            if (!mScroller.isFinished()) {
                mScroller.abortAnimation();
            }

            // Remember where the motion event started
            mDownMotionX = mLastMotionX = ev.getX();
            mDownMotionY = mLastMotionY = ev.getY();
            mDownScrollX = getScrollX();
            float[] p = mapPointFromViewToParent(this, mLastMotionX, mLastMotionY);
            mParentDownMotionX = p[0];
            mParentDownMotionY = p[1];
            mLastMotionXRemainder = 0;
            mTotalMotionX = 0;
            mActivePointerId = ev.getPointerId(0);

            // Determine if the down event is within the threshold to be an edge swipe
            int leftEdgeBoundary = getViewportOffsetX() + mEdgeSwipeRegionSize;
            int rightEdgeBoundary = getMeasuredWidth() - getViewportOffsetX() - mEdgeSwipeRegionSize;
            if ((mDownMotionX <= leftEdgeBoundary || mDownMotionX >= rightEdgeBoundary)) {
                mDownEventOnEdge = true;
            }

            if (mTouchState == TOUCH_STATE_SCROLLING) {
                pageBeginMoving();
            }
            break;

        case MotionEvent.ACTION_MOVE:
            if (mTouchState == TOUCH_STATE_SCROLLING) {
                // Scroll to follow the motion event
                final int pointerIndex = ev.findPointerIndex(mActivePointerId);

                if (pointerIndex == -1) return true;

                final float x = ev.getX(pointerIndex);
                final float deltaX = mLastMotionX + mLastMotionXRemainder - x;

                mTotalMotionX += Math.abs(deltaX);

                // Only scroll and update mLastMotionX if we have moved some discrete amount.  We
                // keep the remainder because we are actually testing if we've moved from the last
                // scrolled position (which is discrete).
                if (Math.abs(deltaX) >= 1.0f) {
                    mTouchX += deltaX;
                    mSmoothingTime = System.nanoTime() / NANOTIME_DIV;
                    if (!mDeferScrollUpdate) {
                        scrollBy((int) deltaX, 0);
                        if (DEBUG) Log.d(TAG, "onTouchEvent().Scrolling: " + deltaX);
                    } else {
                        invalidate();
                    }
                    mLastMotionX = x;
                    mLastMotionXRemainder = deltaX - (int) deltaX;
                } else {
                    awakenScrollBars();
                }
            } else if (mTouchState == TOUCH_STATE_REORDERING) {
                // Update the last motion position
                mLastMotionX = ev.getX();
                mLastMotionY = ev.getY();

                // Update the parent down so that our zoom animations take this new movement into
                // account
                float[] pt = mapPointFromViewToParent(this, mLastMotionX, mLastMotionY);
                mParentDownMotionX = pt[0];
                mParentDownMotionY = pt[1];
                updateDragViewTranslationDuringDrag();

                // Find the closest page to the touch point
                final int dragViewIndex = indexOfChild(mDragView);
                int bufferSize = (int) (REORDERING_SIDE_PAGE_BUFFER_PERCENTAGE *
                    getViewportWidth());
                int leftBufferEdge = (int) (mapPointFromViewToParent(this, mViewport.left, 0)[0]
                        + bufferSize);
                int rightBufferEdge = (int) (mapPointFromViewToParent(this, mViewport.right, 0)[0]
                        - bufferSize);

                // Change the drag view if we are hovering over the drop target
                boolean isHoveringOverDelete = isHoveringOverDeleteDropTarget(
                        (int) mParentDownMotionX, (int) mParentDownMotionY);
                setPageHoveringOverDeleteDropTarget(dragViewIndex, isHoveringOverDelete);

                if (DEBUG) Log.d(TAG, "leftBufferEdge: " + leftBufferEdge);
                if (DEBUG) Log.d(TAG, "rightBufferEdge: " + rightBufferEdge);
                if (DEBUG) Log.d(TAG, "mLastMotionX: " + mLastMotionX);
                if (DEBUG) Log.d(TAG, "mLastMotionY: " + mLastMotionY);
                if (DEBUG) Log.d(TAG, "mParentDownMotionX: " + mParentDownMotionX);
                if (DEBUG) Log.d(TAG, "mParentDownMotionY: " + mParentDownMotionY);

                float parentX = mParentDownMotionX;
                int pageIndexToSnapTo = -1;
                if (parentX < leftBufferEdge && dragViewIndex > 0) {
                    pageIndexToSnapTo = dragViewIndex - 1;
                } else if (parentX > rightBufferEdge && dragViewIndex < getChildCount() - 1) {
                    pageIndexToSnapTo = dragViewIndex + 1;
                }

                final int pageUnderPointIndex = pageIndexToSnapTo;
                if (pageUnderPointIndex > -1 && !isHoveringOverDelete) {
                    mTempVisiblePagesRange[0] = 0;
                    mTempVisiblePagesRange[1] = getPageCount() - 1;
                    boundByReorderablePages(true, mTempVisiblePagesRange);
                    if (mTempVisiblePagesRange[0] <= pageUnderPointIndex &&
                            pageUnderPointIndex <= mTempVisiblePagesRange[1] &&
                            pageUnderPointIndex != mSidePageHoverIndex && mScroller.isFinished()) {
                        mSidePageHoverIndex = pageUnderPointIndex;
                        mSidePageHoverRunnable = new Runnable() {
                            @Override
                            public void run() {
                                // Update the down scroll position to account for the fact that the
                                // current page is moved
                                mDownScrollX = getChildOffset(pageUnderPointIndex)
                                        - getRelativeChildOffset(pageUnderPointIndex);

                                // Setup the scroll to the correct page before we swap the views
                                snapToPage(pageUnderPointIndex);

                                // For each of the pages between the paged view and the drag view,
                                // animate them from the previous position to the new position in
                                // the layout (as a result of the drag view moving in the layout)
                                int shiftDelta = (dragViewIndex < pageUnderPointIndex) ? -1 : 1;
                                int lowerIndex = (dragViewIndex < pageUnderPointIndex) ?
                                        dragViewIndex + 1 : pageUnderPointIndex;
                                int upperIndex = (dragViewIndex > pageUnderPointIndex) ?
                                        dragViewIndex - 1 : pageUnderPointIndex;
                                for (int i = lowerIndex; i <= upperIndex; ++i) {
                                    View v = getChildAt(i);
                                    // dragViewIndex < pageUnderPointIndex, so after we remove the
                                    // drag view all subsequent views to pageUnderPointIndex will
                                    // shift down.
                                    int oldX = getViewportOffsetX() + getChildOffset(i);
                                    int newX = getViewportOffsetX() + getChildOffset(i + shiftDelta);

                                    // Animate the view translation from its old position to its new
                                    // position
                                    AnimatorSet anim = (AnimatorSet) v.getTag(ANIM_TAG_KEY);
                                    if (anim != null) {
                                        anim.cancel();
                                    }

                                    v.setTranslationX(oldX - newX);
                                    anim = new AnimatorSet();
                                    anim.setDuration(REORDERING_REORDER_REPOSITION_DURATION);
                                    anim.playTogether(
                                            ObjectAnimator.ofFloat(v, "translationX", 0f));
                                    anim.start();
                                    v.setTag(anim);
                                }

                                removeView(mDragView);
                                onRemoveView(mDragView, false);
                                addView(mDragView, pageUnderPointIndex);
                                onAddView(mDragView, pageUnderPointIndex);
                                mSidePageHoverIndex = -1;
                                mPageIndicator.setActiveMarker(getNextPage());
                            }
                        };
                        postDelayed(mSidePageHoverRunnable, REORDERING_SIDE_PAGE_HOVER_TIMEOUT);
                    }
                } else {
                    removeCallbacks(mSidePageHoverRunnable);
                    mSidePageHoverIndex = -1;
                }
            } else {
                determineScrollingStart(ev);
            }
            break;

        case MotionEvent.ACTION_UP:
            if (mTouchState == TOUCH_STATE_SCROLLING) {
                final int activePointerId = mActivePointerId;
                final int pointerIndex = ev.findPointerIndex(activePointerId);
                final float x = ev.getX(pointerIndex);
                final VelocityTracker velocityTracker = mVelocityTracker;
                velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
                int velocityX = (int) velocityTracker.getXVelocity(activePointerId);
                final int deltaX = (int) (x - mDownMotionX);
                final int pageWidth = getPageAt(mCurrentPage).getMeasuredWidth();
                boolean isSignificantMove = Math.abs(deltaX) > pageWidth *
                        SIGNIFICANT_MOVE_THRESHOLD;

                mTotalMotionX += Math.abs(mLastMotionX + mLastMotionXRemainder - x);

                boolean isFling = mTotalMotionX > MIN_LENGTH_FOR_FLING &&
                        Math.abs(velocityX) > mFlingThresholdVelocity;

                // In the case that the page is moved far to one direction and then is flung
                // in the opposite direction, we use a threshold to determine whether we should
                // just return to the starting page, or if we should skip one further.
                boolean returnToOriginalPage = false;
                if (Math.abs(deltaX) > pageWidth * RETURN_TO_ORIGINAL_PAGE_THRESHOLD &&
                        Math.signum(velocityX) != Math.signum(deltaX) && isFling) {
                    returnToOriginalPage = true;
                }

                int finalPage;
                // We give flings precedence over large moves, which is why we short-circuit our
                // test for a large move if a fling has been registered. That is, a large
                // move to the left and fling to the right will register as a fling to the right.
                final boolean isRtl = isLayoutRtl();
                boolean isDeltaXLeft = isRtl ? deltaX > 0 : deltaX < 0;
                boolean isVelocityXLeft = isRtl ? velocityX > 0 : velocityX < 0;
                if (((isSignificantMove && !isDeltaXLeft && !isFling) ||
                        (isFling && !isVelocityXLeft)) && mCurrentPage > 0) {
                    finalPage = returnToOriginalPage ? mCurrentPage : mCurrentPage - 1;
                    snapToPageWithVelocity(finalPage, velocityX);
                } else if (((isSignificantMove && isDeltaXLeft && !isFling) ||
                        (isFling && isVelocityXLeft)) &&
                        mCurrentPage < getChildCount() - 1) {
                    finalPage = returnToOriginalPage ? mCurrentPage : mCurrentPage + 1;
                    snapToPageWithVelocity(finalPage, velocityX);
                } else {
                    snapToDestination();
                }            } else if (mTouchState == TOUCH_STATE_PREV_PAGE) {
                // at this point we have not moved beyond the touch slop
                // (otherwise mTouchState would be TOUCH_STATE_SCROLLING), so
                // we can just page
                int nextPage = Math.max(0, mCurrentPage - 1);
                if (nextPage != mCurrentPage) {
                    snapToPage(nextPage);
                } else {
                    snapToDestination();
                }
            } else if (mTouchState == TOUCH_STATE_NEXT_PAGE) {
                // at this point we have not moved beyond the touch slop
                // (otherwise mTouchState would be TOUCH_STATE_SCROLLING), so
                // we can just page
                int nextPage = Math.min(getChildCount() - 1, mCurrentPage + 1);
                if (nextPage != mCurrentPage) {
                    snapToPage(nextPage);
                } else {
                    snapToDestination();
                }
            } else if (mTouchState == TOUCH_STATE_REORDERING) {
                // Update the last motion position
                mLastMotionX = ev.getX();
                mLastMotionY = ev.getY();

                // Update the parent down so that our zoom animations take this new movement into
                // account
                float[] pt = mapPointFromViewToParent(this, mLastMotionX, mLastMotionY);
                mParentDownMotionX = pt[0];
                mParentDownMotionY = pt[1];
                updateDragViewTranslationDuringDrag();
                boolean handledFling = false;
                if (!DISABLE_FLING_TO_DELETE) {
                    // Check the velocity and see if we are flinging-to-delete
                    PointF flingToDeleteVector = isFlingingToDelete();
                    if (flingToDeleteVector != null) {
                        onFlingToDelete(flingToDeleteVector);
                        handledFling = true;
                    }
                }
                if (!handledFling && isHoveringOverDeleteDropTarget((int) mParentDownMotionX,
                        (int) mParentDownMotionY)) {
                    onDropToDelete();
                }
            } else {
                onUnhandledTap(ev);
            }

            // Remove the callback to wait for the side page hover timeout
            removeCallbacks(mSidePageHoverRunnable);
            // End any intermediate reordering states
            resetTouchState();
            break;

        case MotionEvent.ACTION_CANCEL:
            if (mTouchState == TOUCH_STATE_SCROLLING) {
                snapToDestination();
            }
            resetTouchState();
            break;

        case MotionEvent.ACTION_POINTER_UP:
            onSecondaryPointerUp(ev);
            break;
        }

        return true;
    }

    public void onFlingToDelete(View v) {}
    public void onRemoveView(View v, boolean deletePermanently) {}
    public void onRemoveViewAnimationCompleted() {}
    public void onAddView(View v, int index) {}

    private void resetTouchState() {
        releaseVelocityTracker();
        endReordering();
        mTouchState = TOUCH_STATE_REST;
        mActivePointerId = INVALID_POINTER;
        mDownEventOnEdge = false;
    }

    protected void onUnhandledTap(MotionEvent ev) {}

    @Override
    public boolean onGenericMotionEvent(MotionEvent event) {
        if ((event.getSource() & InputDevice.SOURCE_CLASS_POINTER) != 0) {
            switch (event.getAction()) {
                case MotionEvent.ACTION_SCROLL: {
                    // Handle mouse (or ext. device) by shifting the page depending on the scroll
                    final float vscroll;
                    final float hscroll;
                    if ((event.getMetaState() & KeyEvent.META_SHIFT_ON) != 0) {
                        vscroll = 0;
                        hscroll = event.getAxisValue(MotionEvent.AXIS_VSCROLL);
                    } else {
                        vscroll = -event.getAxisValue(MotionEvent.AXIS_VSCROLL);
                        hscroll = event.getAxisValue(MotionEvent.AXIS_HSCROLL);
                    }
                    if (hscroll != 0 || vscroll != 0) {
                        boolean isForwardScroll = isLayoutRtl() ? (hscroll < 0 || vscroll < 0)
                                                         : (hscroll > 0 || vscroll > 0);
                        if (isForwardScroll) {
                            scrollRight();
                        } else {
                            scrollLeft();
                        }
                        return true;
                    }
                }
            }
        }
        return super.onGenericMotionEvent(event);
    }

    private void acquireVelocityTrackerAndAddMovement(MotionEvent ev) {
        if (mVelocityTracker == null) {
            mVelocityTracker = VelocityTracker.obtain();
        }
        mVelocityTracker.addMovement(ev);
    }

    private void releaseVelocityTracker() {
        if (mVelocityTracker != null) {
            mVelocityTracker.recycle();
            mVelocityTracker = null;
        }
    }

    private void onSecondaryPointerUp(MotionEvent ev) {
        final int pointerIndex = (ev.getAction() & MotionEvent.ACTION_POINTER_INDEX_MASK) >>
                MotionEvent.ACTION_POINTER_INDEX_SHIFT;
        final int pointerId = ev.getPointerId(pointerIndex);
        if (pointerId == mActivePointerId) {
            // This was our active pointer going up. Choose a new
            // active pointer and adjust accordingly.
            // TODO: Make this decision more intelligent.
            final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
            mLastMotionX = mDownMotionX = ev.getX(newPointerIndex);
            mLastMotionY = ev.getY(newPointerIndex);
            mLastMotionXRemainder = 0;
            mActivePointerId = ev.getPointerId(newPointerIndex);
            if (mVelocityTracker != null) {
                mVelocityTracker.clear();
            }
        }
    }

    @Override
    public void requestChildFocus(View child, View focused) {
        super.requestChildFocus(child, focused);
        int page = indexToPage(indexOfChild(child));
        if (page >= 0 && page != getCurrentPage() && !isInTouchMode()) {
            snapToPage(page);
        }
    }

    protected int getChildWidth(int index) {
        return getPageAt(index).getMeasuredWidth();
    }

    int getPageNearestToPoint(float x) {
        int index = 0;
        for (int i = 0; i < getChildCount(); ++i) {
            if (x < getChildAt(i).getRight() - getScrollX()) {
                return index;
            } else {
                index++;
            }
        }
        return Math.min(index, getChildCount() - 1);
    }

    int getPageNearestToCenterOfScreen() {
        int minDistanceFromScreenCenter = Integer.MAX_VALUE;
        int minDistanceFromScreenCenterIndex = -1;
        int screenCenter = getViewportOffsetX() + getScrollX() + (getViewportWidth() / 2);
        final int childCount = getChildCount();
        for (int i = 0; i < childCount; ++i) {
            View layout = (View) getPageAt(i);
            int childWidth = layout.getMeasuredWidth();
            int halfChildWidth = (childWidth / 2);
            int childCenter = getViewportOffsetX() + getChildOffset(i) + halfChildWidth;
            int distanceFromScreenCenter = Math.abs(childCenter - screenCenter);
            if (distanceFromScreenCenter < minDistanceFromScreenCenter) {
                minDistanceFromScreenCenter = distanceFromScreenCenter;
                minDistanceFromScreenCenterIndex = i;
            }
        }
        return minDistanceFromScreenCenterIndex;
    }

    protected void snapToDestination() {
        snapToPage(getPageNearestToCenterOfScreen(), PAGE_SNAP_ANIMATION_DURATION);
    }

    private static class ScrollInterpolator implements Interpolator {
        public ScrollInterpolator() {
        }

        public float getInterpolation(float t) {
            t -= 1.0f;
            return t*t*t*t*t + 1;
        }
    }

    // We want the duration of the page snap animation to be influenced by the distance that
    // the screen has to travel, however, we don't want this duration to be effected in a
    // purely linear fashion. Instead, we use this method to moderate the effect that the distance
    // of travel has on the overall snap duration.
    float distanceInfluenceForSnapDuration(float f) {
        f -= 0.5f; // center the values about 0.
        f *= 0.3f * Math.PI / 2.0f;
        return (float) Math.sin(f);
    }

    protected void snapToPageWithVelocity(int whichPage, int velocity) {
        whichPage = Math.max(0, Math.min(whichPage, getChildCount() - 1));
        int halfScreenSize = getViewportWidth() / 2;

        if (DEBUG) Log.d(TAG, "snapToPage.getChildOffset(): " + getChildOffset(whichPage));
        if (DEBUG) Log.d(TAG, "snapToPageWithVelocity.getRelativeChildOffset(): "
                + getViewportWidth() + ", " + getChildWidth(whichPage));
        final int newX = getChildOffset(whichPage) - getRelativeChildOffset(whichPage);
        int delta = newX - mUnboundedScrollX;
        int duration = 0;

        if (Math.abs(velocity) < mMinFlingVelocity) {
            // If the velocity is low enough, then treat this more as an automatic page advance
            // as opposed to an apparent physical response to flinging
            snapToPage(whichPage, PAGE_SNAP_ANIMATION_DURATION);
            return;
        }

        // Here we compute a "distance" that will be used in the computation of the overall
        // snap duration. This is a function of the actual distance that needs to be traveled;
        // we keep this value close to half screen size in order to reduce the variance in snap
        // duration as a function of the distance the page needs to travel.
        float distanceRatio = Math.min(1f, 1.0f * Math.abs(delta) / (2 * halfScreenSize));
        float distance = halfScreenSize + halfScreenSize *
                distanceInfluenceForSnapDuration(distanceRatio);

        velocity = Math.abs(velocity);
        velocity = Math.max(mMinSnapVelocity, velocity);

        // we want the page's snap velocity to approximately match the velocity at which the
        // user flings, so we scale the duration by a value near to the derivative of the scroll
        // interpolator at zero, ie. 5. We use 4 to make it a little slower.
        duration = 4 * Math.round(1000 * Math.abs(distance / velocity));

        snapToPage(whichPage, delta, duration);
    }

    protected void snapToPage(int whichPage) {
        snapToPage(whichPage, PAGE_SNAP_ANIMATION_DURATION);
    }

    protected void snapToPageImmediately(int whichPage) {
        snapToPage(whichPage, PAGE_SNAP_ANIMATION_DURATION, true);
    }

    protected void snapToPage(int whichPage, int duration) {
        snapToPage(whichPage, duration, false);
    }

    protected void snapToPage(int whichPage, int duration, boolean immediate) {
        whichPage = Math.max(0, Math.min(whichPage, getPageCount() - 1));

        if (DEBUG) Log.d(TAG, "snapToPage.getChildOffset(): " + getChildOffset(whichPage));
        if (DEBUG) Log.d(TAG, "snapToPage.getRelativeChildOffset(): " + getViewportWidth() + ", "
                + getChildWidth(whichPage));
        int newX = getChildOffset(whichPage) - getRelativeChildOffset(whichPage);
        final int sX = mUnboundedScrollX;
        final int delta = newX - sX;
        snapToPage(whichPage, delta, duration, immediate);
    }

    protected void snapToPage(int whichPage, int delta, int duration) {
        snapToPage(whichPage, delta, duration, false);
    }

    protected void snapToPage(int whichPage, int delta, int duration, boolean immediate) {
        mNextPage = whichPage;
        View focusedChild = getFocusedChild();
        if (focusedChild != null && whichPage != mCurrentPage &&
                focusedChild == getPageAt(mCurrentPage)) {
            focusedChild.clearFocus();
        }

        pageBeginMoving();
        awakenScrollBars(duration);
        if (immediate) {
            duration = 0;
        } else if (duration == 0) {
            duration = Math.abs(delta);
        }

        if (!mScroller.isFinished()) mScroller.abortAnimation();
        mScroller.startScroll(mUnboundedScrollX, 0, delta, 0, duration);

        notifyPageSwitchListener();

        // Trigger a compute() to finish switching pages if necessary
        if (immediate) {
            computeScroll();
        }

        mForceScreenScrolled = true;
        invalidate();
    }

    public void scrollLeft() {
        if (mScroller.isFinished()) {
            if (mCurrentPage > 0) snapToPage(mCurrentPage - 1);
        } else {
            if (mNextPage > 0) snapToPage(mNextPage - 1);
        }
    }

    public void scrollRight() {
        if (mScroller.isFinished()) {
            if (mCurrentPage < getChildCount() -1) snapToPage(mCurrentPage + 1);
        } else {
            if (mNextPage < getChildCount() -1) snapToPage(mNextPage + 1);
        }
    }

    public int getPageForView(View v) {
        int result = -1;
        if (v != null) {
            ViewParent vp = v.getParent();
            int count = getChildCount();
            for (int i = 0; i < count; i++) {
                if (vp == getPageAt(i)) {
                    return i;
                }
            }
        }
        return result;
    }

    /**
     * @return True is long presses are still allowed for the current touch
     */
    public boolean allowLongPress() {
        return mAllowLongPress;
    }

    /**
     * Set true to allow long-press events to be triggered, usually checked by
     * {@link Launcher} to accept or block dpad-initiated long-presses.
     */
    public void setAllowLongPress(boolean allowLongPress) {
        mAllowLongPress = allowLongPress;
    }

    public static class SavedState extends BaseSavedState {
        int currentPage = -1;

        SavedState(Parcelable superState) {
            super(superState);
        }

        private SavedState(Parcel in) {
            super(in);
            currentPage = in.readInt();
        }

        @Override
        public void writeToParcel(Parcel out, int flags) {
            super.writeToParcel(out, flags);
            out.writeInt(currentPage);
        }

        public static final Parcelable.Creator<SavedState> CREATOR =
                new Parcelable.Creator<SavedState>() {
            public SavedState createFromParcel(Parcel in) {
                return new SavedState(in);
            }

            public SavedState[] newArray(int size) {
                return new SavedState[size];
            }
        };
    }

    protected void loadAssociatedPages(int page) {
        loadAssociatedPages(page, false);
    }
    protected void loadAssociatedPages(int page, boolean immediateAndOnly) {
        if (mContentIsRefreshable) {
            final int count = getChildCount();
            if (page < count) {
                int lowerPageBound = getAssociatedLowerPageBound(page);
                int upperPageBound = getAssociatedUpperPageBound(page);
                if (DEBUG) Log.d(TAG, "loadAssociatedPages: " + lowerPageBound + "/"
                        + upperPageBound);
                // First, clear any pages that should no longer be loaded
                for (int i = 0; i < count; ++i) {
                    Page layout = (Page) getPageAt(i);
                    if ((i < lowerPageBound) || (i > upperPageBound)) {
                        if (layout.getPageChildCount() > 0) {
                            layout.removeAllViewsOnPage();
                        }
                        mDirtyPageContent.set(i, true);
                    }
                }
                // Next, load any new pages
                for (int i = 0; i < count; ++i) {
                    if ((i != page) && immediateAndOnly) {
                        continue;
                    }
                    if (lowerPageBound <= i && i <= upperPageBound) {
                        if (mDirtyPageContent.get(i)) {
                            syncPageItems(i, (i == page) && immediateAndOnly);
                            mDirtyPageContent.set(i, false);
                        }
                    }
                }
            }
        }
    }

    protected int getAssociatedLowerPageBound(int page) {
        return Math.max(0, page - 1);
    }
    protected int getAssociatedUpperPageBound(int page) {
        final int count = getChildCount();
        return Math.min(page + 1, count - 1);
    }

    /**
     * This method is called ONLY to synchronize the number of pages that the paged view has.
     * To actually fill the pages with information, implement syncPageItems() below.  It is
     * guaranteed that syncPageItems() will be called for a particular page before it is shown,
     * and therefore, individual page items do not need to be updated in this method.
     */
    public abstract void syncPages();

    /**
     * This method is called to synchronize the items that are on a particular page.  If views on
     * the page can be reused, then they should be updated within this method.
     */
    public abstract void syncPageItems(int page, boolean immediate);

    protected void invalidatePageData() {
        invalidatePageData(-1, false);
    }
    protected void invalidatePageData(int currentPage) {
        invalidatePageData(currentPage, false);
    }
    protected void invalidatePageData(int currentPage, boolean immediateAndOnly) {
        if (!mIsDataReady) {
            return;
        }

        if (mContentIsRefreshable) {
            // Force all scrolling-related behavior to end
            mScroller.forceFinished(true);
            mNextPage = INVALID_PAGE;

            // Update all the pages
            syncPages();

            // We must force a measure after we've loaded the pages to update the content width and
            // to determine the full scroll width
            measure(MeasureSpec.makeMeasureSpec(getMeasuredWidth(), MeasureSpec.EXACTLY),
                    MeasureSpec.makeMeasureSpec(getMeasuredHeight(), MeasureSpec.EXACTLY));

            // Set a new page as the current page if necessary
            if (currentPage > -1) {
                setCurrentPage(Math.min(getPageCount() - 1, currentPage));
            }

            // Mark each of the pages as dirty
            final int count = getChildCount();
            mDirtyPageContent.clear();
            for (int i = 0; i < count; ++i) {
                mDirtyPageContent.add(true);
            }

            // Load any pages that are necessary for the current window of views
            loadAssociatedPages(mCurrentPage, immediateAndOnly);
            requestLayout();
        }
    }

    // Animate the drag view back to the original position
    void animateDragViewToOriginalPosition() {
        if (mDragView != null) {
            AnimatorSet anim = new AnimatorSet();
            anim.setDuration(REORDERING_DROP_REPOSITION_DURATION);
            anim.playTogether(
                    ObjectAnimator.ofFloat(mDragView, "translationX", 0f),
                    ObjectAnimator.ofFloat(mDragView, "translationY", 0f));
            anim.addListener(new AnimatorListenerAdapter() {
                @Override
                public void onAnimationEnd(Animator animation) {
                    onPostReorderingAnimationCompleted();
                }
            });
            anim.start();
        }
    }

    // "Zooms out" the PagedView to reveal more side pages
    protected boolean zoomOut() {
        if (mZoomInOutAnim != null && mZoomInOutAnim.isRunning()) {
            mZoomInOutAnim.cancel();
        }

        if (!(getScaleX() < 1f || getScaleY() < 1f)) {
            mZoomInOutAnim = new AnimatorSet();
            mZoomInOutAnim.setDuration(REORDERING_ZOOM_IN_OUT_DURATION);
            mZoomInOutAnim.playTogether(
                    ObjectAnimator.ofFloat(this, "scaleX", mMinScale),
                    ObjectAnimator.ofFloat(this, "scaleY", mMinScale));
            mZoomInOutAnim.addListener(new AnimatorListenerAdapter() {
                @Override
                public void onAnimationStart(Animator animation) {
                    // Show the delete drop target
                    if (mDeleteDropTarget != null) {
                        mDeleteDropTarget.setVisibility(View.VISIBLE);
                        mDeleteDropTarget.animate().alpha(1f)
                            .setDuration(REORDERING_DELETE_DROP_TARGET_FADE_DURATION)
                            .setListener(new AnimatorListenerAdapter() {
                                @Override
                                public void onAnimationStart(Animator animation) {
                                    mDeleteDropTarget.setAlpha(0f);
                                }
                            });
                    }
                }
            });
            mZoomInOutAnim.start();
            return true;
        }
        return false;
    }

    protected void onStartReordering() {
        // Set the touch state to reordering (allows snapping to pages, dragging a child, etc.)
        mTouchState = TOUCH_STATE_REORDERING;
        mIsReordering = true;

        // Mark all the non-widget pages as invisible
        getVisiblePages(mTempVisiblePagesRange);
        boundByReorderablePages(true, mTempVisiblePagesRange);
        for (int i = 0; i < getPageCount(); ++i) {
            if (i < mTempVisiblePagesRange[0] || i > mTempVisiblePagesRange[1]) {
                getPageAt(i).setAlpha(0f);
            }
        }

        // We must invalidate to trigger a redraw to update the layers such that the drag view
        // is always drawn on top
        invalidate();
    }

    private void onPostReorderingAnimationCompleted() {
        // Trigger the callback when reordering has settled
        --mPostReorderingPreZoomInRemainingAnimationCount;
        if (mPostReorderingPreZoomInRunnable != null &&
                mPostReorderingPreZoomInRemainingAnimationCount == 0) {
            mPostReorderingPreZoomInRunnable.run();
            mPostReorderingPreZoomInRunnable = null;
        }
    }

    protected void onEndReordering() {
        mIsReordering = false;

        // Mark all the non-widget pages as visible again
        getVisiblePages(mTempVisiblePagesRange);
        boundByReorderablePages(true, mTempVisiblePagesRange);
        for (int i = 0; i < getPageCount(); ++i) {
            if (i < mTempVisiblePagesRange[0] || i > mTempVisiblePagesRange[1]) {
                getPageAt(i).setAlpha(1f);
            }
        }
    }

    public boolean startReordering() {
        int dragViewIndex = getPageNearestToCenterOfScreen();
        mTempVisiblePagesRange[0] = 0;
        mTempVisiblePagesRange[1] = getPageCount() - 1;
        boundByReorderablePages(true, mTempVisiblePagesRange);
        mReorderingStarted = true;

        // Check if we are within the reordering range
        if (mTempVisiblePagesRange[0] <= dragViewIndex &&
                dragViewIndex <= mTempVisiblePagesRange[1]) {
            if (zoomOut()) {
                // Find the drag view under the pointer
                mDragView = getChildAt(dragViewIndex);

                onStartReordering();
            }
            return true;
        }
        return false;
    }

    boolean isReordering(boolean testTouchState) {
        boolean state = mIsReordering;
        if (testTouchState) {
            state &= (mTouchState == TOUCH_STATE_REORDERING);
        }
        return state;
    }
    void endReordering() {
        // For simplicity, we call endReordering sometimes even if reordering was never started.
        // In that case, we don't want to do anything.
        if (!mReorderingStarted) return;
        mReorderingStarted = false;

        // If we haven't flung-to-delete the current child, then we just animate the drag view
        // back into position
        final Runnable onCompleteRunnable = new Runnable() {
            @Override
            public void run() {
                onEndReordering();
            }
        };
        if (!mDeferringForDelete) {
            mPostReorderingPreZoomInRunnable = new Runnable() {
                public void run() {
                    zoomIn(onCompleteRunnable);
                };
            };

            mPostReorderingPreZoomInRemainingAnimationCount =
                    NUM_ANIMATIONS_RUNNING_BEFORE_ZOOM_OUT;
            // Snap to the current page
            snapToPage(indexOfChild(mDragView), 0);
            // Animate the drag view back to the front position
            animateDragViewToOriginalPosition();
        } else {
            // Handled in post-delete-animation-callbacks
        }
    }

    // "Zooms in" the PagedView to highlight the current page
    protected boolean zoomIn(final Runnable onCompleteRunnable) {
        if (mZoomInOutAnim != null && mZoomInOutAnim.isRunning()) {
            mZoomInOutAnim.cancel();
        }
        if (getScaleX() < 1f || getScaleY() < 1f) {
            mZoomInOutAnim = new AnimatorSet();
            mZoomInOutAnim.setDuration(REORDERING_ZOOM_IN_OUT_DURATION);
            mZoomInOutAnim.playTogether(
                    ObjectAnimator.ofFloat(this, "scaleX", 1f),
                    ObjectAnimator.ofFloat(this, "scaleY", 1f));
            mZoomInOutAnim.addListener(new AnimatorListenerAdapter() {
                @Override
                public void onAnimationStart(Animator animation) {
                    // Hide the delete drop target
                    if (mDeleteDropTarget != null) {
                        mDeleteDropTarget.animate().alpha(0f)
                            .setDuration(REORDERING_DELETE_DROP_TARGET_FADE_DURATION)
                            .setListener(new AnimatorListenerAdapter() {
                                @Override
                                public void onAnimationEnd(Animator animation) {
                                    mDeleteDropTarget.setVisibility(View.GONE);
                                }
                            });
                    }
                }
                @Override
                public void onAnimationCancel(Animator animation) {
                    mDragView = null;
                }
                @Override
                public void onAnimationEnd(Animator animation) {
                    mDragView = null;
                    if (onCompleteRunnable != null) {
                        onCompleteRunnable.run();
                    }
                }
            });
            mZoomInOutAnim.start();
            return true;
        } else {
            if (onCompleteRunnable != null) {
                onCompleteRunnable.run();
            }
        }
        return false;
    }

    /*
     * Flinging to delete - IN PROGRESS
     */
    private PointF isFlingingToDelete() {
        ViewConfiguration config = ViewConfiguration.get(getContext());
        mVelocityTracker.computeCurrentVelocity(1000, config.getScaledMaximumFlingVelocity());

        if (mVelocityTracker.getYVelocity() < mFlingToDeleteThresholdVelocity) {
            // Do a quick dot product test to ensure that we are flinging upwards
            PointF vel = new PointF(mVelocityTracker.getXVelocity(),
                    mVelocityTracker.getYVelocity());
            PointF upVec = new PointF(0f, -1f);
            float theta = (float) Math.acos(((vel.x * upVec.x) + (vel.y * upVec.y)) /
                    (vel.length() * upVec.length()));
            if (theta <= Math.toRadians(FLING_TO_DELETE_MAX_FLING_DEGREES)) {
                return vel;
            }
        }
        return null;
    }

    /**
     * Creates an animation from the current drag view along its current velocity vector.
     * For this animation, the alpha runs for a fixed duration and we update the position
     * progressively.
     */
    private static class FlingAlongVectorAnimatorUpdateListener implements AnimatorUpdateListener {
        private View mDragView;
        private PointF mVelocity;
        private Rect mFrom;
        private long mPrevTime;
        private float mFriction;

        private final TimeInterpolator mAlphaInterpolator = new DecelerateInterpolator(0.75f);

        public FlingAlongVectorAnimatorUpdateListener(View dragView, PointF vel, Rect from,
                long startTime, float friction) {
            mDragView = dragView;
            mVelocity = vel;
            mFrom = from;
            mPrevTime = startTime;
            mFriction = 1f - (mDragView.getResources().getDisplayMetrics().density * friction);
        }

        @Override
        public void onAnimationUpdate(ValueAnimator animation) {
            float t = ((Float) animation.getAnimatedValue()).floatValue();
            long curTime = AnimationUtils.currentAnimationTimeMillis();

            mFrom.left += (mVelocity.x * (curTime - mPrevTime) / 1000f);
            mFrom.top += (mVelocity.y * (curTime - mPrevTime) / 1000f);

            mDragView.setTranslationX(mFrom.left);
            mDragView.setTranslationY(mFrom.top);
            mDragView.setAlpha(1f - mAlphaInterpolator.getInterpolation(t));

            mVelocity.x *= mFriction;
            mVelocity.y *= mFriction;
            mPrevTime = curTime;
        }
    };

    private static final int ANIM_TAG_KEY = 100;

    private Runnable createPostDeleteAnimationRunnable(final View dragView) {
        return new Runnable() {
            @Override
            public void run() {
                int dragViewIndex = indexOfChild(dragView);

                // For each of the pages around the drag view, animate them from the previous
                // position to the new position in the layout (as a result of the drag view moving
                // in the layout)
                // NOTE: We can make an assumption here because we have side-bound pages that we
                //       will always have pages to animate in from the left
                getVisiblePages(mTempVisiblePagesRange);
                boundByReorderablePages(true, mTempVisiblePagesRange);
                boolean isLastWidgetPage = (mTempVisiblePagesRange[0] == mTempVisiblePagesRange[1]);
                boolean slideFromLeft = (isLastWidgetPage ||
                        dragViewIndex > mTempVisiblePagesRange[0]);

                // Setup the scroll to the correct page before we swap the views
                if (slideFromLeft) {
                    snapToPageImmediately(dragViewIndex - 1);
                }

                int firstIndex = (isLastWidgetPage ? 0 : mTempVisiblePagesRange[0]);
                int lastIndex = Math.min(mTempVisiblePagesRange[1], getPageCount() - 1);
                int lowerIndex = (slideFromLeft ? firstIndex : dragViewIndex + 1 );
                int upperIndex = (slideFromLeft ? dragViewIndex - 1 : lastIndex);
                ArrayList<Animator> animations = new ArrayList<Animator>();
                for (int i = lowerIndex; i <= upperIndex; ++i) {
                    View v = getChildAt(i);
                    // dragViewIndex < pageUnderPointIndex, so after we remove the
                    // drag view all subsequent views to pageUnderPointIndex will
                    // shift down.
                    int oldX = 0;
                    int newX = 0;
                    if (slideFromLeft) {
                        if (i == 0) {
                            // Simulate the page being offscreen with the page spacing
                            oldX = getViewportOffsetX() + getChildOffset(i) - getChildWidth(i)
                                    - mPageSpacing;
                        } else {
                            oldX = getViewportOffsetX() + getChildOffset(i - 1);
                        }
                        newX = getViewportOffsetX() + getChildOffset(i);
                    } else {
                        oldX = getChildOffset(i) - getChildOffset(i - 1);
                        newX = 0;
                    }

                    // Animate the view translation from its old position to its new
                    // position
                    AnimatorSet anim = (AnimatorSet) v.getTag();
                    if (anim != null) {
                        anim.cancel();
                    }

                    // Note: Hacky, but we want to skip any optimizations to not draw completely
                    // hidden views
                    v.setAlpha(Math.max(v.getAlpha(), 0.01f));
                    v.setTranslationX(oldX - newX);
                    anim = new AnimatorSet();
                    anim.playTogether(
                            ObjectAnimator.ofFloat(v, "translationX", 0f),
                            ObjectAnimator.ofFloat(v, "alpha", 1f));
                    animations.add(anim);
                    v.setTag(ANIM_TAG_KEY, anim);
                }

                AnimatorSet slideAnimations = new AnimatorSet();
                slideAnimations.playTogether(animations);
                slideAnimations.setDuration(DELETE_SLIDE_IN_SIDE_PAGE_DURATION);
                slideAnimations.addListener(new AnimatorListenerAdapter() {
                    @Override
                    public void onAnimationEnd(Animator animation) {
                        final Runnable onCompleteRunnable = new Runnable() {
                            @Override
                            public void run() {
                                mDeferringForDelete = false;
                                onEndReordering();
                                onRemoveViewAnimationCompleted();
                            }
                        };
                        zoomIn(onCompleteRunnable);
                    }
                });
                slideAnimations.start();

                removeView(dragView);
                onRemoveView(dragView, true);
            }
        };
    }

    public void onFlingToDelete(PointF vel) {
        final long startTime = AnimationUtils.currentAnimationTimeMillis();

        // NOTE: Because it takes time for the first frame of animation to actually be
        // called and we expect the animation to be a continuation of the fling, we have
        // to account for the time that has elapsed since the fling finished.  And since
        // we don't have a startDelay, we will always get call to update when we call
        // start() (which we want to ignore).
        final TimeInterpolator tInterpolator = new TimeInterpolator() {
            private int mCount = -1;
            private long mStartTime;
            private float mOffset;
            /* Anonymous inner class ctor */ {
                mStartTime = startTime;
            }

            @Override
            public float getInterpolation(float t) {
                if (mCount < 0) {
                    mCount++;
                } else if (mCount == 0) {
                    mOffset = Math.min(0.5f, (float) (AnimationUtils.currentAnimationTimeMillis() -
                            mStartTime) / FLING_TO_DELETE_FADE_OUT_DURATION);
                    mCount++;
                }
                return Math.min(1f, mOffset + t);
            }
        };

        final Rect from = new Rect();
        final View dragView = mDragView;
        from.left = (int) dragView.getTranslationX();
        from.top = (int) dragView.getTranslationY();
        AnimatorUpdateListener updateCb = new FlingAlongVectorAnimatorUpdateListener(dragView, vel,
                from, startTime, FLING_TO_DELETE_FRICTION);

        final Runnable onAnimationEndRunnable = createPostDeleteAnimationRunnable(dragView);

        // Create and start the animation
        ValueAnimator mDropAnim = new ValueAnimator();
        mDropAnim.setInterpolator(tInterpolator);
        mDropAnim.setDuration(FLING_TO_DELETE_FADE_OUT_DURATION);
        mDropAnim.setFloatValues(0f, 1f);
        mDropAnim.addUpdateListener(updateCb);
        mDropAnim.addListener(new AnimatorListenerAdapter() {
            public void onAnimationEnd(Animator animation) {
                onAnimationEndRunnable.run();
            }
        });
        mDropAnim.start();
        mDeferringForDelete = true;
    }

    /* Drag to delete */
    private boolean isHoveringOverDeleteDropTarget(int x, int y) {
        if (mDeleteDropTarget != null) {
            mAltTmpRect.set(0, 0, 0, 0);
            View parent = (View) mDeleteDropTarget.getParent();
            if (parent != null) {
                parent.getGlobalVisibleRect(mAltTmpRect);
            }
            mDeleteDropTarget.getGlobalVisibleRect(mTmpRect);
            mTmpRect.offset(-mAltTmpRect.left, -mAltTmpRect.top);
            return mTmpRect.contains(x, y);
        }
        return false;
    }

    protected void setPageHoveringOverDeleteDropTarget(int viewIndex, boolean isHovering) {}

    private void onDropToDelete() {
        final View dragView = mDragView;

        final float toScale = 0f;
        final float toAlpha = 0f;

        // Create and start the complex animation
        ArrayList<Animator> animations = new ArrayList<Animator>();
        AnimatorSet motionAnim = new AnimatorSet();
        motionAnim.setInterpolator(new DecelerateInterpolator(2));
        motionAnim.playTogether(
                ObjectAnimator.ofFloat(dragView, "scaleX", toScale),
                ObjectAnimator.ofFloat(dragView, "scaleY", toScale));
        animations.add(motionAnim);

        AnimatorSet alphaAnim = new AnimatorSet();
        alphaAnim.setInterpolator(new LinearInterpolator());
        alphaAnim.playTogether(
                ObjectAnimator.ofFloat(dragView, "alpha", toAlpha));
        animations.add(alphaAnim);

        final Runnable onAnimationEndRunnable = createPostDeleteAnimationRunnable(dragView);

        AnimatorSet anim = new AnimatorSet();
        anim.playTogether(animations);
        anim.setDuration(DRAG_TO_DELETE_FADE_OUT_DURATION);
        anim.addListener(new AnimatorListenerAdapter() {
            public void onAnimationEnd(Animator animation) {
                onAnimationEndRunnable.run();
            }
        });
        anim.start();

        mDeferringForDelete = true;
    }

    /* Accessibility */
    @Override
    public void onInitializeAccessibilityNodeInfo(AccessibilityNodeInfo info) {
        super.onInitializeAccessibilityNodeInfo(info);
        info.setScrollable(getPageCount() > 1);
        if (getCurrentPage() < getPageCount() - 1) {
            info.addAction(AccessibilityNodeInfo.ACTION_SCROLL_FORWARD);
        }
        if (getCurrentPage() > 0) {
            info.addAction(AccessibilityNodeInfo.ACTION_SCROLL_BACKWARD);
        }
    }

    @Override
    public void onInitializeAccessibilityEvent(AccessibilityEvent event) {
        super.onInitializeAccessibilityEvent(event);
        event.setScrollable(true);
        if (event.getEventType() == AccessibilityEvent.TYPE_VIEW_SCROLLED) {
            event.setFromIndex(mCurrentPage);
            event.setToIndex(mCurrentPage);
            event.setItemCount(getChildCount());
        }
    }

    @Override
    public boolean performAccessibilityAction(int action, Bundle arguments) {
        if (super.performAccessibilityAction(action, arguments)) {
            return true;
        }
        switch (action) {
            case AccessibilityNodeInfo.ACTION_SCROLL_FORWARD: {
                if (getCurrentPage() < getPageCount() - 1) {
                    scrollRight();
                    return true;
                }
            } break;
            case AccessibilityNodeInfo.ACTION_SCROLL_BACKWARD: {
                if (getCurrentPage() > 0) {
                    scrollLeft();
                    return true;
                }
            } break;
        }
        return false;
    }

    protected String getCurrentPageDescription() {
        return String.format(getContext().getString(R.string.default_scroll_format),
                getNextPage() + 1, getChildCount());
    }

    @Override
    public boolean onHoverEvent(android.view.MotionEvent event) {
        return true;
    }
}