src/com/android/launcher3/LauncherRootView.java

package com.android.launcher3;

import android.annotation.TargetApi;
import android.app.ActivityManager;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewDebug;

import static com.android.launcher3.util.SystemUiController.FLAG_DARK_NAV;
import static com.android.launcher3.util.SystemUiController.UI_STATE_ROOT_VIEW;

public class LauncherRootView extends InsettableFrameLayout {

    private final Launcher mLauncher;

    private final Paint mOpaquePaint;
    @ViewDebug.ExportedProperty(category = "launcher")
    private boolean mDrawSideInsetBar;
    @ViewDebug.ExportedProperty(category = "launcher")
    private int mLeftInsetBarWidth;
    @ViewDebug.ExportedProperty(category = "launcher")
    private int mRightInsetBarWidth;

    private View mAlignedView;

    public LauncherRootView(Context context, AttributeSet attrs) {
        super(context, attrs);

        mOpaquePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mOpaquePaint.setColor(Color.BLACK);
        mOpaquePaint.setStyle(Paint.Style.FILL);

        mLauncher = Launcher.getLauncher(context);
    }

    @Override
    protected void onFinishInflate() {
        if (getChildCount() > 0) {
            // LauncherRootView contains only one child, which should be aligned
            // based on the horizontal insets.
            mAlignedView = getChildAt(0);
        }
        super.onFinishInflate();
    }

    @TargetApi(23)
    @Override
    protected boolean fitSystemWindows(Rect insets) {
        mDrawSideInsetBar = (insets.right > 0 || insets.left > 0) &&
                (!Utilities.ATLEAST_MARSHMALLOW ||
                        getContext().getSystemService(ActivityManager.class).isLowRamDevice());
        if (mDrawSideInsetBar) {
            mLeftInsetBarWidth = insets.left;
            mRightInsetBarWidth = insets.right;
            insets = new Rect(0, insets.top, 0, insets.bottom);
        } else {
            mLeftInsetBarWidth = mRightInsetBarWidth = 0;
        }
        mLauncher.getSystemUiController().updateUiState(
                UI_STATE_ROOT_VIEW, mDrawSideInsetBar ? FLAG_DARK_NAV : 0);

        // Update device profile before notifying th children.
        mLauncher.getDeviceProfile().updateInsets(insets);
        setInsets(insets);

        if (mAlignedView != null) {
            // Apply margins on aligned view to handle left/right insets.
            MarginLayoutParams lp = (MarginLayoutParams) mAlignedView.getLayoutParams();
            if (lp.leftMargin != mLeftInsetBarWidth || lp.rightMargin != mRightInsetBarWidth) {
                lp.leftMargin = mLeftInsetBarWidth;
                lp.rightMargin = mRightInsetBarWidth;
                mAlignedView.setLayoutParams(lp);
            }
        }

        return true; // I'll take it from here
    }

    public void dispatchInsets() {
        fitSystemWindows(mInsets);
    }

    @Override
    protected void dispatchDraw(Canvas canvas) {
        super.dispatchDraw(canvas);

        // If the right inset is opaque, draw a black rectangle to ensure that is stays opaque.
        if (mDrawSideInsetBar) {
            if (mRightInsetBarWidth > 0) {
                int width = getWidth();
                canvas.drawRect(width - mRightInsetBarWidth, 0, width, getHeight(), mOpaquePaint);
            }
            if (mLeftInsetBarWidth > 0) {
                canvas.drawRect(0, 0, mLeftInsetBarWidth, getHeight(), mOpaquePaint);
            }
        }
    }
}