src/com/android/launcher3/UninstallDropTarget.java

package com.android.launcher3;

import android.content.ComponentName;
import android.content.Context;
import android.content.Intent;
import android.content.pm.ApplicationInfo;
import android.content.pm.LauncherActivityInfo;
import android.content.pm.PackageManager;
import android.net.Uri;
import android.os.Bundle;
import android.os.UserHandle;
import android.os.UserManager;
import android.util.AttributeSet;
import android.widget.Toast;

import com.android.launcher3.compat.LauncherAppsCompat;

public class UninstallDropTarget extends ButtonDropTarget {

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

    public UninstallDropTarget(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    protected void onFinishInflate() {
        super.onFinishInflate();
        setupUi();
    }

    protected void setupUi() {
        // Get the hover color
        mHoverColor = getResources().getColor(R.color.uninstall_target_hover_tint);
        setDrawable(R.drawable.ic_uninstall_shadow);
    }

    @Override
    protected boolean supportsDrop(DragSource source, ItemInfo info) {
        return supportsDrop(getContext(), info);
    }

    public static boolean supportsDrop(Context context, ItemInfo info) {
        UserManager userManager = (UserManager) context.getSystemService(Context.USER_SERVICE);
        Bundle restrictions = userManager.getUserRestrictions();
        if (restrictions.getBoolean(UserManager.DISALLOW_APPS_CONTROL, false)
                || restrictions.getBoolean(UserManager.DISALLOW_UNINSTALL_APPS, false)) {
            return false;
        }

        return getUninstallTarget(context, info) != null;
    }

    /**
     * @return the component name that should be uninstalled or null.
     */
    private static ComponentName getUninstallTarget(Context context, ItemInfo item) {
        Intent intent = null;
        UserHandle user = null;
        if (item != null &&
                item.itemType == LauncherSettings.BaseLauncherColumns.ITEM_TYPE_APPLICATION) {
            intent = item.getIntent();
            user = item.user;
        }
        if (intent != null) {
            LauncherActivityInfo info = LauncherAppsCompat.getInstance(context)
                    .resolveActivity(intent, user);
            if (info != null
                    && (info.getApplicationInfo().flags & ApplicationInfo.FLAG_SYSTEM) == 0) {
                return info.getComponentName();
            }
        }
        return null;
    }

    @Override
    public void onDrop(DragObject d) {
        // Differ item deletion
        if (d.dragSource instanceof DropTargetSource) {
            ((DropTargetSource) d.dragSource).deferCompleteDropAfterUninstallActivity();
        }
        super.onDrop(d);
    }

    @Override
    public void completeDrop(final DragObject d) {
        DropTargetResultCallback callback = d.dragSource instanceof DropTargetResultCallback
                ? (DropTargetResultCallback) d.dragSource : null;
        startUninstallActivity(mLauncher, d.dragInfo, callback);
    }

    public static boolean startUninstallActivity(Launcher launcher, ItemInfo info) {
        return startUninstallActivity(launcher, info, null);
    }

    public static boolean startUninstallActivity(
            final Launcher launcher, ItemInfo info, DropTargetResultCallback callback) {
        final ComponentName cn = getUninstallTarget(launcher, info);

        final boolean isUninstallable;
        if (cn == null) {
            // System applications cannot be installed. For now, show a toast explaining that.
            // We may give them the option of disabling apps this way.
            Toast.makeText(launcher, R.string.uninstall_system_app_text, Toast.LENGTH_SHORT).show();
            isUninstallable = false;
        } else {
            Intent intent = new Intent(Intent.ACTION_DELETE,
                    Uri.fromParts("package", cn.getPackageName(), cn.getClassName()))
                    .setFlags(Intent.FLAG_ACTIVITY_NEW_TASK
                            | Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS);
            intent.putExtra(Intent.EXTRA_USER, info.user);
            launcher.startActivity(intent);
            isUninstallable = true;
        }
        if (callback != null) {
            sendUninstallResult(launcher, isUninstallable, cn, info.user, callback);
        }
        return isUninstallable;
    }

    /**
     * Notifies the {@param callback} whether the uninstall was successful or not.
     *
     * Since there is no direct callback for an uninstall request, we check the package existence
     * when the launch resumes next time. This assumes that the uninstall activity will finish only
     * after the task is completed
     */
    protected static void sendUninstallResult(
            final Launcher launcher, boolean activityStarted,
            final ComponentName cn, final UserHandle user,
            final DropTargetResultCallback callback) {
        if (activityStarted)  {
            final Runnable checkIfUninstallWasSuccess = new Runnable() {
                @Override
                public void run() {
                    // We use MATCH_UNINSTALLED_PACKAGES as the app can be on SD card as well.
                    boolean uninstallSuccessful = LauncherAppsCompat.getInstance(launcher)
                            .getApplicationInfo(cn.getPackageName(),
                                    PackageManager.MATCH_UNINSTALLED_PACKAGES, user) == null;
                    callback.onDragObjectRemoved(uninstallSuccessful);
                }
            };
            launcher.addOnResumeCallback(checkIfUninstallWasSuccess);
        } else {
            callback.onDragObjectRemoved(false);
        }
    }

    public interface DropTargetResultCallback {
        /**
         * A drag operation was complete.
         * @param isRemoved true if the drag object should be removed, false otherwise.
         */
        void onDragObjectRemoved(boolean isRemoved);
    }

    /**
     * Interface defining an object that can provide uninstallable drag objects.
     */
    public interface DropTargetSource extends DropTargetResultCallback {

        /**
         * Indicates that an uninstall request are made and the actual result may come
         * after some time.
         */
        void deferCompleteDropAfterUninstallActivity();
    }
}