android/launcher2/DragLayer.java

/*
 * Copyright (C) 2008 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.launcher2;

import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.animation.TimeInterpolator;
import android.animation.ValueAnimator;
import android.animation.ValueAnimator.AnimatorUpdateListener;
import android.content.Context;
import android.content.res.Resources;
import android.graphics.Canvas;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffColorFilter;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.util.AttributeSet;
import android.view.KeyEvent;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.view.ViewParent;
import android.view.accessibility.AccessibilityEvent;
import android.view.accessibility.AccessibilityManager;
import android.view.animation.DecelerateInterpolator;
import android.view.animation.Interpolator;
import android.widget.FrameLayout;
import android.widget.TextView;

import com.android.launcher.R;

import java.util.ArrayList;

/**
 * A ViewGroup that coordinates dragging across its descendants
 */
public class DragLayer extends FrameLayout implements ViewGroup.OnHierarchyChangeListener {
    private DragController mDragController;
    private int[] mTmpXY = new int[2];

    private int mXDown, mYDown;
    private Launcher mLauncher;

    // Variables relating to resizing widgets
    private final ArrayList<AppWidgetResizeFrame> mResizeFrames =
            new ArrayList<AppWidgetResizeFrame>();
    private AppWidgetResizeFrame mCurrentResizeFrame;

    // Variables relating to animation of views after drop
    private ValueAnimator mDropAnim = null;
    private ValueAnimator mFadeOutAnim = null;
    private TimeInterpolator mCubicEaseOutInterpolator = new DecelerateInterpolator(1.5f);
    private DragView mDropView = null;
    private int mAnchorViewInitialScrollX = 0;
    private View mAnchorView = null;

    private boolean mHoverPointClosesFolder = false;
    private Rect mHitRect = new Rect();
    private int mWorkspaceIndex = -1;
    private int mQsbIndex = -1;
    public static final int ANIMATION_END_DISAPPEAR = 0;
    public static final int ANIMATION_END_FADE_OUT = 1;
    public static final int ANIMATION_END_REMAIN_VISIBLE = 2;

    /**
     * Used to create a new DragLayer from XML.
     *
     * @param context The application's context.
     * @param attrs The attributes set containing the Workspace's customization values.
     */
    public DragLayer(Context context, AttributeSet attrs) {
        super(context, attrs);

        // Disable multitouch across the workspace/all apps/customize tray
        setMotionEventSplittingEnabled(false);
        setChildrenDrawingOrderEnabled(true);
        setOnHierarchyChangeListener(this);

        mLeftHoverDrawable = getResources().getDrawable(R.drawable.page_hover_left_holo);
        mRightHoverDrawable = getResources().getDrawable(R.drawable.page_hover_right_holo);
    }

    public void setup(Launcher launcher, DragController controller) {
        mLauncher = launcher;
        mDragController = controller;
    }

    @Override
    public boolean dispatchKeyEvent(KeyEvent event) {
        return mDragController.dispatchKeyEvent(event) || super.dispatchKeyEvent(event);
    }

    private boolean isEventOverFolderTextRegion(Folder folder, MotionEvent ev) {
        getDescendantRectRelativeToSelf(folder.getEditTextRegion(), mHitRect);
        if (mHitRect.contains((int) ev.getX(), (int) ev.getY())) {
            return true;
        }
        return false;
    }

    private boolean isEventOverFolder(Folder folder, MotionEvent ev) {
        getDescendantRectRelativeToSelf(folder, mHitRect);
        if (mHitRect.contains((int) ev.getX(), (int) ev.getY())) {
            return true;
        }
        return false;
    }

    private boolean handleTouchDown(MotionEvent ev, boolean intercept) {
        Rect hitRect = new Rect();
        int x = (int) ev.getX();
        int y = (int) ev.getY();

        for (AppWidgetResizeFrame child: mResizeFrames) {
            child.getHitRect(hitRect);
            if (hitRect.contains(x, y)) {
                if (child.beginResizeIfPointInRegion(x - child.getLeft(), y - child.getTop())) {
                    mCurrentResizeFrame = child;
                    mXDown = x;
                    mYDown = y;
                    requestDisallowInterceptTouchEvent(true);
                    return true;
                }
            }
        }

        Folder currentFolder = mLauncher.getWorkspace().getOpenFolder();
        if (currentFolder != null && !mLauncher.isFolderClingVisible() && intercept) {
            if (currentFolder.isEditingName()) {
                if (!isEventOverFolderTextRegion(currentFolder, ev)) {
                    currentFolder.dismissEditingName();
                    return true;
                }
            }

            getDescendantRectRelativeToSelf(currentFolder, hitRect);
            if (!isEventOverFolder(currentFolder, ev)) {
                mLauncher.closeFolder();
                return true;
            }
        }
        return false;
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        if (ev.getAction() == MotionEvent.ACTION_DOWN) {
            if (handleTouchDown(ev, true)) {
                return true;
            }
        }
        clearAllResizeFrames();
        return mDragController.onInterceptTouchEvent(ev);
    }

    @Override
    public boolean onInterceptHoverEvent(MotionEvent ev) {
        Folder currentFolder = mLauncher.getWorkspace().getOpenFolder();
        if (currentFolder == null) {
            return false;
        } else {
                AccessibilityManager accessibilityManager = (AccessibilityManager)
                        getContext().getSystemService(Context.ACCESSIBILITY_SERVICE);
            if (accessibilityManager.isTouchExplorationEnabled()) {
                final int action = ev.getAction();
                boolean isOverFolder;
                switch (action) {
                    case MotionEvent.ACTION_HOVER_ENTER:
                        isOverFolder = isEventOverFolder(currentFolder, ev);
                        if (!isOverFolder) {
                            sendTapOutsideFolderAccessibilityEvent(currentFolder.isEditingName());
                            mHoverPointClosesFolder = true;
                            return true;
                        } else if (isOverFolder) {
                            mHoverPointClosesFolder = false;
                        } else {
                            return true;
                        }
                    case MotionEvent.ACTION_HOVER_MOVE:
                        isOverFolder = isEventOverFolder(currentFolder, ev);
                        if (!isOverFolder && !mHoverPointClosesFolder) {
                            sendTapOutsideFolderAccessibilityEvent(currentFolder.isEditingName());
                            mHoverPointClosesFolder = true;
                            return true;
                        } else if (isOverFolder) {
                            mHoverPointClosesFolder = false;
                        } else {
                            return true;
                        }
                }
            }
        }
        return false;
    }

    private void sendTapOutsideFolderAccessibilityEvent(boolean isEditingName) {
        AccessibilityManager accessibilityManager = (AccessibilityManager)
                getContext().getSystemService(Context.ACCESSIBILITY_SERVICE);
        if (accessibilityManager.isEnabled()) {
            int stringId = isEditingName ? R.string.folder_tap_to_rename : R.string.folder_tap_to_close;
            AccessibilityEvent event = AccessibilityEvent.obtain(
                    AccessibilityEvent.TYPE_VIEW_FOCUSED);
            onInitializeAccessibilityEvent(event);
            event.getText().add(getContext().getString(stringId));
            accessibilityManager.sendAccessibilityEvent(event);
        }
    }

    @Override
    public boolean onHoverEvent(MotionEvent ev) {
        // If we've received this, we've already done the necessary handling
        // in onInterceptHoverEvent. Return true to consume the event.
        return false;
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        boolean handled = false;
        int action = ev.getAction();

        int x = (int) ev.getX();
        int y = (int) ev.getY();

        if (ev.getAction() == MotionEvent.ACTION_DOWN) {
            if (ev.getAction() == MotionEvent.ACTION_DOWN) {
                if (handleTouchDown(ev, false)) {
                    return true;
                }
            }
        }

        if (mCurrentResizeFrame != null) {
            handled = true;
            switch (action) {
                case MotionEvent.ACTION_MOVE:
                    mCurrentResizeFrame.visualizeResizeForDelta(x - mXDown, y - mYDown);
                    break;
                case MotionEvent.ACTION_CANCEL:
                case MotionEvent.ACTION_UP:
                    mCurrentResizeFrame.visualizeResizeForDelta(x - mXDown, y - mYDown);
                    mCurrentResizeFrame.onTouchUp();
                    mCurrentResizeFrame = null;
            }
        }
        if (handled) return true;
        return mDragController.onTouchEvent(ev);
    }

    /**
     * Determine the rect of the descendant in this DragLayer's coordinates
     *
     * @param descendant The descendant whose coordinates we want to find.
     * @param r The rect into which to place the results.
     * @return The factor by which this descendant is scaled relative to this DragLayer.
     */
    public float getDescendantRectRelativeToSelf(View descendant, Rect r) {
        mTmpXY[0] = 0;
        mTmpXY[1] = 0;
        float scale = getDescendantCoordRelativeToSelf(descendant, mTmpXY);
        r.set(mTmpXY[0], mTmpXY[1],
                mTmpXY[0] + descendant.getWidth(), mTmpXY[1] + descendant.getHeight());
        return scale;
    }

    public void getLocationInDragLayer(View child, int[] loc) {
        loc[0] = 0;
        loc[1] = 0;
        getDescendantCoordRelativeToSelf(child, loc);
    }

    /**
     * Given a coordinate relative to the descendant, find the coordinate in this DragLayer's
     * coordinates.
     *
     * @param descendant The descendant to which the passed coordinate is relative.
     * @param coord The coordinate that we want mapped.
     * @return The factor by which this descendant is scaled relative to this DragLayer.
     */
    public float getDescendantCoordRelativeToSelf(View descendant, int[] coord) {
        float scale = 1.0f;
        float[] pt = {coord[0], coord[1]};
        descendant.getMatrix().mapPoints(pt);
        scale *= descendant.getScaleX();
        pt[0] += descendant.getLeft();
        pt[1] += descendant.getTop();
        ViewParent viewParent = descendant.getParent();
        while (viewParent instanceof View && viewParent != this) {
            final View view = (View)viewParent;
            view.getMatrix().mapPoints(pt);
            scale *= view.getScaleX();
            pt[0] += view.getLeft() - view.getScrollX();
            pt[1] += view.getTop() - view.getScrollY();
            viewParent = view.getParent();
        }
        coord[0] = (int) Math.round(pt[0]);
        coord[1] = (int) Math.round(pt[1]);
        return scale;
    }

    public void getViewRectRelativeToSelf(View v, Rect r) {
        int[] loc = new int[2];
        getLocationInWindow(loc);
        int x = loc[0];
        int y = loc[1];

        v.getLocationInWindow(loc);
        int vX = loc[0];
        int vY = loc[1];

        int left = vX - x;
        int top = vY - y;
        r.set(left, top, left + v.getMeasuredWidth(), top + v.getMeasuredHeight());
    }

    @Override
    public boolean dispatchUnhandledMove(View focused, int direction) {
        return mDragController.dispatchUnhandledMove(focused, direction);
    }

    public static class LayoutParams extends FrameLayout.LayoutParams {
        public int x, y;
        public boolean customPosition = false;

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

        public void setWidth(int width) {
            this.width = width;
        }

        public int getWidth() {
            return width;
        }

        public void setHeight(int height) {
            this.height = height;
        }

        public int getHeight() {
            return height;
        }

        public void setX(int x) {
            this.x = x;
        }

        public int getX() {
            return x;
        }

        public void setY(int y) {
            this.y = y;
        }

        public int getY() {
            return y;
        }
    }

    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);
        int count = getChildCount();
        for (int i = 0; i < count; i++) {
            View child = getChildAt(i);
            final FrameLayout.LayoutParams flp = (FrameLayout.LayoutParams) child.getLayoutParams();
            if (flp instanceof LayoutParams) {
                final LayoutParams lp = (LayoutParams) flp;
                if (lp.customPosition) {
                    child.layout(lp.x, lp.y, lp.x + lp.width, lp.y + lp.height);
                }
            }
        }
    }

    public void clearAllResizeFrames() {
        if (mResizeFrames.size() > 0) {
            for (AppWidgetResizeFrame frame: mResizeFrames) {
                frame.commitResize();
                removeView(frame);
            }
            mResizeFrames.clear();
        }
    }

    public boolean hasResizeFrames() {
        return mResizeFrames.size() > 0;
    }

    public boolean isWidgetBeingResized() {
        return mCurrentResizeFrame != null;
    }

    public void addResizeFrame(ItemInfo itemInfo, LauncherAppWidgetHostView widget,
            CellLayout cellLayout) {
        AppWidgetResizeFrame resizeFrame = new AppWidgetResizeFrame(getContext(),
                widget, cellLayout, this);

        LayoutParams lp = new LayoutParams(-1, -1);
        lp.customPosition = true;

        addView(resizeFrame, lp);
        mResizeFrames.add(resizeFrame);

        resizeFrame.snapToWidget(false);
    }

    public void animateViewIntoPosition(DragView dragView, final View child) {
        animateViewIntoPosition(dragView, child, null);
    }

    public void animateViewIntoPosition(DragView dragView, final int[] pos, float alpha,
            float scaleX, float scaleY, int animationEndStyle, Runnable onFinishRunnable,
            int duration) {
        Rect r = new Rect();
        getViewRectRelativeToSelf(dragView, r);
        final int fromX = r.left;
        final int fromY = r.top;

        animateViewIntoPosition(dragView, fromX, fromY, pos[0], pos[1], alpha, 1, 1, scaleX, scaleY,
                onFinishRunnable, animationEndStyle, duration, null);
    }

    public void animateViewIntoPosition(DragView dragView, final View child,
            final Runnable onFinishAnimationRunnable) {
        animateViewIntoPosition(dragView, child, -1, onFinishAnimationRunnable, null);
    }

    public void animateViewIntoPosition(DragView dragView, final View child, int duration,
            final Runnable onFinishAnimationRunnable, View anchorView) {
        ShortcutAndWidgetContainer parentChildren = (ShortcutAndWidgetContainer) child.getParent();
        CellLayout parent = (CellLayout) (CellLayout) parentChildren.getParent();
        CellLayout.LayoutParams lp =  (CellLayout.LayoutParams) child.getLayoutParams();
        parentChildren.measureChild(child);

        Rect r = new Rect();
        getViewRectRelativeToSelf(dragView, r);

        int coord[] = new int[2];
        coord[0] = lp.x;
        coord[1] = lp.y;

        // Since the child hasn't necessarily been laid out, we force the lp to be updated with
        // the correct coordinates (above) and use these to determine the final location
        float scale = getDescendantCoordRelativeToSelf((View) child.getParent(), coord);
        int toX = coord[0];
        int toY = coord[1];
        if (child instanceof TextView) {
            TextView tv = (TextView) child;

            // The child may be scaled (always about the center of the view) so to account for it,
            // we have to offset the position by the scaled size.  Once we do that, we can center
            // the drag view about the scaled child view.
            toY += Math.round(scale * tv.getPaddingTop());
            toY -= dragView.getMeasuredHeight() * (1 - scale) / 2;
            toX -= (dragView.getMeasuredWidth() - Math.round(scale * child.getMeasuredWidth())) / 2;
        } else if (child instanceof FolderIcon) {
            // Account for holographic blur padding on the drag view
            toY -= Workspace.DRAG_BITMAP_PADDING / 2;
            // Center in the x coordinate about the target's drawable
            toX -= (dragView.getMeasuredWidth() - Math.round(scale * child.getMeasuredWidth())) / 2;
        } else {
            toY -= (Math.round(scale * (dragView.getHeight() - child.getMeasuredHeight()))) / 2;
            toX -= (Math.round(scale * (dragView.getMeasuredWidth()
                    - child.getMeasuredWidth()))) / 2;
        }

        final int fromX = r.left;
        final int fromY = r.top;
        child.setVisibility(INVISIBLE);
        Runnable onCompleteRunnable = new Runnable() {
            public void run() {
                child.setVisibility(VISIBLE);
                if (onFinishAnimationRunnable != null) {
                    onFinishAnimationRunnable.run();
                }
            }
        };
        animateViewIntoPosition(dragView, fromX, fromY, toX, toY, 1, 1, 1, scale, scale,
                onCompleteRunnable, ANIMATION_END_DISAPPEAR, duration, anchorView);
    }

    public void animateViewIntoPosition(final DragView view, final int fromX, final int fromY,
            final int toX, final int toY, float finalAlpha, float initScaleX, float initScaleY,
            float finalScaleX, float finalScaleY, Runnable onCompleteRunnable,
            int animationEndStyle, int duration, View anchorView) {
        Rect from = new Rect(fromX, fromY, fromX +
                view.getMeasuredWidth(), fromY + view.getMeasuredHeight());
        Rect to = new Rect(toX, toY, toX + view.getMeasuredWidth(), toY + view.getMeasuredHeight());
        animateView(view, from, to, finalAlpha, initScaleX, initScaleY, finalScaleX, finalScaleY, duration,
                null, null, onCompleteRunnable, animationEndStyle, anchorView);
    }

    /**
     * This method animates a view at the end of a drag and drop animation.
     *
     * @param view The view to be animated. This view is drawn directly into DragLayer, and so
     *        doesn't need to be a child of DragLayer.
     * @param from The initial location of the view. Only the left and top parameters are used.
     * @param to The final location of the view. Only the left and top parameters are used. This
     *        location doesn't account for scaling, and so should be centered about the desired
     *        final location (including scaling).
     * @param finalAlpha The final alpha of the view, in case we want it to fade as it animates.
     * @param finalScale The final scale of the view. The view is scaled about its center.
     * @param duration The duration of the animation.
     * @param motionInterpolator The interpolator to use for the location of the view.
     * @param alphaInterpolator The interpolator to use for the alpha of the view.
     * @param onCompleteRunnable Optional runnable to run on animation completion.
     * @param fadeOut Whether or not to fade out the view once the animation completes. If true,
     *        the runnable will execute after the view is faded out.
     * @param anchorView If not null, this represents the view which the animated view stays
     *        anchored to in case scrolling is currently taking place. Note: currently this is
     *        only used for the X dimension for the case of the workspace.
     */
    public void animateView(final DragView view, final Rect from, final Rect to,
            final float finalAlpha, final float initScaleX, final float initScaleY,
            final float finalScaleX, final float finalScaleY, int duration,
            final Interpolator motionInterpolator, final Interpolator alphaInterpolator,
            final Runnable onCompleteRunnable, final int animationEndStyle, View anchorView) {

        // Calculate the duration of the animation based on the object's distance
        final float dist = (float) Math.sqrt(Math.pow(to.left - from.left, 2) +
                Math.pow(to.top - from.top, 2));
        final Resources res = getResources();
        final float maxDist = (float) res.getInteger(R.integer.config_dropAnimMaxDist);

        // If duration < 0, this is a cue to compute the duration based on the distance
        if (duration < 0) {
            duration = res.getInteger(R.integer.config_dropAnimMaxDuration);
            if (dist < maxDist) {
                duration *= mCubicEaseOutInterpolator.getInterpolation(dist / maxDist);
            }
            duration = Math.max(duration, res.getInteger(R.integer.config_dropAnimMinDuration));
        }

        // Fall back to cubic ease out interpolator for the animation if none is specified
        TimeInterpolator interpolator = null;
        if (alphaInterpolator == null || motionInterpolator == null) {
            interpolator = mCubicEaseOutInterpolator;
        }

        // Animate the view
        final float initAlpha = view.getAlpha();
        final float dropViewScale = view.getScaleX();
        AnimatorUpdateListener updateCb = new AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                final float percent = (Float) animation.getAnimatedValue();
                final int width = view.getMeasuredWidth();
                final int height = view.getMeasuredHeight();

                float alphaPercent = alphaInterpolator == null ? percent :
                        alphaInterpolator.getInterpolation(percent);
                float motionPercent = motionInterpolator == null ? percent :
                        motionInterpolator.getInterpolation(percent);

                float initialScaleX = initScaleX * dropViewScale;
                float initialScaleY = initScaleY * dropViewScale;
                float scaleX = finalScaleX * percent + initialScaleX * (1 - percent);
                float scaleY = finalScaleY * percent + initialScaleY * (1 - percent);
                float alpha = finalAlpha * alphaPercent + initAlpha * (1 - alphaPercent);

                float fromLeft = from.left + (initialScaleX - 1f) * width / 2;
                float fromTop = from.top + (initialScaleY - 1f) * height / 2;

                int x = (int) (fromLeft + Math.round(((to.left - fromLeft) * motionPercent)));
                int y = (int) (fromTop + Math.round(((to.top - fromTop) * motionPercent)));

                int xPos = x - mDropView.getScrollX() + (mAnchorView != null
                        ? (mAnchorViewInitialScrollX - mAnchorView.getScrollX()) : 0);
                int yPos = y - mDropView.getScrollY();

                mDropView.setTranslationX(xPos);
                mDropView.setTranslationY(yPos);
                mDropView.setScaleX(scaleX);
                mDropView.setScaleY(scaleY);
                mDropView.setAlpha(alpha);
            }
        };
        animateView(view, updateCb, duration, interpolator, onCompleteRunnable, animationEndStyle,
                anchorView);
    }

    public void animateView(final DragView view, AnimatorUpdateListener updateCb, int duration,
            TimeInterpolator interpolator, final Runnable onCompleteRunnable,
            final int animationEndStyle, View anchorView) {
        // Clean up the previous animations
        if (mDropAnim != null) mDropAnim.cancel();
        if (mFadeOutAnim != null) mFadeOutAnim.cancel();

        // Show the drop view if it was previously hidden
        mDropView = view;
        mDropView.cancelAnimation();
        mDropView.resetLayoutParams();

        // Set the anchor view if the page is scrolling
        if (anchorView != null) {
            mAnchorViewInitialScrollX = anchorView.getScrollX();
        }
        mAnchorView = anchorView;

        // Create and start the animation
        mDropAnim = new ValueAnimator();
        mDropAnim.setInterpolator(interpolator);
        mDropAnim.setDuration(duration);
        mDropAnim.setFloatValues(0f, 1f);
        mDropAnim.addUpdateListener(updateCb);
        mDropAnim.addListener(new AnimatorListenerAdapter() {
            public void onAnimationEnd(Animator animation) {
                if (onCompleteRunnable != null) {
                    onCompleteRunnable.run();
                }
                switch (animationEndStyle) {
                case ANIMATION_END_DISAPPEAR:
                    clearAnimatedView();
                    break;
                case ANIMATION_END_FADE_OUT:
                    fadeOutDragView();
                    break;
                case ANIMATION_END_REMAIN_VISIBLE:
                    break;
                }
            }
        });
        mDropAnim.start();
    }

    public void clearAnimatedView() {
        if (mDropAnim != null) {
            mDropAnim.cancel();
        }
        if (mDropView != null) {
            mDragController.onDeferredEndDrag(mDropView);
        }
        mDropView = null;
        invalidate();
    }

    public View getAnimatedView() {
        return mDropView;
    }

    private void fadeOutDragView() {
        mFadeOutAnim = new ValueAnimator();
        mFadeOutAnim.setDuration(150);
        mFadeOutAnim.setFloatValues(0f, 1f);
        mFadeOutAnim.removeAllUpdateListeners();
        mFadeOutAnim.addUpdateListener(new AnimatorUpdateListener() {
            public void onAnimationUpdate(ValueAnimator animation) {
                final float percent = (Float) animation.getAnimatedValue();

                float alpha = 1 - percent;
                mDropView.setAlpha(alpha);
            }
        });
        mFadeOutAnim.addListener(new AnimatorListenerAdapter() {
            public void onAnimationEnd(Animator animation) {
                if (mDropView != null) {
                    mDragController.onDeferredEndDrag(mDropView);
                }
                mDropView = null;
                invalidate();
            }
        });
        mFadeOutAnim.start();
    }

    @Override
    public void onChildViewAdded(View parent, View child) {
        updateChildIndices();
    }

    @Override
    public void onChildViewRemoved(View parent, View child) {
        updateChildIndices();
    }

    private void updateChildIndices() {
        if (mLauncher != null) {
            mWorkspaceIndex = indexOfChild(mLauncher.getWorkspace());
            mQsbIndex = indexOfChild(mLauncher.getSearchBar());
        }
    }

    @Override
    protected int getChildDrawingOrder(int childCount, int i) {
        // We don't want to prioritize the workspace drawing on top of the other children in
        // landscape for the overscroll event.
        if (LauncherApplication.isScreenLandscape(getContext())) {
            return super.getChildDrawingOrder(childCount, i);
        }

        if (mWorkspaceIndex == -1 || mQsbIndex == -1 ||
                mLauncher.getWorkspace().isDrawingBackgroundGradient()) {
            return i;
        }

        // This ensures that the workspace is drawn above the hotseat and qsb,
        // except when the workspace is drawing a background gradient, in which
        // case we want the workspace to stay behind these elements.
        if (i == mQsbIndex) {
            return mWorkspaceIndex;
        } else if (i == mWorkspaceIndex) {
            return mQsbIndex;
        } else {
            return i;
        }
    }

    private boolean mInScrollArea;
    private Drawable mLeftHoverDrawable;
    private Drawable mRightHoverDrawable;

    void onEnterScrollArea(int direction) {
        mInScrollArea = true;
        invalidate();
    }

    void onExitScrollArea() {
        mInScrollArea = false;
        invalidate();
    }

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

        if (mInScrollArea && !LauncherApplication.isScreenLarge()) {
            Workspace workspace = mLauncher.getWorkspace();
            int width = workspace.getWidth();
            Rect childRect = new Rect();
            getDescendantRectRelativeToSelf(workspace.getChildAt(0), childRect);

            int page = workspace.getNextPage();
            CellLayout leftPage = (CellLayout) workspace.getChildAt(page - 1);
            CellLayout rightPage = (CellLayout) workspace.getChildAt(page + 1);

            if (leftPage != null && leftPage.getIsDragOverlapping()) {
                mLeftHoverDrawable.setBounds(0, childRect.top,
                        mLeftHoverDrawable.getIntrinsicWidth(), childRect.bottom);
                mLeftHoverDrawable.draw(canvas);
            } else if (rightPage != null && rightPage.getIsDragOverlapping()) {
                mRightHoverDrawable.setBounds(width - mRightHoverDrawable.getIntrinsicWidth(),
                        childRect.top, width, childRect.bottom);
                mRightHoverDrawable.draw(canvas);
            }
        }
    }
}