src/com/android/launcher3/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.launcher3;

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.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.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.launcher3.InsettableFrameLayout.LayoutParams;
import com.android.launcher3.util.Thunk;

import java.util.ArrayList;

/**
 * A ViewGroup that coordinates dragging across its descendants
 */
public class DragLayer extends InsettableFrameLayout {
    @Thunk 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);
    @Thunk DragView mDropView = null;
    @Thunk int mAnchorViewInitialScrollX = 0;
    @Thunk View mAnchorView = null;

    private boolean mHoverPointClosesFolder = false;
    private Rect mHitRect = new Rect();
    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;

    private TouchCompleteListener mTouchCompleteListener;

    private View mOverlayView;
    private int mTopViewIndex;
    private int mChildCountOnLastUpdate = -1;

    // Darkening scrim
    private Drawable mBackground;
    private float mBackgroundAlpha = 0;

    // Related to adjacent page hints
    private boolean mInScrollArea;
    private boolean mShowPageHints;
    private Drawable mLeftHoverDrawable;
    private Drawable mRightHoverDrawable;
    private Drawable mLeftHoverDrawableActive;
    private Drawable mRightHoverDrawableActive;

    private boolean mBlockTouches = false;

    /**
     * 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);

        final Resources res = getResources();
        mLeftHoverDrawable = res.getDrawable(R.drawable.page_hover_left);
        mRightHoverDrawable = res.getDrawable(R.drawable.page_hover_right);
        mLeftHoverDrawableActive = res.getDrawable(R.drawable.page_hover_left_active);
        mRightHoverDrawableActive = res.getDrawable(R.drawable.page_hover_right_active);
        mBackground = res.getDrawable(R.drawable.apps_customize_bg);
    }

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

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

    public void showOverlayView(View overlayView) {
        LayoutParams lp = new LayoutParams(LayoutParams.MATCH_PARENT, LayoutParams.MATCH_PARENT);
        mOverlayView = overlayView;
        addView(overlayView, lp);

        // ensure that the overlay view stays on top. we can't use drawing order for this
        // because in API level 16 touch dispatch doesn't respect drawing order.
        mOverlayView.bringToFront();
    }

    public void dismissOverlayView() {
        removeView(mOverlayView);
    }

    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;
    }

    public void setBlockTouch(boolean block) {
        mBlockTouches = block;
    }

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

        if (mBlockTouches) {
            return true;
        }

        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 && 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) {
        int action = ev.getAction();

        if (action == MotionEvent.ACTION_DOWN) {
            if (handleTouchDown(ev, true)) {
                return true;
            }
        } else if (action == MotionEvent.ACTION_UP || action == MotionEvent.ACTION_CANCEL) {
            if (mTouchCompleteListener != null) {
                mTouchCompleteListener.onTouchComplete();
            }
            mTouchCompleteListener = null;
        }
        clearAllResizeFrames();
        return mDragController.onInterceptTouchEvent(ev);
    }

    @Override
    public boolean onInterceptHoverEvent(MotionEvent ev) {
        if (mLauncher == null || mLauncher.getWorkspace() == null) {
            return false;
        }
        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;
                        }
                        mHoverPointClosesFolder = false;
                        break;
                    case MotionEvent.ACTION_HOVER_MOVE:
                        isOverFolder = isEventOverFolder(currentFolder, ev);
                        if (!isOverFolder && !mHoverPointClosesFolder) {
                            sendTapOutsideFolderAccessibilityEvent(currentFolder.isEditingName());
                            mHoverPointClosesFolder = true;
                            return true;
                        } else if (!isOverFolder) {
                            return true;
                        }
                        mHoverPointClosesFolder = false;
                }
            }
        }
        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 onRequestSendAccessibilityEvent(View child, AccessibilityEvent event) {
        Folder currentFolder = mLauncher.getWorkspace().getOpenFolder();
        if (currentFolder != null) {
            if (child == currentFolder) {
                return super.onRequestSendAccessibilityEvent(child, event);
            }
            // Skip propagating onRequestSendAccessibilityEvent all for other children
            // when a folder is open
            return false;
        }
        return super.onRequestSendAccessibilityEvent(child, event);
    }

    @Override
    public void addChildrenForAccessibility(ArrayList<View> childrenForAccessibility) {
        Folder currentFolder = mLauncher.getWorkspace().getOpenFolder();
        if (currentFolder != null) {
            // Only add the folder as a child for accessibility when it is open
            childrenForAccessibility.add(currentFolder);
        } else {
            super.addChildrenForAccessibility(childrenForAccessibility);
        }
    }

    @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 (mBlockTouches) {
            return true;
        }

        if (action == MotionEvent.ACTION_DOWN) {
            if (handleTouchDown(ev, false)) {
                return true;
            }
        } else if (action == MotionEvent.ACTION_UP || action == MotionEvent.ACTION_CANCEL) {
            if (mTouchCompleteListener != null) {
                mTouchCompleteListener.onTouchComplete();
            }
            mTouchCompleteListener = null;
        }

        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],
                (int) (mTmpXY[0] + scale * descendant.getMeasuredWidth()),
                (int) (mTmpXY[1] + scale * descendant.getMeasuredHeight()));
        return scale;
    }

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

    public float getDescendantCoordRelativeToSelf(View descendant, int[] coord) {
        return getDescendantCoordRelativeToSelf(descendant, coord, false);
    }

    /**
     * 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.
     * @param includeRootScroll Whether or not to account for the scroll of the root descendant:
     *          sometimes this is relevant as in a child's coordinates within the root descendant.
     * @return The factor by which this descendant is scaled relative to this DragLayer. Caution
     *         this scale factor is assumed to be equal in X and Y, and so if at any point this
     *         assumption fails, we will need to return a pair of scale factors.
     */
    public float getDescendantCoordRelativeToSelf(View descendant, int[] coord,
            boolean includeRootScroll) {
        return Utilities.getDescendantCoordRelativeToParent(descendant, this,
                coord, includeRootScroll);
    }

    /**
     * Inverse of {@link #getDescendantCoordRelativeToSelf(View, int[])}.
     */
    public float mapCoordInSelfToDescendent(View descendant, int[] coord) {
        return Utilities.mapCoordInSelfToDescendent(descendant, this, coord);
    }

    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);
    }

    @Override
    public LayoutParams generateLayoutParams(AttributeSet attrs) {
        return new LayoutParams(getContext(), attrs);
    }

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

    // Override to allow type-checking of LayoutParams.
    @Override
    protected boolean checkLayoutParams(ViewGroup.LayoutParams p) {
        return p instanceof LayoutParams;
    }

    @Override
    protected LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) {
        return new LayoutParams(p);
    }

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

        public LayoutParams(Context c, AttributeSet attrs) {
            super(c, attrs);
        }

        public LayoutParams(int width, int height) {
            super(width, height);
        }

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

        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, 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, View anchorView) {
        animateViewIntoPosition(dragView, child, -1, onFinishAnimationRunnable, anchorView);
    }

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

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

        int coord[] = new int[2];
        float childScale = child.getScaleX();
        coord[0] = lp.x + (int) (child.getMeasuredWidth() * (1 - childScale) / 2);
        coord[1] = lp.y + (int) (child.getMeasuredHeight() * (1 - childScale) / 2);

        // 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);
        // We need to account for the scale of the child itself, as the above only accounts for
        // for the scale in parents.
        scale *= childScale;
        int toX = coord[0];
        int toY = coord[1];
        float toScale = scale;
        if (child instanceof TextView) {
            TextView tv = (TextView) child;
            // Account for the source scale of the icon (ie. from AllApps to Workspace, in which
            // the workspace may have smaller icon bounds).
            toScale = scale / dragView.getIntrinsicIconScaleFactor();

            // 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(toScale * tv.getPaddingTop());
            toY -= dragView.getMeasuredHeight() * (1 - toScale) / 2;
            if (dragView.getDragVisualizeOffset() != null) {
                toY -=  Math.round(toScale * dragView.getDragVisualizeOffset().y);
            }

            toX -= (dragView.getMeasuredWidth() - Math.round(scale * child.getMeasuredWidth())) / 2;
        } else if (child instanceof FolderIcon) {
            // Account for holographic blur padding on the drag view
            toY += Math.round(scale * (child.getPaddingTop() - dragView.getDragRegionTop()));
            toY -= scale * Workspace.DRAG_BITMAP_PADDING / 2;
            toY -= (1 - scale) * dragView.getMeasuredHeight() / 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, toScale, toScale,
                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.hypot(to.left - from.left, to.top - from.top);
        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 anchorAdjust = mAnchorView == null ? 0 : (int) (mAnchorView.getScaleX() *
                    (mAnchorViewInitialScrollX - mAnchorView.getScrollX()));

                int xPos = x - mDropView.getScrollX() + anchorAdjust;
                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;
    }

    @Thunk 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) {
        super.onChildViewAdded(parent, child);
        if (mOverlayView != null) {
            // ensure that the overlay view stays on top. we can't use drawing order for this
            // because in API level 16 touch dispatch doesn't respect drawing order.
            mOverlayView.bringToFront();
        }
        updateChildIndices();
    }

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

    @Override
    public void bringChildToFront(View child) {
        super.bringChildToFront(child);
        if (child != mOverlayView && mOverlayView != null) {
            // ensure that the overlay view stays on top. we can't use drawing order for this
            // because in API level 16 touch dispatch doesn't respect drawing order.
            mOverlayView.bringToFront();
        }
        updateChildIndices();
    }

    private void updateChildIndices() {
        mTopViewIndex = -1;
        int childCount = getChildCount();
        for (int i = 0; i < childCount; i++) {
            if (getChildAt(i) instanceof DragView) {
                mTopViewIndex = i;
            }
        }
        mChildCountOnLastUpdate = childCount;
    }

    @Override
    protected int getChildDrawingOrder(int childCount, int i) {
        if (mChildCountOnLastUpdate != childCount) {
            // between platform versions 17 and 18, behavior for onChildViewRemoved / Added changed.
            // Pre-18, the child was not added / removed by the time of those callbacks. We need to
            // force update our representation of things here to avoid crashing on pre-18 devices
            // in certain instances.
            updateChildIndices();
        }

        // i represents the current draw iteration
        if (mTopViewIndex == -1) {
            // in general we do nothing
            return i;
        } else if (i == childCount - 1) {
            // if we have a top index, we return it when drawing last item (highest z-order)
            return mTopViewIndex;
        } else if (i < mTopViewIndex) {
            return i;
        } else {
            // for indexes greater than the top index, we fetch one item above to shift for the
            // displacement of the top index
            return i + 1;
        }
    }

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

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

    void showPageHints() {
        mShowPageHints = true;
        invalidate();
    }

    void hidePageHints() {
        mShowPageHints = false;
        invalidate();
    }

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

    @Override
    protected void dispatchDraw(Canvas canvas) {
        // Draw the background gradient below children.
        if (mBackground != null && mBackgroundAlpha > 0.0f) {
            int alpha = (int) (mBackgroundAlpha * 255);
            mBackground.setAlpha(alpha);
            mBackground.setBounds(0, 0, getMeasuredWidth(), getMeasuredHeight());
            mBackground.draw(canvas);
        }

        super.dispatchDraw(canvas);
    }

    private void drawPageHints(Canvas canvas) {
        if (mShowPageHints) {
            Workspace workspace = mLauncher.getWorkspace();
            int width = getMeasuredWidth();
            Rect childRect = new Rect();
            getDescendantRectRelativeToSelf(workspace.getChildAt(workspace.getChildCount() - 1),
                    childRect);

            int page = workspace.getNextPage();
            final boolean isRtl = isLayoutRtl();
            CellLayout leftPage = (CellLayout) workspace.getChildAt(isRtl ? page + 1 : page - 1);
            CellLayout rightPage = (CellLayout) workspace.getChildAt(isRtl ? page - 1 : page + 1);

            if (leftPage != null && leftPage.isDragTarget()) {
                Drawable left = mInScrollArea && leftPage.getIsDragOverlapping() ?
                        mLeftHoverDrawableActive : mLeftHoverDrawable;
                left.setBounds(0, childRect.top,
                        left.getIntrinsicWidth(), childRect.bottom);
                left.draw(canvas);
            }
            if (rightPage != null && rightPage.isDragTarget()) {
                Drawable right = mInScrollArea && rightPage.getIsDragOverlapping() ?
                        mRightHoverDrawableActive : mRightHoverDrawable;
                right.setBounds(width - right.getIntrinsicWidth(),
                        childRect.top, width, childRect.bottom);
                right.draw(canvas);
            }
        }
    }

    protected boolean drawChild(Canvas canvas, View child, long drawingTime) {
        boolean ret = super.drawChild(canvas, child, drawingTime);

        // We want to draw the page hints above the workspace, but below the drag view.
        if (child instanceof Workspace) {
            drawPageHints(canvas);
        }
        return ret;
    }

    public void setBackgroundAlpha(float alpha) {
        if (alpha != mBackgroundAlpha) {
            mBackgroundAlpha = alpha;
            invalidate();
        }
    }

    public float getBackgroundAlpha() {
        return mBackgroundAlpha;
    }

    public void setTouchCompleteListener(TouchCompleteListener listener) {
        mTouchCompleteListener = listener;
    }

    public interface TouchCompleteListener {
        public void onTouchComplete();
    }
}