android Launcher——拖放功能深入研究

Luancher有一个相对比较复杂的功能就是拖放功能，要深入了解launcher,深入理解拖放功能是有必要的，这篇blog，我将对launcher的拖放功能做深入的了解
1.首先直观感受什么时候开始拖放？我们长按桌面一个应用图标或者控件的时候拖放就开始了，包括在all app view中长按应用图标，下面就是我截取的拖放开始的代码调用堆栈
 at com.android.launcher2.DragController.startDrag(DragController.java:170)
 at com.android.launcher2.Workspace.startDrag(Workspace.java:1068)
 at com.android.launcher2.Launcher.onLongClick(Launcher.java:1683)
 at android.view.View.performLongClick(View.java:2427)
 at android.widget.TextView.performLongClick(TextView.java:7286)
 at android.view.View$CheckForLongPress.run(View.java:8792)
 at android.os.Handler.handleCallback(Handler.java:587)
 at android.os.Handler.dispatchMessage(Handler.java:92)
 at android.os.Looper.loop(Looper.java:123)
 桌面应用图标由Launcher.onLongClick负责监听处理，插入断点debug进入onLongclick函数
         if (!(v instanceof CellLayout)) {
            v = (View) v.getParent();
        }
                                 //获取桌面CellLayout上一个被拖动的对象
         CellLayout.CellInfo cellInfo = (CellLayout.CellInfo) v.getTag();
               ...
        if (mWorkspace.allowLongPress()) {
            if (cellInfo.cell == null) {
                ...
            } else {
                if (!(cellInfo.cell instanceof Folder)) {
                    ...
                    //调用Workspace.startDrag处理拖动
                    mWorkspace.startDrag(cellInfo);
                }
            }
        }
我上面只写出关键代码，首先是获取被拖动的对象v.getTag()，Tag什么时候被设置进去的了
   public boolean onInterceptTouchEvent(MotionEvent ev) {
        ...
        if (action == MotionEvent.ACTION_DOWN) {
                        ...
            boolean found = false;
            for (int i = count - 1; i >= 0; i--) {
                final View child = getChildAt(i);

                if ((child.getVisibility()) == VISIBLE || child.getAnimation() != null) {
                    child.getHitRect(frame);
                    //判断区域是否在这个子控件的区间,如果有把child信息赋给mCellInfo
                    if (frame.contains(x, y)) {
                        final LayoutParams lp = (LayoutParams) child.getLayoutParams();
                        cellInfo.cell = child;
                        cellInfo.cellX = lp.cellX;
                        cellInfo.cellY = lp.cellY;
                        cellInfo.spanX = lp.cellHSpan;
                        cellInfo.spanY = lp.cellVSpan;
                        cellInfo.valid = true;
                        found = true;
                        mDirtyTag = false;
                        break;
                    }
                }
            }
           
            mLastDownOnOccupiedCell = found;

            if (!found) {
                            ...
                            //没有child view 说明没有点击桌面图标项
                cellInfo.cell = null;               
            }
            setTag(cellInfo);
        }
看了上面代码知道，当开始点击桌面时，celllayout就会根据点击区域去查找在该区域是否有child存在，若有把它设置为tag.cell,没有,tag.cell设置为null,后面在开始拖放时launcher.onlongclick中对tag进行处理，
这个理顺了，再深入到workspace.startDrag函数，workspace.startDrag调用DragController.startDrag去处理拖放
mDragController.startDrag(child, this, child.getTag(), DragController.DRAG_ACTION_MOVE);
再分析一下上面调用的几个参数
child = tag.cell
this = workspace
child.getTag()是什么呢？在什么时候被设置？再仔细回顾原来launcher加载过程代码，在launcher.createShortcut中它被设置了：注意下面我代码中的注释
    View createShortcut(int layoutResId, ViewGroup parent, ShortcutInfo info) {
        TextView favorite = (TextView) mInflater.inflate(layoutResId, parent, false);

        favorite.setCompoundDrawablesWithIntrinsicBounds(null,
                new FastBitmapDrawable(info.getIcon(mIconCache)),
                null, null);
        favorite.setText(info.title);
        //设置favorite(一个桌面Shortcut类型的图标)的tag
        favorite.setTag(info);
        favorite.setOnClickListener(this);

        return favorite;
    }
继续深入解读DragController.startDrag函数
    public void startDrag(View v, DragSource source, Object dragInfo, int dragAction) {
            //设置拖放源view
            mOriginator = v;
        //获取view的bitmap
        Bitmap b = getViewBitmap(v);

        if (b == null) {
            // out of memory?
            return;
        }
        //获取源view在整个屏幕的坐标
        int[] loc = mCoordinatesTemp;
        v.getLocationOnScreen(loc);
        int screenX = loc[0];
        int screenY = loc[1];
                                //该函数功能解读请继续往下看
        startDrag(b, screenX, screenY, 0, 0, b.getWidth(), b.getHeight(),
                source, dragInfo, dragAction);

        b.recycle();
        //设置原来view不可见
        if (dragAction == DRAG_ACTION_MOVE) {
            v.setVisibility(View.GONE);
        }
    }

////////////////////////////////////////////////////////////
    public void startDrag(Bitmap b, int screenX, int screenY,
            int textureLeft, int textureTop, int textureWidth, int textureHeight,
            DragSource source, Object dragInfo, int dragAction) {
        //隐藏软键盘
        if (mInputMethodManager == null) {
            mInputMethodManager = (InputMethodManager)
                    mContext.getSystemService(Context.INPUT_METHOD_SERVICE);
        }
        mInputMethodManager.hideSoftInputFromWindow(mWindowToken, 0);
                                //mListener = deletezone,在blog laucher ui框架中有说明该函数，主要就是现实deletezone
        if (mListener != null) {
            mListener.onDragStart(source, dragInfo, dragAction);
        }
                                //记住手指点击位置与屏幕左上角位置偏差
        int registrationX = ((int)mMotionDownX) - screenX;
        int registrationY = ((int)mMotionDownY) - screenY;

        mTouchOffsetX = mMotionDownX - screenX;
        mTouchOffsetY = mMotionDownY - screenY;

        mDragging = true;
        mDragSource = source;
        mDragInfo = dragInfo;

        mVibrator.vibrate(VIBRATE_DURATION);
                                //创建DragView对象
        DragView dragView = mDragView = new DragView(mContext, b, registrationX, registrationY,
                textureLeft, textureTop, textureWidth, textureHeight);
        //显示Dragview对象
        dragView.show(mWindowToken, (int)mMotionDownX, (int)mMotionDownY);
    }
到这里，拖放开始处理的框框基本清楚，但是DragView的创建和显示还有必要进一步深究
        DragView dragView = mDragView = new DragView(mContext, b, registrationX, registrationY,
                textureLeft, textureTop, textureWidth, textureHeight);
//函数参数说明：
mContext = launcher
b = 根据拖放源view创建的大小一致的bitmap对象
registrationX = 手指点击位置与拖放源view 坐标x方向的偏移       
registrationY = 手指点击位置与拖放源view 坐标y方向的偏移       
textureLeft = 0
textureTop = 0
textureWidth = b.getWidth()
textureHeight =  b.getHeight()
//函数体
        super(context);
                                //获取window管理器
        mWindowManager = WindowManagerImpl.getDefault();
        //一个动画，开始拖放时显示
        mTween = new SymmetricalLinearTween(false, 110 /*ms duration*/, this);
                                //对源b 做一个缩放产生一个新的bitmap对象
        Matrix scale = new Matrix();
        float scaleFactor = width;
        scaleFactor = mScale = (scaleFactor + DRAG_SCALE) / scaleFactor;
        scale.setScale(scaleFactor, scaleFactor);

        mBitmap = Bitmap.createBitmap(bitmap, left, top, width, height, scale, true);

        // The point in our scaled bitmap that the touch events are located
        mRegistrationX = registrationX + (DRAG_SCALE / 2);
        mRegistrationY = registrationY + (DRAG_SCALE / 2);
其实函数很简单，就是记录一些参数，然后对view图片做一个缩放处理，并且准备一个tween动画，在长按桌面图标后图标跳跃到手指上显示该动画，了解这些，有助于理解函数dragView.show
//windowToken来自与workspace.onattchtowindow时候获取的view 所有attch的window标识，有这个参数，可以把dragview添加到
workspace所属的同一个window对象
//touchX,手指点击在屏幕的位置x
//touchy,手指点击在屏幕的位置y
    public void show(IBinder windowToken, int touchX, int touchY) {
        WindowManager.LayoutParams lp;
        int pixelFormat;

        pixelFormat = PixelFormat.TRANSLUCENT;
        //布局参数值的注意的是view位置参数，
        //x=touchX-mRegistrationX=touchX-(registrationX + (DRAG_SCALE / 2))=手指点击位置-view坐标与手指点击位置偏差加上缩放值
        lp = new WindowManager.LayoutParams(
                ViewGroup.LayoutParams.WRAP_CONTENT,
                ViewGroup.LayoutParams.WRAP_CONTENT,
                touchX-mRegistrationX, touchY-mRegistrationY,
                WindowManager.LayoutParams.TYPE_APPLICATION_SUB_PANEL,
                WindowManager.LayoutParams.FLAG_LAYOUT_IN_SCREEN
                    | WindowManager.LayoutParams.FLAG_LAYOUT_NO_LIMITS
                    /*| WindowManager.LayoutParams.FLAG_ALT_FOCUSABLE_IM*/,
                pixelFormat);
//        lp.token = mStatusBarView.getWindowToken();
        lp.gravity = Gravity.LEFT | Gravity.TOP;
        lp.token = windowToken;
        lp.setTitle("DragView");
        mLayoutParams = lp;
                                //dragview的父类是Window,也就是说dragview可以拖放到屏幕的任意位置
        mWindowManager.addView(this, lp);

        mAnimationScale = 1.0f/mScale;
        //播放开始拖动动画(直观感觉是图标变大了)
        mTween.start(true);
    }

2，拖放过程
拖放过程的处理需要深入了解DragController.onTouchEvent(MotionEvent ev)函数的实现，我下面列出关键的MotionEvent.ACTION_MOVE部分代码并作出注释说明
                        case MotionEvent.ACTION_MOVE:
                                // 根据手指坐标移动dragview
                                mDragView.move((int) ev.getRawX(), (int) ev.getRawY());

                                // 根据手指所在屏幕坐标获取目前所在的拖放目的view
                                final int[] coordinates = mCoordinatesTemp;
                                DropTarget dropTarget = findDropTarget(screenX, screenY, coordinates);
                                // 根据不同状态调用DropTarget的生命周期处理函数
                                if (dropTarget != null) {
                                        if (mLastDropTarget == dropTarget) {
                                                dropTarget.onDragOver(mDragSource, coordinates[0], coordinates[1], (int) mTouchOffsetX,
                                                                (int) mTouchOffsetY, mDragView, mDragInfo);
                                        } else {
                                                if (mLastDropTarget != null) {
                                                        mLastDropTarget.onDragExit(mDragSource, coordinates[0], coordinates[1],
                                                                        (int) mTouchOffsetX, (int) mTouchOffsetY, mDragView, mDragInfo);
                                                }
                                                dropTarget.onDragEnter(mDragSource, coordinates[0], coordinates[1], (int) mTouchOffsetX,
                                                                (int) mTouchOffsetY, mDragView, mDragInfo);
                                        }
                                } else {
                                        if (mLastDropTarget != null) {
                                                mLastDropTarget.onDragExit(mDragSource, coordinates[0], coordinates[1], (int) mTouchOffsetX,
                                                                (int) mTouchOffsetY, mDragView, mDragInfo);
                                        }
                                }
                                mLastDropTarget = dropTarget;

                                //判断是否在delete区域
                                boolean inDeleteRegion = false;
                                if (mDeleteRegion != null) {
                                        inDeleteRegion = mDeleteRegion.contains(screenX, screenY);
                                }
                                 //不在delete区域，在左边切换区
                                if (!inDeleteRegion && screenX < SCROLL_ZONE) {
                                        if (mScrollState == SCROLL_OUTSIDE_ZONE) {
                                                mScrollState = SCROLL_WAITING_IN_ZONE;
                                                mScrollRunnable.setDirection(SCROLL_LEFT);
                                                mHandler.postDelayed(mScrollRunnable, SCROLL_DELAY);
                                        }
                                }
                                //不在delete区，在右边切换区
                                else if (!inDeleteRegion && screenX > scrollView.getWidth() - SCROLL_ZONE) {
                                        if (mScrollState == SCROLL_OUTSIDE_ZONE) {
                                                mScrollState = SCROLL_WAITING_IN_ZONE;
                                                mScrollRunnable.setDirection(SCROLL_RIGHT);
                                                mHandler.postDelayed(mScrollRunnable, SCROLL_DELAY);
                                        }
                                }
                                //在delete区域
                                else {
                                        if (mScrollState == SCROLL_WAITING_IN_ZONE) {
                                                mScrollState = SCROLL_OUTSIDE_ZONE;
                                                mScrollRunnable.setDirection(SCROLL_RIGHT);
                                                mHandler.removeCallbacks(mScrollRunnable);
                                        }
                                }

                                break;
拖 放过程总的处理思路就是根据当前坐标位置获取dropTarget的目标位置，然后又根据相关状态和坐标位置调用dropTarget的对应生命周期函 数，这里面有两个点需要进一步深入了解，一是查找dropTarget：findDropTarget(screenX, screenY, coordinates)，二是mHandler.postDelayed(mScrollRunnable, SCROLL_DELAY);
--1.findDropTarget
    private DropTarget findDropTarget(int x, int y, int[] dropCoordinates) {
        final Rect r = mRectTemp;
                                //mDropTargets是一个拖放目标view别表，在laucher初始化等被添加
        final ArrayList<DropTarget> dropTargets = mDropTargets;
        final int count = dropTargets.size();
        //遍历dropTargets列表，查看{x,y}是否落在dropTarget坐标区域，若是，返回dropTarget。
        for (int i=count-1; i>=0; i--) {
            final DropTarget target = dropTargets.get(i);
            target.getHitRect(r);
            //获取target左上角屏幕坐标
            target.getLocationOnScreen(dropCoordinates);
            r.offset(dropCoordinates[0] - target.getLeft(), dropCoordinates[1] - target.getTop());
            if (r.contains(x, y)) {
                dropCoordinates[0] = x - dropCoordinates[0];
                dropCoordinates[1] = y - dropCoordinates[1];
                return target;
            }
        }
        return null;
    }
--2.mScrollRunnable
// 看mScrollRunnable对象的构造类，通过setDirection设置滚动方向，然后通过一步调用 DragScroller.scrollLeft/scrollRight来对桌面进行向左向右滚动，想深入了解如何实现的，敬请阅读我相关 blog:Launcher——桌面移动详解
    private class ScrollRunnable implements Runnable {
        private int mDirection;

        ScrollRunnable() {
        }

        public void run() {
            if (mDragScroller != null) {
                if (mDirection == SCROLL_LEFT) {
                    mDragScroller.scrollLeft();
                } else {
                    mDragScroller.scrollRight();
                }
                mScrollState = SCROLL_OUTSIDE_ZONE;
            }
        }

        void setDirection(int direction) {
            mDirection = direction;
        }
    }
3.拖放结束，入口还是在DragController.onTouchEvent(MotionEvent ev)
        先看调用堆栈：
at com.android.launcher2.DragController.endDrag(DragController.java:315)
at com.android.launcher2.DragController.onTouchEvent(DragController.java:471)
at com.android.launcher2.DragLayer.onTouchEvent(DragLayer.java:64)
at android.view.View.dispatchTouchEvent(View.java:3766)
        onTouchEvent关键代码：
                        case MotionEvent.ACTION_UP:
                                mHandler.removeCallbacks(mScrollRunnable);
                                if (mDragging) {
                                        // 拖动过程手指离开屏幕
                                        drop(screenX, screenY);
                                }
                                endDrag();
                                break;
--1.drop(screenX, screenY);
        final int[] coordinates = mCoordinatesTemp;
        //获取dropTarget对象
        DropTarget dropTarget = findDropTarget((int) x, (int) y, coordinates);
        //coordinates=点触点在dropTarget 中的xy坐标

        if (dropTarget != null) {
            dropTarget.onDragExit(mDragSource, coordinates[0], coordinates[1],
                    (int) mTouchOffsetX, (int) mTouchOffsetY, mDragView, mDragInfo);
                    //根据相关参数判断是否可dropTarget是否接受该drag view
            if (dropTarget.acceptDrop(mDragSource, coordinates[0], coordinates[1],
                    (int) mTouchOffsetX, (int) mTouchOffsetY, mDragView, mDragInfo)) {
                dropTarget.onDrop(mDragSource, coordinates[0], coordinates[1],
                        (int) mTouchOffsetX, (int) mTouchOffsetY, mDragView, mDragInfo);
                mDragSource.onDropCompleted((View) dropTarget, true);
                return true;
            } else {
                mDragSource.onDropCompleted((View) dropTarget, false);
                return true;
            }
        }
        return false;

原文：http://blog.csdn.net/stonecao/article/details/6561631