Android Launcher拖拽事件详解【android4.0--Launcher系列二】

AndroidICS4.0版本的launcher拖 拽的流程，基本和2.3的相似。就是比2.3写的封装的接口多了一些，比如删除类的写法就多了个类。等等。4.0的改变有一些，但是不是特别大。这个月一 直在改动Launcher的缩略图的效果，4.0的缩略图的功能没有实现，还得从2.3的Launcher中摘出来。通过做这个缩略图对Launcher 的模块有一点点了解，拿来分享一下Launcher拖拽的工作流程。有图有真相！

                （1） 先来看看类之间的继承关系

                     

       

                                                          图（1）

                                                                                                                                               

               （2）再来看看Launcher拖拽流程的时序图

               

 

                                                                       图（2）

 

下面咱们分步来解析Launcher拖拽的详细过程：

step 1 ：先来看看Launcher.java这个类的onCreate（）方法中的setupViews（）方法中的一部分代码：

// Setup the workspace
mWorkspace.setHapticFeedbackEnabled(false);
mWorkspace.setOnLongClickListener(this);
mWorkspace.setup(dragController);
dragController.addDragListener(mWorkspace);

 

 

Workspace设置长按事件的监听交给了Launcher.java这个类了。所以在主屏上长按事件会走到Launcher.java----->onLongClick()这个方法中去；

step 2 ：接着我们来看看Launcher.java中onLongClick()的代码：

public boolean onLongClick(View v) {
         ··············
 // The hotseat touch handling does not go through Workspace, and we always allow long press
        // on hotseat items.
        final View itemUnderLongClick = longClickCellInfo.cell;
        boolean allowLongPress = isHotseatLayout(v) || mWorkspace.allowLongPress();
        if (allowLongPress && !mDragController.isDragging()) {
            if (itemUnderLongClick == null) {
                // User long pressed on empty space
                mWorkspace.performHapticFeedback(HapticFeedbackConstants.LONG_PRESS,
                        HapticFeedbackConstants.FLAG_IGNORE_VIEW_SETTING);
                startWallpaper();
            } else {
                if (!(itemUnderLongClick instanceof Folder)) {
                    // User long pressed on an item
                    mWorkspace.startDrag(longClickCellInfo);
                }
            }
        }
        return true;
    }

 

通过itemUnderLongClick == null 来判断，在屏幕上触发长按事件是否选中了shortcut或者widget。如果为空，就启动桌面的壁纸，else，就把拖拽事件往Workspace.java这个类传递。

Step 3 ：通过mWorkspace.startDrag(longClickCellInfo)，把长按事件传递给workspace来处理，具体来看代码：

void startDrag(CellLayout.CellInfo cellInfo) {
     View child = cellInfo.cell;

     // Make sure the drag was started by a long press as opposed to a long click.
     if (!child.isInTouchMode()) {
         return;
     }

     mDragInfo = cellInfo;
     //隐藏拖拽的child
     child.setVisibility(GONE);

     child.clearFocus();
     child.setPressed(false);

     final Canvas canvas = new Canvas();

     // We need to add extra padding to the bitmap to make room for the glow effect
     final int bitmapPadding = HolographicOutlineHelper.MAX_OUTER_BLUR_RADIUS;

     // The outline is used to visualize where the item will land if dropped
     mDragOutline = createDragOutline(child, canvas, bitmapPadding);
     beginDragShared(child, this);
 }

 

上面的代码主要做的工作是：把正在拖拽的这个view隐藏掉，在主屏幕上绘制一个蓝色的，大小和图标相似的一个边框，以表示能在主屏的这个位置放置。

Step 4 ：接着调用beginDragShared(child, this)这个方法，代码如下：

 public void beginDragShared(View child, DragSource source) {
    ··· ···
// Clear the pressed state if necessary
        if (child instanceof BubbleTextView) {
            BubbleTextView icon = (BubbleTextView) child;
            icon.clearPressedOrFocusedBackground();
        }

        mDragController.startDrag(b, dragLayerX, dragLayerY, source, child.getTag(),
                DragController.DRAG_ACTION_MOVE, dragVisualizeOffset, dragRect);
        b.recycle();
    }

 

这个方法做的工作是：开始进行拖拽，绘制正在拖拽的图片，把拖拽的事件交给DragController来处理。

Step 5 ：接 着来看看mDragController.startDrag(b, dragLayerX, dragLayerY, source, child.getTag(), DragController.DRAG_ACTION_MOVE, dragVisualizeOffset, dragRect)这个方法，代码如下：

 public void startDrag(Bitmap b, int dragLayerX, int dragLayerY,
            DragSource source, Object dragInfo, int dragAction, Point dragOffset, Rect dragRegion) {
··· ···
 mDragObject.dragComplete = false;
        mDragObject.xOffset = mMotionDownX - (dragLayerX + dragRegionLeft);
        mDragObject.yOffset = mMotionDownY - (dragLayerY + dragRegionTop);
        mDragObject.dragSource = source;
        mDragObject.dragInfo = dragInfo;
mVibrator.vibrate(VIBRATE_DURATION);

        final DragView dragView = mDragObject.dragView = new DragView(mLauncher, b, registrationX,
                registrationY, 0, 0, b.getWidth(), b.getHeight());

        if (dragOffset != null) {
            dragView.setDragVisualizeOffset(new Point(dragOffset));
        }
        if (dragRegion != null) {
            dragView.setDragRegion(new Rect(dragRegion));
        }

        dragView.show(mMotionDownX, mMotionDownY);
        handleMoveEvent(mMotionDownX, mMotionDownY);
    }

 

这 个方法的作用是：计算要拖拽的view的大小，显示在workspace上，dragView.show(mMotionDownX, mMotionDownY);这个show（）会根据手指的移动而移动的。然后在通过handleMoveEvent（）方法来分发拖拽的目标到底在哪个 目标上。DropTarget一共有3个：workspace，ButtonDropTarget（删除类），Folder；他们分别实现了 DropTarget这个接口。

下面来看看这个接口有一下几个方法：

boolean isDropEnabled();
void onDrop(DragObject dragObject);

    void onDragEnter(DragObject dragObject);

    void onDragOver(DragObject dragObject);

    void onDragExit(DragObject dragObject);
DropTarget getDropTargetDelegate(DragObject dragObject);
boolean acceptDrop(DragObject dragObject);

    // These methods are implemented in Views
    void getHitRect(Rect outRect);
    void getLocationInDragLayer(int[] loc);
    int getLeft();
    int getTop();

 

这些方法不是每个类继承了DropTarget的接口，都要把每个方法都实现，这要看具体的需要来定。

另外这个接口中有个内部类-----DragObject：如下

class DragObject {
        public int x = -1;
        public int y = -1;

        /** X offset from the upper-left corner of the cell to where we touched.  */
        public int xOffset = -1;

        /** Y offset from the upper-left corner of the cell to where we touched.  */
        public int yOffset = -1;

        /** This indicates whether a drag is in final stages, either drop or cancel. It
         * differentiates onDragExit, since this is called when the drag is ending, above
         * the current drag target, or when the drag moves off the current drag object.
         */
        public boolean dragComplete = false;

        /** The view that moves around while you drag.  */
        public DragView dragView = null;

        /** The data associated with the object being dragged */
        public Object dragInfo = null;

        /** Where the drag originated */
        public DragSource dragSource = null;

        /** Post drag animation runnable */
        public Runnable postAnimationRunnable = null;

        /** Indicates that the drag operation was cancelled */
        public boolean cancelled = false;

        public DragObject() {
        }
    }

 

这个类的作用是存储一些坐标，拖拽点距离整个view左上角x轴上的距离，y轴上的距离，还有一些拖拽的信息都保存在这个类中，还有动画线程类等等。在拖拽过程中这些信息都是会用到的。

Step 6 ：接 着来看看handleMoveEvent（）这个类，这个类频繁被调用，因为在DragLayer.java这个类中onTouchEvent（）方法， 最后调用的是 mDragController.onTouchEvent(ev)这个方法，长按后，移动的事件就传递到了DragController中的 onTouchEvent()方法中，先来看看mDragController.onTouchEvent(ev)这个方法，代码如下：

/**
     * Call this from a drag source view.
     */
    public boolean onTouchEvent(MotionEvent ev) {
        if (!mDragging) {
            return false;
        }

        final int action = ev.getAction();
        final int[] dragLayerPos = getClampedDragLayerPos(ev.getX(), ev.getY());
        final int dragLayerX = dragLayerPos[0];
        final int dragLayerY = dragLayerPos[1];

        switch (action) {
        case MotionEvent.ACTION_DOWN:
            // Remember where the motion event started
            mMotionDownX = dragLayerX;
            mMotionDownY = dragLayerY;

            if ((dragLayerX < mScrollZone) || (dragLayerX > mScrollView.getWidth() - mScrollZone)) {
                mScrollState = SCROLL_WAITING_IN_ZONE;
                mHandler.postDelayed(mScrollRunnable, SCROLL_DELAY);
            } else {
                mScrollState = SCROLL_OUTSIDE_ZONE;
            }
            break;
        case MotionEvent.ACTION_MOVE:
            handleMoveEvent(dragLayerX, dragLayerY);
            break;
        case MotionEvent.ACTION_UP:
            // Ensure that we've processed a move event at the current pointer location.
            handleMoveEvent(dragLayerX, dragLayerY);

            mHandler.removeCallbacks(mScrollRunnable);
            if (mDragging) {
                drop(dragLayerX, dragLayerY);
            }
            endDrag();
            break;
        case MotionEvent.ACTION_CANCEL:
            cancelDrag();
            break;
        }

        return true;
    }

 

在这个方法中清楚的可以看见handleMoveEvent（）这个方法会在move，up的时候频繁地调用。

现在再来看看这个handleMoveEvent（）方法，看看它的庐山真面目：

private void handleMoveEvent(int x, int y) {
        mDragObject.dragView.move(x, y);

        // Drop on someone?
        final int[] coordinates = mCoordinatesTemp;
        DropTarget dropTarget = findDropTarget(x, y, coordinates);
        mDragObject.x = coordinates[0];
        mDragObject.y = coordinates[1];
        if (dropTarget != null) {
            DropTarget delegate = dropTarget.getDropTargetDelegate(mDragObject);
            if (delegate != null) {
                dropTarget = delegate;
            }

            if (mLastDropTarget != dropTarget) {
                if (mLastDropTarget != null) {
                    mLastDropTarget.onDragExit(mDragObject);
                }
                dropTarget.onDragEnter(mDragObject);
            }
            dropTarget.onDragOver(mDragObject);
        } else {
            if (mLastDropTarget != null) {
                mLastDropTarget.onDragExit(mDragObject);
            }
        }
        mLastDropTarget = dropTarget;

··· ···
}

   

这 个方法的作用：通过findDropTarget（x, y, coordinates），来判断在哪个拖拽目标里面，然后通过下面的if判断来执行不同的onDragOver，onDragExit等的方法。这样就 在相应的类中去做处理，以后的事情就明朗了。这就是Launcher的拖拽事件的分发与处理，用到了MVC的思想，代码阅读起来还是比较顺利的。有图有真 相。

欢迎大家留言讨论相关问题。