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通过上一篇文章Android4.0Launcher2源码分析(五)——Workspace的滑动中,已经了解了Launcher的ViewTree中各层所负责的工作,在DragLayer中就负责对快捷图标和AppWidget等组件的拖拽工作。桌面的滑动和图标的拖拽是两项独立的工作,正常情况下我们用手指滑动桌面会触发滑动操作,而当长按一个图标时,则会触发图标的拖拽操作,此时再滑动则会拖拽图标移动而桌面不会滑动。那么这里就分两大部分来探讨:1、拖拽操作的启动。2、拖拽。
一、拖拽操作的启动
那么首先进入Launcher.onCreate()中来探究下如何激活拖拽的状态。
protected void onCreate(Bundle savedInstanceState) { ...... setupViews(); ...... }接着进入setupViews();
private void setupViews() { ...... mWorkspace.setOnLongClickListener(this); ...... }从这里我们可以看到对Workspace设置了OnLongClickListener,而Launcher又实现了这个接口。接着进入Launcher.onLongClick()
public boolean onLongClick(View v) { ...... if (!(v instanceof CellLayout)) { v = (View) v.getParent().getParent(); } resetAddInfo(); CellLayout.CellInfo longClickCellInfo = (CellLayout.CellInfo) v.getTag(); ...... // 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) { ...... } else { if (!(itemUnderLongClick instanceof Folder)) { // User long pressed on an item mWorkspace.startDrag(longClickCellInfo); } } } return true; }当用户在一个item上长按时,则itemUnderLongClick != null,再通过调用Workspace.startDrag()来激活item的拖拽。下面先通过时序图来看下拖拽状态激活所经历的过程:
图标拖拽功能的激活大概可以分为六步,下面就一步一步的探究下其中的实现:
Step1:Workspace.startDrag(CellLayout.CellInfo cellInfo)
void startDrag(CellLayout.CellInfo cellInfo) { View child = cellInfo.cell; ...... mDragInfo = cellInfo; //使图标从桌面上消失,给人一种被“拖到空中”的感觉 child.setVisibility(GONE); ...... 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 //图标的轮廓,在桌面上的对应的位置绘制图标的轮廓,显示当手松开图标时它在桌面上的落点 mDragOutline = createDragOutline(child, canvas, bitmapPadding); beginDragShared(child, this); }在这个方法中,主要的工作就是让图标从桌面上消失,并且显示一个图标的外部轮廓,以表明它将要放置的位置,其显示的效果如下:
显示图标的轮廓可以从视觉上给用户更加好的体验。接着,进入beginDragShared()
Step2:Workspace.beginDragShared(View child,DragSource source)
public void beginDragShared(View child, DragSource source) { ...... // The drag bitmap follows the touch point around on the screen final Bitmap b = createDragBitmap(child, new Canvas(), bitmapPadding); final int bmpWidth = b.getWidth(); //我们将在DragLayer中绘制“拖拽后”的图标,通过DragLayer.getLoactionInDragLayer() //获取在DragLayer中的坐标,并存放在mTempXY中。 mLauncher.getDragLayer().getLocationInDragLayer(child, mTempXY); final int dragLayerX = (int) mTempXY[0] + (child.getWidth() - bmpWidth) / 2; int dragLayerY = mTempXY[1] - bitmapPadding / 2; Point dragVisualizeOffset = null; Rect dragRect = null; //无论child是BubbleTextView或者PagedViewIncon或者FolderIcon的实例 //定位图标的位置与大小 if (child instanceof BubbleTextView || child instanceof PagedViewIcon) { int iconSize = r.getDimensionPixelSize(R.dimen.app_icon_size); int iconPaddingTop = r.getDimensionPixelSize(R.dimen.app_icon_padding_top); int top = child.getPaddingTop(); int left = (bmpWidth - iconSize) / 2; int right = left + iconSize; int bottom = top + iconSize; dragLayerY += top; // Note: The drag region is used to calculate drag layer offsets, but the // dragVisualizeOffset in addition to the dragRect (the size) to position the outline. dragVisualizeOffset = new Point(-bitmapPadding / 2, iconPaddingTop - bitmapPadding / 2); dragRect = new Rect(left, top, right, bottom); } else if (child instanceof FolderIcon) { int previewSize = r.getDimensionPixelSize(R.dimen.folder_preview_size); dragRect = new Rect(0, 0, child.getWidth(), previewSize); } ...... mDragController.startDrag(b, dragLayerX, dragLayerY, source, child.getTag(), DragController.DRAG_ACTION_MOVE, dragVisualizeOffset, dragRect); b.recycle(); }Workspace.beginSharedDrag()中主要所做的工作就是计算拖拽目标位于DragLayer中的坐标和尺寸大小,接着又调用DragController.startDrag()
Step3:DragController.startDrag(Bitmap b ,int dragLayerX, int dragLayerY,DragSource source, Object dragInfo, int dragAction, Point dragOffset, Rect dragRegion)
/** * Starts a drag. * * @param b The bitmap to display as the drag image. It will be re-scaled to the * enlarged size. * @param dragLayerX The x position in the DragLayer of the left-top of the bitmap. * @param dragLayerY The y position in the DragLayer of the left-top of the bitmap. * @param source An object representing where the drag originated * @param dragInfo The data associated with the object that is being dragged * @param dragAction The drag action: either {@link #DRAG_ACTION_MOVE} or * {@link #DRAG_ACTION_COPY} * @param dragRegion Coordinates within the bitmap b for the position of item being dragged. * Makes dragging feel more precise, e.g. you can clip out a transparent border */ public void startDrag(Bitmap b, int dragLayerX, int dragLayerY, DragSource source, Object dragInfo, int dragAction, Point dragOffset, Rect dragRegion) { ...... for (DragListener listener : mListeners) { listener.onDragStart(source, dragInfo, dragAction); } final int registrationX = mMotionDownX - dragLayerX; final int registrationY = mMotionDownY - dragLayerY; final int dragRegionLeft = dragRegion == null ? 0 : dragRegion.left; final int dragRegionTop = dragRegion == null ? 0 : dragRegion.top; //设置mDragging=true,表示拖拽已经开始 //在DragLayer的onInterceptTouchEvent()中根据这个值判断是否拦截MotionEvent mDragging = true; //实例化DragObject,表示拖拽的对象 //封装了拖拽对象的信息 mDragObject = new DropTarget.DragObject(); mDragObject.dragComplete = false; mDragObject.xOffset = mMotionDownX - (dragLayerX + dragRegionLeft); mDragObject.yOffset = mMotionDownY - (dragLayerY + dragRegionTop); mDragObject.dragSource = source; mDragObject.dragInfo = dragInfo; ...... final DragView dragView = mDragObject.dragView = new DragView(mLauncher, b, registrationX, registrationY, 0, 0, b.getWidth(), b.getHeight()); ...... //将拖拽的图标显示在DragLayer中 dragView.show(mMotionDownX, mMotionDownY); handleMoveEvent(mMotionDownX, mMotionDownY); }
代码中显示通过一个for语句调用了DragListener.onDragStart()方法,通知它们已经开始拖拽了,其中由于Workspace实现了DragListener并且添加到了mListeners中。所以Workspace.onDragStart()被调用。然后又封装了一个DragObject对象,封装DragSource、DragInfo和DragView等信息。接着,将调用DragView.show()将DragView显示在DragLayer中。
Step4:DragView.show(int touchX,int touchY)
/** * Create a window containing this view and show it. * * @param touchX the x coordinate the user touched in DragLayer coordinates * @param touchY the y coordinate the user touched in DragLayer coordinates */ public void show(int touchX, int touchY) { //将DragView添加到DragLayer中 mDragLayer.addView(this); //设置位置、尺寸等信息 DragLayer.LayoutParams lp = new DragLayer.LayoutParams(0, 0); lp.width = mBitmap.getWidth(); lp.height = mBitmap.getHeight(); lp.x = touchX - mRegistrationX; lp.y = touchY - mRegistrationY; lp.customPosition = true; setLayoutParams(lp); mLayoutParams = lp; mAnim.start(); }
其中的内容很简单易懂,就是在将DragView添加到了DragLayer中,并且在合适的位置显示了出来。接着应该调用在DragController.startDrag()中调用handleMoveEvent(),这个将在后文将拖拽过程分析时在看。到这一步,拖拽操作的启动过程就完成了。接着就可以拖拽图标了。
二、拖拽
通过了前面文章的分析,已经知道了拖拽过程的实现在DragLayer中,当进行图标的拖拽时,DragLayer.onInterceptTouchEvent()就会对MotionEvent进行拦截。并且
在自身的onTouchEvent()方法中进行操作,从而实现图标的移动。由于onInterceptTouchEvent()拦截了MotionEvent,因此Workspace等UI控件不会接收到事件,从而不会产生
干扰。那么首先进入DragLayer.onInterceptTouchEvent():
public boolean onInterceptTouchEvent(MotionEvent ev) { ...... return mDragController.onInterceptTouchEvent(ev); }代码中省略了与其他功能的不部分代码,最后调用了DragController.onInterceptTouchEvent() ,并取其返回值作为自身方法的返回值。进入DragController.onInterceptTouchEvent()。
/** * Call this from a drag source view. */ public boolean onInterceptTouchEvent(MotionEvent ev) { ...... 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_MOVE: break; case MotionEvent.ACTION_DOWN: // Remember location of down touch mMotionDownX = dragLayerX; mMotionDownY = dragLayerY; mLastDropTarget = null; break; case MotionEvent.ACTION_UP: if (mDragging) { drop(dragLayerX, dragLayerY); } endDrag(); break; case MotionEvent.ACTION_CANCEL: cancelDrag(); break; } return mDragging; }
这里我们关心的是它的返回值。可以看到方法将mDragging作为返回值。当触发了拖拽状态,在的DragController.startDrag()中将mDragging的值改为true。所以这里也将返回true。DragLayer将拦截MotionEvent,并传给自身的onTouchEvent()方法,在onTouchEvent()中对图标进行移动,刷新界面。
/**
* Call this from a drag source view.
*/
public boolean onTouchEvent(MotionEvent ev) {
......
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;
//判断当前的触点是否处于屏幕边缘的ScrollZone,当处于这个区域时
//状态mScrollState将转变为SCROLL,并且在一定时间的停留之后,屏幕滑动到另一屏。
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:
//调用handleMoveEvent()处理图标移动
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) {
//根据目前相对DragLayer的坐标,将图标“降落”到指定的DropTarget上。
drop(dragLayerX, dragLayerY);
}
endDrag();
break;
case MotionEvent.ACTION_CANCEL:
cancelDrag();
break;
}
return true;
}
onTouchEvent()中处理的事件涉及到不同状态之间的转换,以及每种状态之下对相应的MotionEvent的对策。这里同样,从简单的情况入手:图标拖拽起来后,移动一段距离,在屏幕的另一个位置放下。
首先,当拖拽起图标时,拖拽图标的状态被启动,这就是第一部分所探讨的内容。
然后,移动拖拽的图标。此时触发了MotionEvent.ACTION_MOVE事件,紧接着调用handleMoveEvent()来处理移动。进入handleMoveEvent()来看看图标移动是怎么实现的。
private void handleMoveEvent(int x, int y) { //更新在DragLayer中的位置 mDragObject.dragView.move(x, y); // Drop on someone? final int[] coordinates = mCoordinatesTemp; //根据当前的位置寻找DropTarget对象来放置图标 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) { //从最后一次记录的DropTarget中退出 mLastDropTarget.onDragExit(mDragObject); } //进入到当前寻找到的DropTarget dropTarget.onDragEnter(mDragObject); } dropTarget.onDragOver(mDragObject); } else { if (mLastDropTarget != null) { mLastDropTarget.onDragExit(mDragObject); } } mLastDropTarget = dropTarget; // Scroll, maybe, but not if we're in the delete region. boolean inDeleteRegion = false; if (mDeleteRegion != null) { inDeleteRegion = mDeleteRegion.contains(x, y); } // After a scroll, the touch point will still be in the scroll region. // Rather than scrolling immediately, require a bit of twiddling to scroll again final int slop = ViewConfiguration.get(mLauncher).getScaledWindowTouchSlop(); mDistanceSinceScroll += Math.sqrt(Math.pow(mLastTouch[0] - x, 2) + Math.pow(mLastTouch[1] - y, 2)); mLastTouch[0] = x; mLastTouch[1] = y; //判断当前拖拽的图标是否处于ScrollZone即滑动区域。 //并且根据在哪个一个ScrollZone来处理屏幕滑动的方向。 if (!inDeleteRegion && x < mScrollZone) { if (mScrollState == SCROLL_OUTSIDE_ZONE && mDistanceSinceScroll > slop) { mScrollState = SCROLL_WAITING_IN_ZONE; if (mDragScroller.onEnterScrollArea(x, y, SCROLL_LEFT)) { mScrollRunnable.setDirection(SCROLL_LEFT); mHandler.postDelayed(mScrollRunnable, SCROLL_DELAY); } } } else if (!inDeleteRegion && x > mScrollView.getWidth() - mScrollZone) { if (mScrollState == SCROLL_OUTSIDE_ZONE && mDistanceSinceScroll > slop) { mScrollState = SCROLL_WAITING_IN_ZONE; if (mDragScroller.onEnterScrollArea(x, y, SCROLL_RIGHT)) { mScrollRunnable.setDirection(SCROLL_RIGHT); mHandler.postDelayed(mScrollRunnable, SCROLL_DELAY); } } } else { if (mScrollState == SCROLL_WAITING_IN_ZONE) { mScrollState = SCROLL_OUTSIDE_ZONE; mScrollRunnable.setDirection(SCROLL_RIGHT); mHandler.removeCallbacks(mScrollRunnable); mDragScroller.onExitScrollArea(); } } }
handleMoveEvent()主要处理拖拽过程中需要处理的事务。包括:1、在更新图标在屏幕中的位置,并刷新UI。2、判断图标当前所处的位置。包括SCROLL_OUTSIDE_ZONE和SCROLL_WAITING_IN_ZONE,对处于SCROLL_WAITING_IN_ZONE位置时,需要根据具体的位置,向前或向后切换显示的屏幕。再回到上面假设的情况中。则此时只是简单的刷新了位置信息,并重新绘制图标。
最后,当松开拖拽的对象时,触发了MotionEvent.ACTION_UP事件。则进入下面一段代码:
// 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();
先调用handleMoveEvent()确保已经完成了位置移动的操作。接下来调用mHandler.removeCallbacks(mScrollRunnalbe)取消可能存放在消息队列中的滑动任务。接着调用drop(dragLayerX,dragLayerY)将拖拽的对象放置合适的DropTarget对象中(如Workspace,Folder)。
private void drop(float x, float y) { ...... //根据当前的坐标查找适合的DropTarget对象 final DropTarget dropTarget = findDropTarget((int) x, (int) y, coordinates); ...... boolean accepted = false; if (dropTarget != null) { mDragObject.dragComplete = true; dropTarget.onDragExit(mDragObject); if (dropTarget.acceptDrop(mDragObject)) { //将拖拽的对象放置到指定的DropTarget对象中。 dropTarget.onDrop(mDragObject); accepted = true; } } mDragObject.dragSource.onDropCompleted((View) dropTarget, mDragObject, accepted); }
最后调用endDrag()结束拖拽过程。
private void endDrag() { if (mDragging) { //拖拽结束 mDragging = false; for (DragListener listener : mListeners) { //调用回调方法,通知拖拽结束。 listener.onDragEnd(); } if (mDragObject.dragView != null) { //不需要DragView了,将其删除 mDragObject.dragView.remove(); mDragObject.dragView = null; } } }至此,拖拽的图标的过程就结束了。