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
java代码：
- at com.android.launcher2.DragController.startDrag
- at com.android.launcher2.Workspace.startDrag
- at com.android.launcher2.Launcher.onLongClick
- at android.view.View.performLongClick
- at android.widget.TextView.performLongClick
- at android.view.View$CheckForLongPress.run
- at android.os.Handler.handleCallback
- at android.os.Handler.dispatchMessage
- at android.os.Looper.loop
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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
java代码：
- 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);
- }
- }
- }
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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
java代码：
- 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);
- }
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