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;