Luancher有一個相對比較復雜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，這篇blog，我將對launcher的拖放功能做深入的了解
1.首先直觀感受什么時候開始拖放？我們長按桌面一個應用圖標或者控件的時候拖放就開始了，包括在all app view中長按應用圖標，下面就是我截取的拖放開始的代碼調用堆棧
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)
桌面應用圖標由Launcher.onLongClick負責監聽處理，插入斷點debug進入onLongclick函數
if (!(v instanceof CellLayout)) {
v = (View) v.getParent();
}
//獲取桌面CellLayout上一個被拖動的對象
CellLayout.CellInfo cellInfo = (CellLayout.CellInfo) v.getTag();
...
if (mWorkspace.allowLongPress()) {
if (cellInfo.cell == null) {
...
} else {
if (!(cellInfo.cell instanceof Folder)) {
...
//調用Workspace.startDrag處理拖動
mWorkspace.startDrag(cellInfo);
}
}
}
我上面只寫出關鍵代碼，首先是獲取被拖動的對象v.getTag()，Tag什么時候被設置進去的了
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);
//判斷區域是否在這個子控件的區間,如果有把child信息賦給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) {
...
//沒有child view 說明沒有點擊桌面圖標項
cellInfo.cell = null;
}
setTag(cellInfo);
}
看了上面代碼知道，當開始點擊桌面時，celllayout就會根據點擊區域去查找在該區域是否有child存在，若有把它設置為tag.cell,沒有,tag.cell設置為null,后面在開始拖放時launcher.onlongclick中對tag進行處理，
這個理順了，再深入到workspace.startDrag函數，workspace.startDrag調用DragController.startDrag去處理拖放
mDragController.startDrag(child, this, child.getTag(), DragController.DRAG_ACTION_MOVE);
再分析一下上面調用的幾個參數
child = tag.cell
this = workspace
child.getTag()是什么呢？在什么時候被設置？再仔細回顧原來launcher加載過程代碼，在launcher.createShortcut中它被設置了：注意下面我代碼中的注釋
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);
//設置favorite(一個桌面Shortcut類型的圖標)的tag
favorite.setTag(info);
favorite.setOnClickListener(this);
return favorite;
}
繼續深入解讀DragController.startDrag函數
public void startDrag(View v, DragSource source, Object dragInfo, int dragAction) {
//設置拖放源view
mOriginator = v;
//獲取view的bitmap
Bitmap b = getViewBitmap(v);
if (b == null) {
// out of memory?
return;
}
//獲取源view在整個屏幕的坐標
int[] loc = mCoordinatesTemp;
v.getLocationOnScreen(loc);
int screenX = loc[0];
int screenY = loc[1];
//該函數功能解讀請繼續往下看
startDrag(b, screenX, screenY, 0, 0, b.getWidth(), b.getHeight(),
source, dragInfo, dragAction);
b.recycle();
//設置原來view不可見
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) {
//隱藏軟鍵盤
if (mInputMethodManager == null) {
mInputMethodManager = (InputMethodManager)
mContext.getSystemService(Context.INPUT_METHOD_SERVICE);
}
mInputMethodManager.hideSoftInputFromWindow(mWindowToken, 0);
//mListener = deletezone,在blog laucher ui框架中有說明該函數，主要就是現實deletezone
if (mListener != null) {
mListener.onDragStart(source, dragInfo, dragAction);
}
//記住手指點擊位置與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);
//創建DragView對象
DragView dragView = mDragView = new DragView(mContext, b, registrationX, registrationY,
textureLeft, textureTop, textureWidth, textureHeight);
//顯示Dragview對象
dragView.show(mWindowToken, (int)mMotionDownX, (int)mMotionDownY);
}
到這里，拖放開始處理的框框基本清楚，但是DragView的創建和顯示還有必要進一步深究
DragView dragView = mDragView = new DragView(mContext, b, registrationX, registrationY,
textureLeft, textureTop, textureWidth, textureHeight);
//函數參數說明：
mContext = launcher
b = 根據拖放源view創建的大小一致的bitmap對象
registrationX = 手指點擊位置與拖放源view 坐標x方向的偏移
registrationY = 手指點擊位置與拖放源view 坐標y方向的偏移
textureLeft = 0
textureTop = 0
textureWidth = b.getWidth()
textureHeight = b.getHeight()
//函數體
super(context);
//獲取window管理器
mWindowManager = WindowManagerImpl.getDefault();
//一個動畫，開始拖放時顯示
mTween = new SymmetricalLinearTween(false, 110 /*ms duration*/, this);
//對源b 做一個縮放產生一個新的bitmap對象
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);
其實函數很簡單，就是記錄一些參數，然后對view圖片做一個縮放處理，並且准備一個tween動畫，在長按桌面圖標后圖標跳躍到手指上顯示該動畫，了解這些，有助於理解函數dragView.show
//windowToken來自與workspace.onattchtowindow時候獲取的view 所有attch的window標識，有這個參數，可以把dragview添加到
workspace所屬的同一個window對象
//touchX,手指點擊在屏幕的位置x
//touchy,手指點擊在屏幕的位置y
public void show(IBinder windowToken, int touchX, int touchY) {
WindowManager.LayoutParams lp;
int pixelFormat;
pixelFormat = PixelFormat.TRANSLUCENT;
//布局參數值的注意的是view位置參數，
//x=touchX-mRegistrationX=touchX-(registrationX + (DRAG_SCALE / 2))=手指點擊位置-view坐標與手指點擊位置偏差加上縮放值
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的父類是Window,也就是說dragview可以拖放到屏幕的任意位置
mWindowManager.addView(this, lp);
mAnimationScale = 1.0f/mScale;
//播放開始拖動動畫(直觀感覺是圖標變大了)
mTween.start(true);
}
2，拖放過程
拖放過程的處理需要深入了解DragController.onTouchEvent(MotionEvent ev)函數的實現，我下面列出關鍵的MotionEvent.ACTION_MOVE部分代碼並作出注釋說明
case MotionEvent.ACTION_MOVE:
// 根據手指坐標移動dragview
mDragView.move((int) ev.getRawX(), (int) ev.getRawY());
// 根據手指所在屏幕坐標獲取目前所在的拖放目的view
final int[] coordinates = mCoordinatesTemp;
DropTarget dropTarget = findDropTarget(screenX, screenY, coordinates);
// 根據不同狀態調用DropTarget的生命周期處理函數
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;
//判斷是否在delete區域
boolean inDeleteRegion = false;
if (mDeleteRegion != null) {
inDeleteRegion = mDeleteRegion.contains(screenX, screenY);
}
//不在delete區域，在左邊切換區
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區，在右邊切換區
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區域
else {
if (mScrollState == SCROLL_WAITING_IN_ZONE) {
mScrollState = SCROLL_OUTSIDE_ZONE;
mScrollRunnable.setDirection(SCROLL_RIGHT);
mHandler.removeCallbacks(mScrollRunnable);
}
}
break;
拖 放過程總的處理思路就是根據當前坐標位置獲取dropTarget的目標位置，然后又根據相關狀態和坐標位置調用dropTarget的對應生命周期函 數，這里面有兩個點需要進一步深入了解，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是一個拖放目標view別表，在laucher初始化等被添加
final ArrayList<DropTarget> dropTargets = mDropTargets;
final int count = dropTargets.size();
//遍歷dropTargets列表，查看{x,y}是否落在dropTarget坐標區域，若是，返回dropTarget。
for (int i=count-1; i>=0; i--) {
final DropTarget target = dropTargets.get(i);
target.getHitRect(r);
//獲取target左上角屏幕坐標
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對象的構造類，通過setDirection設置滾動方向，然后通過一步調用 DragScroller.scrollLeft/scrollRight來對桌面進行向左向右滾動，想深入了解如何實現的，敬請閱讀我相關 blog:Launcher——桌面移動詳解
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.拖放結束，入口還是在DragController.onTouchEvent(MotionEvent ev)
先看調用堆棧：
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關鍵代碼：
case MotionEvent.ACTION_UP:
mHandler.removeCallbacks(mScrollRunnable);
if (mDragging) {
// 拖動過程手指離開屏幕
drop(screenX, screenY);
}
endDrag();
break;
--1.drop(screenX, screenY);
final int[] coordinates = mCoordinatesTemp;
//獲取dropTarget對象
DropTarget dropTarget = findDropTarget((int) x, (int) y, coordinates);
//coordinates=點觸點在dropTarget 中的xy坐標
if (dropTarget != null) {
dropTarget.onDragExit(mDragSource, coordinates[0], coordinates[1],
(int) mTouchOffsetX, (int) mTouchOffsetY, mDragView, mDragInfo);
//根據相關參數判斷是否可dropTarget是否接受該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