Android-->Launcher拖拽事件详解【androidICS4.0--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！


转载请标明出处：http://blog.csdn.net/wdaming1986/article/details/7671318

（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：

[java]
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<STRONG> </STRONG><SPAN style="COLOR: #000000; FONT-SIZE: 16px">// Setup the workspace

mWorkspace.setHapticFeedbackEnabled(false);

mWorkspace.setOnLongClickListener(this);

mWorkspace.setup(dragController);
dragController.addDragListener(mWorkspace);</SPAN>

// 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：

[java]
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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;

}

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：

[java]
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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);

}

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：

[java]
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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();
}

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：

[java]
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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);
}

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：

[java]
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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();

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

[java]
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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() {

}
}

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：

[java]
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/**
* 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;

}

/**
* 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：

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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;

··· ···
}

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。