Android Event事件源分析
一、前言：
最近太忙了，因此好久没空来写博客了，差点让大家以为荒废了。。嘻嘻，这不，今天忙里偷个闲，来写这篇文章，帮助自己，也是帮助大家深入了解Event事件流的整个过程，涉及到的文件有：ViewRoot（Impl），ViewGroup，View，PhoneWindow.DecorView及Activity。这些文件，我会抽空将我的理解写到博客。
二、事件流：
2.1 ViewRoot之InputHandler
键盘，触屏，摇杆都会产生事件，那么这些事件，是如何传递处理呢？
首先WMS，即WindowManagerService会：
1. 接收消息；
2. 将消息发送到前端进行处理；
3. 派发消息至ViewRoot； <== 这里，就是我们真正要开始分析地方
那ViewRoot是如何接收的呢？别急，马上就讲。
ViewRoot中，事件接收在InputHandler中完成：
private final InputHandler mInputHandler = new InputHandler() {
public void handleKey(KeyEvent event, InputQueue.FinishedCallback finishedCallback) {
startInputEvent(finishedCallback);
dispatchKey(event, true);
}
public void handleMotion(MotionEvent event, InputQueue.FinishedCallback finishedCallback) {
startInputEvent(finishedCallback);
dispatchMotion(event, true);
}
};
而mInputHandler是在SetView中，去注册完成的：
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
synchronized (this) {
if (mView == null) {
mView = view;
......
if ((mWindowAttributes.inputFeatures
& WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
mInputChannel = new InputChannel();
}
try {
mOrigWindowType = mWindowAttributes.type;
res = sWindowSession.add(mWindow, mSeq, mWindowAttributes,
getHostVisibility(), mAttachInfo.mContentInsets,
mInputChannel);
} catch (RemoteException e) {
mAdded = false;
mView = null;
mAttachInfo.mRootView = null;
mInputChannel = null;
mFallbackEventHandler.setView(null);
unscheduleTraversals();
throw new RuntimeException("Adding window failed", e);
} finally {
if (restore) {
attrs.restore();
}
}
......
if (view instanceof RootViewSurfaceTaker) {
mInputQueueCallback =
((RootViewSurfaceTaker)view).willYouTakeTheInputQueue();
}
if (mInputChannel != null) {
if (mInputQueueCallback != null) {
mInputQueue = new InputQueue(mInputChannel);
mInputQueueCallback.onInputQueueCreated(mInputQueue);
} else {
InputQueue.registerInputChannel(mInputChannel, mInputHandler,
Looper.myQueue());
}
}
......
}
}
}
1. 首先初始化一个Channel，mInputChannel；
2. sWindowSession.add将mInputChannel加入进去；
注：在ViewRoot内部，有一个IWindowSession的静态成员和一个IWindow的非静态成员：
a). IWindowSession负责ViewRoot到WMS的单向请求；
b). IWindow则用于WMS回调ViewRoot；
3. 创建一个输入队列，将Channel和Handler加入（即注册），这样，Event可以通过WMS发送过来。
2.2 ViewRoot之handleMessage
ViewRoot实际上是继承于Handler，它负责UI所有的事件，如刷新、输入事件，焦点等。因此，ViewRoot重载handleMessage，并处理这些事件。
在mInputHandler收到handleKey或dispatchMotion后，都会向handler.sendMessage，我们就看看这两个函数发了什么消息：
键盘按键消息处理，发送一个DISPATCH_KEY消息给handler：
private void dispatchKey(KeyEvent event, boolean sendDone) {
//noinspection ConstantConditions
if (false && event.getAction() == KeyEvent.ACTION_DOWN) {
if (event.getKeyCode() == KeyEvent.KEYCODE_CAMERA) {
if (DBG) Log.d("keydisp", "===================================================");
if (DBG) Log.d("keydisp", "Focused view Hierarchy is:");
debug();
if (DBG) Log.d("keydisp", "===================================================");
}
}
Message msg = obtainMessage(DISPATCH_KEY);
msg.obj = event;
msg.arg1 = sendDone ? 1 : 0;
if (LOCAL_LOGV) Log.v(
TAG, "sending key " + event + " to " + mView);
enqueueInputEvent(msg, event.getEventTime());
}
DISPATCH_POINTER就是TouchEvent，DISPATCH_TRACKBALL是鼠标的滚轮消息，DISPATCH_GENERIC_MOTION是摇杆消息：
private void dispatchMotion(MotionEvent event, boolean sendDone) {
int source = event.getSource();
if ((source & InputDevice.SOURCE_CLASS_POINTER) != 0) {
dispatchPointer(event, sendDone);
} else if ((source & InputDevice.SOURCE_CLASS_TRACKBALL) != 0) {
dispatchTrackball(event, sendDone);
} else {
dispatchGenericMotion(event, sendDone);
}
}
private void dispatchPointer(MotionEvent event, boolean sendDone) {
Message msg = obtainMessage(DISPATCH_POINTER);
msg.obj = event;
msg.arg1 = sendDone ? 1 : 0;
enqueueInputEvent(msg, event.getEventTime());
}
private void dispatchTrackball(MotionEvent event, boolean sendDone) {
Message msg = obtainMessage(DISPATCH_TRACKBALL);
msg.obj = event;
msg.arg1 = sendDone ? 1 : 0;
enqueueInputEvent(msg, event.getEventTime());
}
private void dispatchGenericMotion(MotionEvent event, boolean sendDone) {
Message msg = obtainMessage(DISPATCH_GENERIC_MOTION);
msg.obj = event;
msg.arg1 = sendDone ? 1 : 0;
enqueueInputEvent(msg, event.getEventTime());
}
handleMessage处理很简单，收到后，该调用啥函数就调用啥，不作过多的停留：
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
......
case DISPATCH_KEY:
deliverKeyEvent((KeyEvent)msg.obj, msg.arg1 != 0);
break;
case DISPATCH_POINTER:
deliverPointerEvent((MotionEvent) msg.obj, msg.arg1 != 0);
break;
case DISPATCH_TRACKBALL:
deliverTrackballEvent((MotionEvent) msg.obj, msg.arg1 != 0);
break;
case DISPATCH_GENERIC_MOTION:
deliverGenericMotionEvent((MotionEvent) msg.obj, msg.arg1 != 0);
break;
......
}
}
这几个消息处理都大同小异，因此，本篇以DISPATCH_POINTER（即TouchEvent）为代表吧。
2.3 消息传递及分发：
2.3.1 deliverPointerEvent
private void deliverPointerEvent(MotionEvent event, boolean sendDone) {
if (ViewDebug.DEBUG_LATENCY) {
mInputEventDeliverTimeNanos = System.nanoTime();
}
final boolean isTouchEvent = event.isTouchEvent();
if (mInputEventConsistencyVerifier != null) {
if (isTouchEvent) {
mInputEventConsistencyVerifier.onTouchEvent(event, 0);
} else {
mInputEventConsistencyVerifier.onGenericMotionEvent(event, 0);
}
}
// If there is no view, then the event will not be handled.
if (mView == null || !mAdded) {
finishMotionEvent(event, sendDone, false);
return;
}
// Translate the pointer event for compatibility, if needed.
if (mTranslator != null) {
mTranslator.translateEventInScreenToAppWindow(event);
}
// Enter touch mode on down or scroll.
final int action = event.getAction();
if (action == MotionEvent.ACTION_DOWN || action == MotionEvent.ACTION_SCROLL) {
ensureTouchMode(true);
}
// Offset the scroll position.
if (mCurScrollY != 0) {
event.offsetLocation(0, mCurScrollY);
}
if (MEASURE_LATENCY) {
lt.sample("A Dispatching PointerEvents", System.nanoTime() - event.getEventTimeNano());
}
// Remember the touch position for possible drag-initiation.
if (isTouchEvent) {
mLastTouchPoint.x = event.getRawX();
mLastTouchPoint.y = event.getRawY();
}
// Dispatch touch to view hierarchy.
boolean handled = mView.dispatchPointerEvent(event);
if (MEASURE_LATENCY) {
lt.sample("B Dispatched PointerEvents ", System.nanoTime() - event.getEventTimeNano());
}
if (handled) {
finishMotionEvent(event, sendDone, true);
return;
}
// Pointer event was unhandled.
finishMotionEvent(event, sendDone, false);
}
这里面看似一大堆，实际上，正常的会走到这条语句：
boolean handled = mView.dispatchPointerEvent(event);
看到这里，大家还是会纳闷，我平常看到的都是dispatchTouchEvent，别急嘛，接下来就会明朗。
如果mView.dispatchPointerEvent(event)返回是false，表明没有控件需要，因此，最终将走到finishMotionEvent，同样，返回true也是走到这函数，这函数是啥意思呢？大家不需深入关心，只不过是将这次的消息结果告诉Window而已。
2.3.2 dispatchPointerEvent （View.java）
public final boolean dispatchPointerEvent(MotionEvent event) {
if (event.isTouchEvent()) {
return dispatchTouchEvent(event);
} else {
return dispatchGenericMotionEvent(event);
}
}
我们常看到的dispatchTouchEvent出现了。
大家注意下，这个方法是final，而我们知道，ViewGroup是继承View的，因此，ViewGroup或但凡继承View的，都不能Override（重写）该方法，但可以继承该方法。
在ViewRoot中，mView其实就是PhoneWindow.DecorView，而decorView是继承于FrameLayout，FrameLayout继承于ViewGroup，因此，dispatchTouchEvent也就会走到PhoneWindow.DecorView（也重写，并调用super.dispatchTouchEvent）走到ViewGroup中。在ViewGroup中，有重写dispatchTouchEvent方法。
2.3.3 dispatchTouchEvent（ViewGroup.java）
这个方法是本篇中的重中之重，大家可看好啦。
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(ev, 1);
}
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Throw away all previous state when starting a new touch gesture.
// The framework may have dropped the up or cancel event for the previous gesture
// due to an app switch, ANR, or some other state change.
cancelAndClearTouchTargets(ev);
resetTouchState();
}
// Check for interception.
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);
ev.setAction(action); // restore action in case it was changed
} else {
intercepted = false;
}
} else {
// There are no touch targets and this action is not an initial down
// so this view group continues to intercept touches.
intercepted = true;
}
// Check for cancelation.
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
// Update list of touch targets for pointer down, if needed.
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
TouchTarget newTouchTarget = null;
boolean alreadyDispatchedToNewTouchTarget = false;
if (!canceled && !intercepted) {
if (actionMasked == MotionEvent.ACTION_DOWN
|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
final int actionIndex = ev.getActionIndex(); // always 0 for down
final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex)
: TouchTarget.ALL_POINTER_IDS;
// Clean up earlier touch targets for this pointer id in case they
// have become out of sync.
removePointersFromTouchTargets(idBitsToAssign);
final int childrenCount = mChildrenCount;
if (childrenCount != 0) {
// Find a child that can receive the event.
// Scan children from front to back.
final View[] children = mChildren;
final float x = ev.getX(actionIndex);
final float y = ev.getY(actionIndex);
for (int i = childrenCount - 1; i >= 0; i--) {
final View child = children[i];
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
continue;
}
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
// Child is already receiving touch within its bounds.
// Give it the new pointer in addition to the ones it is handling.
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
resetCancelNextUpFlag(child);
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// Child wants to receive touch within its bounds.
mLastTouchDownTime = ev.getDownTime();
mLastTouchDownIndex = i;
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
}
}
if (newTouchTarget == null && mFirstTouchTarget != null) {
// Did not find a child to receive the event.
// Assign the pointer to the least recently added target.
newTouchTarget = mFirstTouchTarget;
while (newTouchTarget.next != null) {
newTouchTarget = newTouchTarget.next;
}
newTouchTarget.pointerIdBits |= idBitsToAssign;
}
}
}
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
// Dispatch to touch targets, excluding the new touch target if we already
// dispatched to it. Cancel touch targets if necessary.
TouchTarget predecessor = null;
TouchTarget target = mFirstTouchTarget;
while (target != null) {
final TouchTarget next = target.next;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
handled = true;
}
if (cancelChild) {
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
predecessor.next = next;
}
target.recycle();
target = next;
continue;
}
}
predecessor = target;
target = next;
}
}
// Update list of touch targets for pointer up or cancel, if needed.
if (canceled
|| actionMasked == MotionEvent.ACTION_UP
|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {
resetTouchState();
} else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) {
final int actionIndex = ev.getActionIndex();
final int idBitsToRemove = 1 << ev.getPointerId(actionIndex);
removePointersFromTouchTargets(idBitsToRemove);
}
}
if (!handled && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1);
}
return handled;
}
一上来，就遇到个onFilterTouchEventForSecurity方法，接下来，所有的代码，都包函数在其里面，只有它返回true，才会继续执行下去。
public boolean onFilterTouchEventForSecurity(MotionEvent event) {
//noinspection RedundantIfStatement
if ((mViewFlags & FILTER_TOUCHES_WHEN_OBSCURED) != 0
&& (event.getFlags() & MotionEvent.FLAG_WINDOW_IS_OBSCURED) != 0) {
// Window is obscured, drop this touch.
return false;
}
return true;
}
默让是返回true的，这个方法可以继承，可以自己加一些安全策略来决定是否响应TouchEvent，咱们只需知道有这么个方法，可以在以后开发应用中，有需要时，记着有这么个它可以拦截就行。
// Handle an initial down.
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Throw away all previous state when starting a new touch gesture.
// The framework may have dropped the up or cancel event for the previous gesture
// due to an app switch, ANR, or some other state change.
cancelAndClearTouchTargets(ev);
resetTouchState();
}
/**
* Cancels and clears all touch targets.
*/
private void cancelAndClearTouchTargets(MotionEvent event) {
if (mFirstTouchTarget != null) {
boolean syntheticEvent = false;
if (event == null) {
final long now = SystemClock.uptimeMillis();
event = MotionEvent.obtain(now, now,
MotionEvent.ACTION_CANCEL, 0.0f, 0.0f, 0);
event.setSource(InputDevice.SOURCE_TOUCHSCREEN);
syntheticEvent = true;
}
for (TouchTarget target = mFirstTouchTarget; target != null; target = target.next) {
resetCancelNextUpFlag(target.child);
dispatchTransformedTouchEvent(event, true, target.child, target.pointerIdBits);
}
clearTouchTargets();
if (syntheticEvent) {
event.recycle();
}
}
}
如果是DOWN事件，则将之前的Targets和状态都清除，因为上次的应用在运行过程中有可能ANR等导致目前的状态紊乱。
我们可以看到，在cancelAndClearTouchTargets中，会对上一次保存在TouchTarget中的Child都发送ACTION_CANCEL事件，然后将TouchTarget中的Child全部清除。
| Child收到TOUCH ACTION后，开始做自己的事，这时，还用户手未松开，即还是一直是ACTION_MOVE，突然，用户的手一不小心移动到该Child边界外，那么这时，Child是永远不会收到ACTION_UP事件了，那么，Child的状态有可能会乱掉（做滚动视图时，会根据MOVE距离来scrollTo / scrollBy View，然而用户手指移动出界，那么，本该是UP时将View复位或是自动滚动到该停止的地方却没有，界面就乱了。因此，Google Android官方解释为：此时的CANCEL 等同于 UP）。 |
// Check for interception.
final boolean intercepted;
if (actionMasked == MotionEvent.ACTION_DOWN
|| mFirstTouchTarget != null) {
final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (!disallowIntercept) {
intercepted = onInterceptTouchEvent(ev);
ev.setAction(action); // restore action in case it was changed
} else {
intercepted = false;
}
} else {
// There are no touch targets and this action is not an initial down
// so this view group continues to intercept touches.
intercepted = true;
}
这个地方，很重要，为啥？通常，我们在开发时，如果需要根据不同的手势方向，来做不同的效果，如：应用首页支持左、右滑动页，以及首页正文是ListView时，就需要去重写onInterceptTouchEvent(ev)方法（只有ViewGroup才有此方法，View没有）：
如果返回false，本次TouchEvent可以继续往下传递给Child（View / ViewGroup）；
如果返回true，则本次及之后的TouchEvent都不会往下传递，而会将消息发送给当前ViewGroup的onTouchEvent中。
系统默认该方法返回false。
if条件判断actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null 只要两者满足其一就行，那么，怎么样才走到else？后续ACTION不为DOWN（即ACTION_MOVE, ACTION_UP, ACTION_CANCEL）且TouchTarget列表为空（函数开始时若是DOWN就清除），就表明当前ViewGroup已经在之前的onInterceptTouchEvent中返回了true，即“我要拦截”。
|
1. 此时ACTION_DOWN，但 TouchTarget列表为空，走if, 且调用当前ViewGroup.onInterceptTouchEvent，如果是true，后续ACTION就走else，下面的代码添加，查找TouchTarget就不会走到，反之，会去找ViewGroup的Child，看看坐标落在谁身上，并添加至TouchTarget中； 2. 若第1步中，返回的是false，那么，此时ACTION_MOVE（正常情况下，点击不算），虽然此时不为ACTION_DOWN，但TouchTarget不为空，所以仍走if, 且调用ViewGroup.onInterceptTouchEvent，此时返回true，那么在之后会将mFirstTouchTarget列表设为NULL，之后的ACTION不会再走if. |
// Check for cancelation.
final boolean canceled = resetCancelNextUpFlag(this)
|| actionMasked == MotionEvent.ACTION_CANCEL;
检查当前是否被设置CANCEL标志，或者当前消息是ACTION_CANCEL
final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0;
这句话的意思是：是否将当前的Event发送给多个Child View（多个Child View可能重叠，因此Pointer是否都给他们），默认是true，即重叠区域的Child View都可以接收。
如果没有Cancel，也没有设置拦截，则继续往下运行：
final int childrenCount = mChildrenCount;
if (childrenCount != 0) {
// Find a child that can receive the event.
// Scan children from front to back.
final View[] children = mChildren;
final float x = ev.getX(actionIndex);
final float y = ev.getY(actionIndex);
for (int i = childrenCount - 1; i >= 0; i--) {
final View child = children[i];
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
continue;
}
......
}
}
默认final int actionIndex = ev.getActionIndex(); // always 0 for down，然后，开始从最后添加的Child View开始往前遍历，当前ChildView是否可见或当前正在动画，且触摸点[x，y]是否落在ChildView区域中：
/**
* Returns true if a child view can receive pointer events.
* @hide
*/
private static boolean canViewReceivePointerEvents(View child) {
return (child.mViewFlags & VISIBILITY_MASK) == VISIBLE
|| child.getAnimation() != null;
}
/**
* Returns true if a child view contains the specified point when transformed
* into its coordinate space.
* Child must not be null.
* @hide
*/
protected boolean isTransformedTouchPointInView(float x, float y, View child,
PointF outLocalPoint) {
float localX = x + mScrollX - child.mLeft;
float localY = y + mScrollY - child.mTop;
if (! child.hasIdentityMatrix() && mAttachInfo != null) {
final float[] localXY = mAttachInfo.mTmpTransformLocation;
localXY[0] = localX;
localXY[1] = localY;
child.getInverseMatrix().mapPoints(localXY);
localX = localXY[0];
localY = localXY[1];
}
final boolean isInView = child.pointInView(localX, localY);
if (isInView && outLocalPoint != null) {
outLocalPoint.set(localX, localY);
}
return isInView;
}
首先，计算坐标（可能存在滚动条的滚动后的结果），然后判断坐标点是否落在Child中，并返回（true表明点落在Child中）；
newTouchTarget = getTouchTarget(child);
if (newTouchTarget != null) {
// Child is already receiving touch within its bounds.
// Give it the new pointer in addition to the ones it is handling.
newTouchTarget.pointerIdBits |= idBitsToAssign;
break;
}
查找TouchTarget列表，如果能找到，将它与当前的pointerId联系起来（pointerId最多有0 ~ 31个，因此用int来表示位图），如果没找到，则接下来，将该Child加到到TouchTarget列表中：
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// Child wants to receive touch within its bounds.
mLastTouchDownTime = ev.getDownTime();
mLastTouchDownIndex = i;
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true;
break;
}
如果CANCEL，或onInterceptTouchEvent，则直接跳过以上，那么，亲爱的朋友，如果你看的快，应该还没过30秒吧，上面这段代码，到底做了啥？没看懂？OH~MY GOD！好吧，我总结归纳上面的代码：
如果没有CANCEL且拦截，则我们需要从当前ViewGroup众多的Child中，从最后往前找到一个刚好符合即Visible，坐标点又落上该Child区域的，并将它与pointerId关联起来。（为啥从后往前找？ -_-||| 因为，AddView 或 AddChildView总是将当前添加的VIEW显示在最前面，你点击它，当然是想让你看到的VIEW对你产生“物理”反应啦！）。
继续，手有点累，头有点晕，眼有点花，但无法阻碍我的热情。（我的热情，好像一把火！）
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
handled = dispatchTransformedTouchEvent(ev, canceled, null,
TouchTarget.ALL_POINTER_IDS);
} else {
// Dispatch to touch targets, excluding the new touch target if we already
// dispatched to it. Cancel touch targets if necessary.
TouchTarget predecessor = null;
TouchTarget target = mFirstTouchTarget;
while (target != null) {
final TouchTarget next = target.next;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
if (dispatchTransformedTouchEvent(ev, cancelChild,
target.child, target.pointerIdBits)) {
handled = true;
}
if (cancelChild) {
if (predecessor == null) {
mFirstTouchTarget = next;
} else {
predecessor.next = next;
}
target.recycle();
target = next;
continue;
}
}
predecessor = target;
target = next;
}
}
if 就是当 intercept 后执行的，同样会执行到dispatchTransformedTouchEvent，先看else部分，顺带分析 if 情况；
这里有个while循环遍历整个TouchTarget，如果是新添加的target，则表明已经handle过了。咦，哪里处理过？在上面代码，如果没有CANCEL && 拦截时，有这么一句：
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)){...}
这里的while遍历，也会调用这个函数，这个也基本上是dispatchTouchEvent中最后一个重要的方法了，因为，之后就是对UP做一些重置状态的动作，并返回handled（是否有ChildView响应此次TouchEvent）。
2.3.4 dispatchTransformedTouchEvent （ViewGroup.java）
/**
* Transforms a motion event into the coordinate space of a particular child view,
* filters out irrelevant pointer ids, and overrides its action if necessary.
* If child is null, assumes the MotionEvent will be sent to this ViewGroup instead.
*/
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;
// Canceling motions is a special case. We don't need to perform any transformations
// or filtering. The important part is the action, not the contents.
final int oldAction = event.getAction();
if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
event.setAction(MotionEvent.ACTION_CANCEL);
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
handled = child.dispatchTouchEvent(event);
}
event.setAction(oldAction);
return handled;
}
// Calculate the number of pointers to deliver.
final int oldPointerIdBits = event.getPointerIdBits();
final int newPointerIdBits = oldPointerIdBits & desiredPointerIdBits;
// If for some reason we ended up in an inconsistent state where it looks like we
// might produce a motion event with no pointers in it, then drop the event.
if (newPointerIdBits == 0) {
return false;
}
// If the number of pointers is the same and we don't need to perform any fancy
// irreversible transformations, then we can reuse the motion event for this
// dispatch as long as we are careful to revert any changes we make.
// Otherwise we need to make a copy.
final MotionEvent transformedEvent;
if (newPointerIdBits == oldPointerIdBits) {
if (child == null || child.hasIdentityMatrix()) {
if (child == null) {
handled = super.dispatchTouchEvent(event);
} else {
final float offsetX = mScrollX - child.mLeft;
final float offsetY = mScrollY - child.mTop;
event.offsetLocation(offsetX, offsetY);
handled = child.dispatchTouchEvent(event);
event.offsetLocation(-offsetX, -offsetY);
}
return handled;
}
transformedEvent = MotionEvent.obtain(event);
} else {
transformedEvent = event.split(newPointerIdBits);
}
// Perform any necessary transformations and dispatch.
if (child == null) {
handled = super.dispatchTouchEvent(transformedEvent);
} else {
final float offsetX = mScrollX - child.mLeft;
final float offsetY = mScrollY - child.mTop;
transformedEvent.offsetLocation(offsetX, offsetY);
if (! child.hasIdentityMatrix()) {
transformedEvent.transform(child.getInverseMatrix());
}
handled = child.dispatchTouchEvent(transformedEvent);
}
// Done.
transformedEvent.recycle();
return handled;
}
看下来，这方法没啥好讲的，如果CANCEL了，Child为空就super.dispatchTouchEvent，否则就child.dispatchTouchEvent；同样，后面的正常流程也是super/child dispatchTouchEvent。
child如果是ViewGroup，那么继续重复以上过程，如果是view，那么就走View.dispatchTouchEvent。如果child == NULL，则ViewGroup.super.dispatchTouchEvent实际上也是走View.dispatchTouchEvent。
2.3.5 View.dispatchTouchEvent
/**
* Pass the touch screen motion event down to the target view, or this
* view if it is the target.
*
* @param event The motion event to be dispatched.
* @return True if the event was handled by the view, false otherwise.
*/
public boolean dispatchTouchEvent(MotionEvent event) {
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(event, 0);
}
if (onFilterTouchEventForSecurity(event)) {
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
return true;
}
if (onTouchEvent(event)) {
return true;
}
}
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
return false;
}
如果有注册 OnTouchListener，那么就先将该event 给这个监听，如果该Listener回为true，那么此次event 就算完成；否则，调用View.onTouchEvent，如果是ViewGroup的Child，那就是Child.onTouchEvent，如果之前 intercept ，那么就是当前 ViewGroup 自己的 onTouchEvent。如果最终都没有VIEW处理此次EVENT，则最终返回给ViewRoot，将会丢掉此EVENT。
至此，整个Event 流程就走了一遍，我想大家也都清楚了吧，若文中写的不对的地方，也请大家指出，欢迎一起讨论！谢谢。