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。