Android11 事件分发流程

在Android 11 输入系统之InputDispatcher和应用窗口建立联系一文中介绍到，当InputDispatcher写入数据后，客户端这边就会调用handleEvent方法接收数据

//frameworks\base\core\jni\android_view_InputEventReceiver.cpp
int NativeInputEventReceiver::handleEvent(int receiveFd, int events, void* data) {//省略if (events & ALOOPER_EVENT_INPUT) {//之前构造数据的时候，events为ALOOPER_EVENT_INPUTJNIEnv* env = AndroidRuntime::getJNIEnv();status_t status = consumeEvents(env, false /*consumeBatches*/, -1, nullptr);mMessageQueue->raiseAndClearException(env, "handleReceiveCallback");return status == OK || status == NO_MEMORY ? 1 : 0;}//省略

继续调用consumeEvents处理

//frameworks\base\core\jni\android_view_InputEventReceiver.cpp
status_t NativeInputEventReceiver::consumeEvents(JNIEnv* env,bool consumeBatches, nsecs_t frameTime, bool* outConsumedBatch) {//省略for (;;) {uint32_t seq;InputEvent* inputEvent;status_t status = mInputConsumer.consume(&mInputEventFactory,consumeBatches, frameTime, &seq, &inputEvent);//1//省略case AINPUT_EVENT_TYPE_MOTION: {MotionEvent* motionEvent = static_cast<MotionEvent*>(inputEvent);//使用inputEvent构造MotionEvent对象if ((motionEvent->getAction() & AMOTION_EVENT_ACTION_MOVE) && outConsumedBatch) {*outConsumedBatch = true;}inputEventObj = android_view_MotionEvent_obtainAsCopy(env, motionEvent);//创建java层的MotionEvent对象，并将该对象的mNativePtr指向c++的MotionEvent对象break;}//省略env->CallVoidMethod(receiverObj.get(),gInputEventReceiverClassInfo.dispatchInputEvent, seq, inputEventObj);//2//省略
}

注释1处接收InputDispatcher发过来的数据，并将数据封装成InputEvent对象，注释2处通过JNI调用InputEventReceiver的dispatchInputEvent方法
先来看一下如何接收数据的

//frameworks\native\libs\input\InputTransport.cpp
status_t InputConsumer::consume(InputEventFactoryInterface* factory, bool consumeBatches,nsecs_t frameTime, uint32_t* outSeq, InputEvent** outEvent) {//省略while (!*outEvent) {if (mMsgDeferred) {// mMsg contains a valid input message from the previous call to consume// that has not yet been processed.mMsgDeferred = false;} else {// Receive a fresh message.status_t result = mChannel->receiveMessage(&mMsg);//1//省略switch (mMsg.header.type) {case InputMessage::Type::MOTION: {//省略MotionEvent* motionEvent = factory->createMotionEvent();if (!motionEvent) return NO_MEMORY;updateTouchState(mMsg);initializeMotionEvent(motionEvent, &mMsg);//2*outSeq = mMsg.body.motion.seq;*outEvent = motionEvent;//省略break;}}

注释1处接收数据，接收到的数据是InputMessage对象。注释2处根据读取到的InputMessage，创建motionEvent对象

//frameworks\native\libs\input\InputTransport.cpp
status_t InputChannel::receiveMessage(InputMessage* msg) {ssize_t nRead;do {nRead = ::recv(mFd.get(), msg, sizeof(InputMessage), MSG_DONTWAIT);//读fd} while (nRead == -1 && errno == EINTR);

consume方法得到数据并将数据封装成motionEvent对象后，回到consumeEvents方法，继续调用InputEventReceiver的dispatchInputEvent方法

//frameworks\base\core\java\android\view\InputEventReceiver.java
private void dispatchInputEvent(int seq, InputEvent event) {mSeqMap.put(event.getSequenceNumber(), seq);onInputEvent(event);
}

调用onInputEvent方法，WindowInputEventReceiver继承InputEventReceiver，调用WindowInputEventReceiver的onInputEvent方法

//frameworks\base\core\java\android\view\ViewRootImpl.java
final class WindowInputEventReceiver extends InputEventReceiver {public WindowInputEventReceiver(InputChannel inputChannel, Looper looper) {super(inputChannel, looper);}@Overridepublic void onInputEvent(InputEvent event) {Trace.traceBegin(Trace.TRACE_TAG_VIEW, "processInputEventForCompatibility");//省略if (processedEvents != null) {//省略} else {enqueueInputEvent(event, this, 0, true);//注意第二个参数传入的是当前对象}}

enqueueInputEvent

//frameworks\base\core\java\android\view\ViewRootImpl.java
void enqueueInputEvent(InputEvent event,InputEventReceiver receiver, int flags, boolean processImmediately) {QueuedInputEvent q = obtainQueuedInputEvent(event, receiver, flags);//省略if (processImmediately) {//processImmediately传进来的是truedoProcessInputEvents();} else {scheduleProcessInputEvents();}}

doProcessInputEvents

//frameworks\base\core\java\android\view\ViewRootImpl.java
void doProcessInputEvents() {// Deliver all pending input events in the queue.while (mPendingInputEventHead != null) {//省略deliverInputEvent(q);}//省略}

deliverInputEvent

//frameworks\base\core\java\android\view\ViewRootImpl.java
private void deliverInputEvent(QueuedInputEvent q) {//省略try {//省略InputStage stage;if (q.shouldSendToSynthesizer()) {stage = mSyntheticInputStage;} else {stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;//1}//省略if (stage != null) {handleWindowFocusChanged();stage.deliver(q);//2} else {finishInputEvent(q);}} finally {Trace.traceEnd(Trace.TRACE_TAG_VIEW);}}

注释1处设置InputStage，对于触摸事件，默认是忽略输入法的，所以stage 为mFirstPostImeInputStage 对象。注释2处 调用mFirstPostImeInputStage 的deliver方法。
系统中有多个InputStage组成的一个链表，在setView方法中设置的

//frameworks\base\core\java\android\view\ViewRootImpl.java
// Set up the input pipeline.
CharSequence counterSuffix = attrs.getTitle();
mSyntheticInputStage = new SyntheticInputStage();
InputStage viewPostImeStage = new ViewPostImeInputStage(mSyntheticInputStage);
InputStage nativePostImeStage = new NativePostImeInputStage(viewPostImeStage,"aq:native-post-ime:" + counterSuffix);
InputStage earlyPostImeStage = new EarlyPostImeInputStage(nativePostImeStage);
InputStage imeStage = new ImeInputStage(earlyPostImeStage,"aq:ime:" + counterSuffix);
InputStage viewPreImeStage = new ViewPreImeInputStage(imeStage);
InputStage nativePreImeStage = new NativePreImeInputStage(viewPreImeStage,"aq:native-pre-ime:" + counterSuffix);

deliver方法的原理就是输入事件会经过这些InputStage依次处理（调用onProcess方法），如果事件已经被上一个消费处理了，后面的stage就不会处理了。触摸事件会传递到ViewPostImeInputStage中处理

//frameworks\base\core\java\android\view\ViewRootImpl.java
final class ViewPostImeInputStage extends InputStage {public ViewPostImeInputStage(InputStage next) {super(next);}@Overrideprotected int onProcess(QueuedInputEvent q) {if (q.mEvent instanceof KeyEvent) {return processKeyEvent(q);} else {final int source = q.mEvent.getSource();if ((source & InputDevice.SOURCE_CLASS_POINTER) != 0) {return processPointerEvent(q);} else if ((source & InputDevice.SOURCE_CLASS_TRACKBALL) != 0) {return processTrackballEvent(q);} else {return processGenericMotionEvent(q);}}}

对于触摸事件，调用processPointerEvent继续处理

//frameworks\base\core\java\android\view\ViewRootImpl.java
private int processPointerEvent(QueuedInputEvent q) {final MotionEvent event = (MotionEvent)q.mEvent;mAttachInfo.mUnbufferedDispatchRequested = false;mAttachInfo.mHandlingPointerEvent = true;boolean handled = mView.dispatchPointerEvent(event);//1//省略return handled ? FINISH_HANDLED : FORWARD;
}

主要是调用mView的dispatchPointerEvent方法，这里的mView是DecorView,DecorView中没有实现该方法，在其父类View中实现

//frameworks\base\core\java\android\view\View.java
@UnsupportedAppUsagepublic final boolean dispatchPointerEvent(MotionEvent event) {if (event.isTouchEvent()) {return dispatchTouchEvent(event);} else {return dispatchGenericMotionEvent(event);}}

又回到DecorView的dispatchTouchEvent方法

//frameworks\base\core\java\com\android\internal\policy\DecorView.java@Overridepublic boolean dispatchTouchEvent(MotionEvent ev) {final Window.Callback cb = mWindow.getCallback();return cb != null && !mWindow.isDestroyed() && mFeatureId < 0? cb.dispatchTouchEvent(ev) : super.dispatchTouchEvent(ev);}

这里的callback就是Activity对象，调用Activity的dispatchTouchEvent方法。

//frameworks/base/core/java/android/app/Activity.javapublic boolean dispatchTouchEvent(MotionEvent ev) {if (ev.getAction() == MotionEvent.ACTION_DOWN) {onUserInteraction();}if (getWindow().superDispatchTouchEvent(ev)) {//1return true;}return onTouchEvent(ev);//2}

注释1处调用getWindow的superDispatchTouchEvent方法，getWindow返回的是一个PhoneWindow对象。注意返回值，如果返回ture的话，表明消费事件，注释2处Activity的onTouchEvent方法就不会执行。反之返回false的话使用onTouchEvent进行兜底，onTouchEvent如果是返回true，后面的InputStage就不会处理了，返回false则表明继续交给后面的InputStage处理

//frameworks/base/core/java/com/android/internal/policy/PhoneWindow.java
@Overridepublic boolean superDispatchTouchEvent(MotionEvent event) {return mDecor.superDispatchTouchEvent(event);}

又继续调用到DecorView的superDispatchTouchEvent方法

//frameworks/base/core/java/com/android/internal/policy/DecorView.java
public boolean superDispatchTouchEvent(MotionEvent event) {return super.dispatchTouchEvent(event);}

调用其父类ViewGroup的dispatchTouchEvent方法。在分析这个方法之前，先总结下事件是如何分发到ViewGroup的

事件是由DecorView分发给Activity，然后分发给window，最后又回到DecorView,再由DecorView分发给ViewGroup的。
ViewGroup接收到事件后，接下来就是将事件分发给具体的view了
ViewGroup事件分发

//frameworks/base/core/java/android/view/ViewGroup.java
@Overridepublic boolean dispatchTouchEvent(MotionEvent ev) {//省略boolean handled = false;//表明是否消费事件if (onFilterTouchEventForSecurity(ev)) {//是否符合安全策略final int action = ev.getAction();final int actionMasked = action & MotionEvent.ACTION_MASK;// Check for interception.final boolean intercepted;//是否拦截事件if (actionMasked == MotionEvent.ACTION_DOWN|| mFirstTouchTarget != null) {final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;//调用requestDisallowInterceptTouchEvent这个方法设置不允许拦截，if (!disallowIntercept) {intercepted = onInterceptTouchEvent(ev);//根据返回值判断是否允许拦截ev.setAction(action); // restore action in case it was changed} else {intercepted = false;//默认是不拦截}} else {// There are no touch targets and this action is not an initial down// so this view group continues to intercept touches.intercepted = true;//如果第一次的事件不是down的话，直接拦截}//省略// 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;//比较重要的参数if (!canceled && !intercepted) {//不拦截也不是取消事件的话进入//省略if (actionMasked == MotionEvent.ACTION_DOWN|| (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN)|| actionMasked == MotionEvent.ACTION_HOVER_MOVE) {//省略final int childrenCount = mChildrenCount;if (newTouchTarget == null && childrenCount != 0) {final float x = ev.getX(actionIndex);final float y = ev.getY(actionIndex);// Find a child that can receive the event.// Scan children from front to back.final ArrayList<View> preorderedList = buildTouchDispatchChildList();final boolean customOrder = preorderedList == null&& isChildrenDrawingOrderEnabled();final View[] children = mChildren;for (int i = childrenCount - 1; i >= 0; i--) {//遍历子iewfinal int childIndex = getAndVerifyPreorderedIndex(childrenCount, i, customOrder);final View child = getAndVerifyPreorderedView(preorderedList, children, childIndex);//省略//如果子view不能接收事件或者触摸点不在该view上的话，忽略这个viewif (!canViewReceivePointerEvents(child)|| !isTransformedTouchPointInView(x, y, child, null)) {ev.setTargetAccessibilityFocus(false);continue;}newTouchTarget = getTouchTarget(child);//取出view的TouchTarget//忽略resetCancelNextUpFlag(child);if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {//开始分发并处理了//省略newTouchTarget = addTouchTarget(child, idBitsToAssign);//进入这里表示子view消费了事件，就会设置view的TouchTarget链表，mFirstTouchTarget就不为空alreadyDispatchedToNewTouchTarget = true;//设为truebreak;}}if (preorderedList != null) preorderedList.clear();}//省略}}// 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);//注意第三个参数为null} 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) {//表明子view消费了事件handled = true;} else {final boolean cancelChild = resetCancelNextUpFlag(target.child)|| intercepted;//判断是否是取消事件if (dispatchTransformedTouchEvent(ev, cancelChild,target.child, target.pointerIdBits)) {handled = true;}//省略return handled;}

首先就是看看是不是需要拦截事件，判断是否通过requestDisallowInterceptTouchEvent这个方法，设置了ViewGroup不允许拦截，如果没有设置，再判断onInterceptTouchEvent的返回值，返回flase不表示不拦截。如果没有拦截则会遍历子view，依次使用dispatchTransformedTouchEvent处理，而如果拦截了话，也是通过dispatchTransformedTouchEvent处理，只不过传入的参数中，第3个参数为null
来看一下dispatchTransformedTouchEvent这个方法

//frameworks/base/core/java/android/view/ViewGroup.javaprivate 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);//代表取消事件的话，将action设置为ACTION_CANCELif (child == null) {handled = super.dispatchTouchEvent(event);} else {handled = child.dispatchTouchEvent(event);}event.setAction(oldAction);//又设置回来return handled;}//省略// Perform any necessary transformations and dispatch.if (child == null) {handled = super.dispatchTouchEvent(transformedEvent);//如果第三个参数传入的是空，则调用自己父类的dispatchTouchEvent方法处理} 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);//继续分发给子view处理}// Done.transformedEvent.recycle();return handled;}

dispatchTransformedTouchEvent的含义是如果child是ViewGroup的话，就继续调用ViewGroup的dispatchTouchEvent方法继续向下分发，如果child是view的话，则调用view的dispatchTouchEvent来处理事件。如果ViewGroup拦截了事件或者ViewGroup的孩子没有消费事件的话，也会调用View的dispatchTouchEvent来处理事件。来看一下view的dispatchTouchEvent方法

//frameworks/base/core/java/android/view/View.java
public boolean dispatchTouchEvent(MotionEvent event) {//省略if (onFilterTouchEventForSecurity(event)) {if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {result = true;}//noinspection SimplifiableIfStatementListenerInfo li = mListenerInfo;if (li != null && li.mOnTouchListener != null&& (mViewFlags & ENABLED_MASK) == ENABLED&& li.mOnTouchListener.onTouch(this, event)) {//设置过OnTouchListener优先调用result = true;}if (!result && onTouchEvent(event)) {//调用onTouchEvent方法result = true;}}//省略return result;}

对于事件的处理主要是判断view是不是设置过OnTouchListener，如果设置过，则调用其onTouch方法。如果OnTouch返回true的话，表示事件在这里被消费，后面的onTouchEvent就不会被调用。如果没有设置过OnTouchListener或者设置过，但是OnTouch返回false，则onTouchEvent会被调用。

上面的几个方法内容比较多，理解起来也比较费劲，用一张图总结下ViewGroup的事件分发流程

总结

• 可以通过重写ViewGroup的onInterceptTouchEvent方法来实现对事件的拦截
• 可以通过调用requestDisallowInterceptTouchEvent来禁止ViewGroup对事件拦截，这个优先级更高
• 当事件都没有被View或者ViewGroup消费的话，使用Activity的onTouchEvent进行兜底
• UP和MOVE 事件并不会重新寻找子view，而是直接分发给接收DOWN事件的view