hongxi.zhu 2023-7-21
Android 13
前面我们已经梳理了input事件在native层的传递，这一篇我们接着探索input事件在应用中的传递与处理，我们将按键事件和触摸事件分开梳理，这一篇就只涉及触摸事件。
一、事件的接收
从前面的篇幅我们知道，framework native层InputDispatcher向应用通过socket方式发送事件,应用的Looper 通过epoll方式监听sockcet的fd, 当应用的socket变为可读时（例如，inputDispatcher向socket中写入数据），Looper将回调handleEvent。 此时，应用应读取已进入套接字的事件。 只要socket中有未读事件，函数 handleEvent 就会继续触发。
NativeInputEventReceiver::handleEvent
//frameworks/base/core/jni/android_view_InputEventReceiver.cpp
int NativeInputEventReceiver::handleEvent(int receiveFd, int events, void* data) {
// Allowed return values of this function as documented in LooperCallback::handleEvent
constexpr int REMOVE_CALLBACK = 0;
constexpr int KEEP_CALLBACK = 1;
//注意：下面这个event不是真正的输入事件，只是Looper的event
if (events & (ALOOPER_EVENT_ERROR | ALOOPER_EVENT_HANGUP)) {
//当inputdispatcher异常导致socket被关闭或者目标窗口正在被移除或者传递窗口时输入法，但是输入法正在关闭时会直接抛弃这个事件
return REMOVE_CALLBACK;
}
//如果是传入的事件，即是inputDispatcher传递过来的事件时需要处理时
//回调java层的consumeEvents方法
if (events & ALOOPER_EVENT_INPUT) {
JNIEnv* env = AndroidRuntime::getJNIEnv();
status_t status = consumeEvents(env, false /*consumeBatches*/, -1, nullptr);
mMessageQueue->raiseAndClearException(env, "handleReceiveCallback");
return status == OK || status == NO_MEMORY ? KEEP_CALLBACK : REMOVE_CALLBACK;
}
//如果是要传出的事件，即已处理的事件需要告知inputdispatcher这个事件已处理时
if (events & ALOOPER_EVENT_OUTPUT) {
const status_t status = processOutboundEvents();
if (status == OK || status == WOULD_BLOCK) {
return KEEP_CALLBACK;
} else {
return REMOVE_CALLBACK;
}
}
return KEEP_CALLBACK;
}
这里既会监视inputDispatcher发送过来的事件（准确的说应该是InputPublisher发过来的）也监视当前进程发送已经消费的事件发给Looper的行为，无论是接收来自InputPublisher的事件，还是来自当前进程的事件，都会被looper监听到并回调handleEvent。这里就用events中的标志位来区分（ALOOPER_EVENT_INPUT和ALOOPER_EVENT_OUTPUT）对于接收来自InputPublisher的事件则调consumeEvents方法处理.
NativeInputEventReceiver::consumeEvents
//frameworks/base/core/jni/android_view_InputEventReceiver.cpp
status_t NativeInputEventReceiver::consumeEvents(JNIEnv* env,
bool consumeBatches, nsecs_t frameTime, bool* outConsumedBatch) {
...
ScopedLocalRef<jobject> receiverObj(env, nullptr);
bool skipCallbacks = false;
for (;;) {
uint32_t seq;
InputEvent* inputEvent;
//获取mInputConsumer发过来的事件，并构建成具体的某种InputEvent，例如MotionEvent
status_t status = mInputConsumer.consume(&mInputEventFactory,
consumeBatches, frameTime, &seq, &inputEvent);
if (status != OK && status != WOULD_BLOCK) {
ALOGE("channel '%s' ~ Failed to consume input event. status=%s(%d)",
getInputChannelName().c_str(), statusToString(status).c_str(), status);
return status;
}
...
InputConsumer::consume
//frameworks/native/libs/input/InputTransport.cpp
status_t InputConsumer::consume(InputEventFactoryInterface* factory, bool consumeBatches,
nsecs_t frameTime, uint32_t* outSeq, InputEvent** outEvent) {
...
*outSeq = 0;
*outEvent = nullptr;
// Fetch the next input message.
// Loop until an event can be returned or no additional events are received.
while (!*outEvent) {
//获取到一次真正的事件就退出
if (mMsgDeferred) {
...
} else {
// Receive a fresh message.
status_t result = mChannel->receiveMessage(&mMsg); //通过InputChannel来接收socket中真正的InputMessage(描述事件的结构体)
...
}
...
}
}
return OK;
}
InputConsumer::consume中获取事件实际上是通过InputChannel去读取
InputChannel::receiveMessage
frameworks/native/libs/input/InputTransport.cpp
status_t InputChannel::receiveMessage(InputMessage* msg) {
ssize_t nRead;
do {
nRead = ::recv(getFd(), msg, sizeof(InputMessage), MSG_DONTWAIT); //在这里真正的读取socket fd,并将输入事件信息装入msg（InputMessage)
} while (nRead == -1 && errno == EINTR);
...
return OK; //最后返回OK
}
通过InputChannel去读取真正的事件信息，并装入InputMessage对象，最后返回OK
InputChannel::receiveMessage
frameworks/native/libs/input/InputTransport.cpp
status_t InputChannel::receiveMessage(InputMessage* msg) {
ssize_t nRead;
do {
nRead = ::recv(getFd(), msg, sizeof(InputMessage), MSG_DONTWAIT); //在这里真正的读取socket fd,并将输入事件信息装入msg（InputMessage)
} while (nRead == -1 && errno == EINTR);
...
return OK; //最后返回OK
}
通过InputChannel去读取真正的事件信息，并装入InputMessage对象，最后返回OK, 然后回到前面的InputConsumer::consume
InputConsumer::consume
//frameworks/native/libs/input/InputTransport.cpp
status_t InputConsumer::consume(InputEventFactoryInterface* factory, bool consumeBatches,
nsecs_t frameTime, uint32_t* outSeq, InputEvent** outEvent) {
...
*outSeq = 0;
*outEvent = nullptr;
// Fetch the next input message.
// Loop until an event can be returned or no additional events are received.
while (!*outEvent) {
//获取到一次真正的事件就退出
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); //通过InputChannel来接收socket中真正的InputMessage(描述事件的结构体)
if (result == OK) {
mConsumeTimes.emplace(mMsg.header.seq, systemTime(SYSTEM_TIME_MONOTONIC));
}
if (result) {
//result = OK = 0 ，所以并不会进入批处理流程
// Consume the next batched event unless batches are being held for later.
...
}
}
switch (mMsg.header.type) {
...
case InputMessage::Type::MOTION: {
ssize_t batchIndex = findBatch(mMsg.body.motion.deviceId, mMsg.body.motion.source);
ALOGD("hongxi.zhu: batchIndex = %zd", batchIndex);
if (batchIndex >= 0) {
//不进行批处理
...
}
// Start a new batch if needed.
if (mMsg.body.motion.action == AMOTION_EVENT_ACTION_MOVE ||
... //不进行批处理
}
MotionEvent* motionEvent = factory->createMotionEvent(); //创建一个MotionEvent
if (!motionEvent) return NO_MEMORY;
updateTouchState(mMsg); //更新触摸的状态，记录当前的触摸信息
initializeMotionEvent(motionEvent, &mMsg); //将InputMessager转化为MotionEvent
*outSeq = mMsg.header.seq; //事件传输的seq
*outEvent = motionEvent;
break;
}
...
}
}
return OK;
}
创建并使用InputMessager中的事件信息填充MotionEvent，然后继续往下执行 NativeInputEventReceiver::consumeEvents
NativeInputEventReceiver::consumeEvents
//frameworks/base/core/jni/android_view_InputEventReceiver.cpp
status_t NativeInputEventReceiver::consumeEvents(JNIEnv* env,
bool consumeBatches, nsecs_t frameTime, bool* outConsumedBatch) {
...
for (;;) {
uint32_t seq;
InputEvent* inputEvent;
//真正的去获取socket发过来的事件，并构建成具体的某种InputEvent，例MotionEvent
status_t status = mInputConsumer.consume(&mInputEventFactory,
consumeBatches, frameTime, &seq, &inputEvent);
...
if (!skipCallbacks) {
jobject inputEventObj;
switch (inputEvent->getType()) {
case AINPUT_EVENT_TYPE_MOTION: {
MotionEvent* motionEvent = static_cast<MotionEvent*>(inputEvent);
if ((motionEvent->getAction() & AMOTION_EVENT_ACTION_MOVE) && outConsumedBatch) {
*outConsumedBatch = true;
}
//创建一个java层MotionEvent对象
inputEventObj = android_view_MotionEvent_obtainAsCopy(env, motionEvent);
break;
}
}
...
if (inputEventObj) {
...
env->CallVoidMethod(receiverObj.get(),
gInputEventReceiverClassInfo.dispatchInputEvent, seq, inputEventObj); //jni调用InputEventReceiver.java中的InputEventReceiver，将事件传递到java的世界
...
env->DeleteLocalRef(inputEventObj);
}
...
}
}
}
dispatchInputEvent
//frameworks/base/core/java/android/view/InputEventReceiver.java
public abstract class InputEventReceiver {
...
// Called from native code.
@SuppressWarnings("unused")
@UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.R, trackingBug = 170729553)
private void dispatchInputEvent(int seq, InputEvent event) {
mSeqMap.put(event.getSequenceNumber(), seq);
onInputEvent(event);
}
...
}
InputEventReceiver是一个抽象类，但是对应的dispatchInputEvent方法，它的子类WindowInputEventReceiver并没有实现，所以native层调用父类的InputEventReceiver的方法，这个方法中接着调用了onInputEvent接着处理。onInputEvent子类是有实现的，所以会走子类的方法。
onInputEvent
//frameworks/base/core/java/android/view/ViewRootImpl.java
...
final class WindowInputEventReceiver extends InputEventReceiver {
public WindowInputEventReceiver(InputChannel inputChannel, Looper looper) {
super(inputChannel, looper);
}
@Override
public void onInputEvent(InputEvent event) {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "processInputEventForCompatibility");
List<InputEvent> processedEvents;
try {
//对M版本之前的触摸事件的兼容处理
processedEvents =
mInputCompatProcessor.processInputEventForCompatibility(event);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
if (processedEvents != null) {
...
} else {
//因为上面返回null 所以走到这里
//在这里将自己this传入
//processImmediately 为true意味着需要马上处理，而不是延迟处理
enqueueInputEvent(event, this, 0, true);
}
}
...
onInputEvent中会通过QueuedInputEvent的enqueueInputEvent将事件加入队列中再处理
enqueueInputEvent
//frameworks/base/core/java/android/view/ViewRootImpl.java
@UnsupportedAppUsage
void enqueueInputEvent(InputEvent event,
InputEventReceiver receiver, int flags, boolean processImmediately) {
QueuedInputEvent q = obtainQueuedInputEvent(event, receiver, flags); //将事件加入队列，确保事件的有序处理
if (event instanceof MotionEvent) {
MotionEvent me = (MotionEvent) event;
if (me.getAction() == MotionEvent.ACTION_CANCEL) {
//inputDispatcher中会根据实际焦点和触摸坐标的关系或者事件是有down无up情形设置ACTION_CANCEL
}
} else if (event instanceof KeyEvent) {
...
}
// Always enqueue the input event in order, regardless of its time stamp.
// We do this because the application or the IME may inject key events
// in response to touch events and we want to ensure that the injected keys
// are processed in the order they were received and we cannot trust that
// the time stamp of injected events are monotonic.
// 无论时间戳如何，始终按顺序排列输入事件。
// 我们这样做是因为应用程序或 IME 可能会注入按键事件以响应触摸事件，
// 我们希望确保注入的按键按照接收到的顺序进行处理，不能仅仅通过时间戳的前后来确定顺序。
QueuedInputEvent last = mPendingInputEventTail;
if (last == null) {
mPendingInputEventHead = q;
mPendingInputEventTail = q;
} else {
last.mNext = q;
mPendingInputEventTail = q;
}
mPendingInputEventCount += 1;
Trace.traceCounter(Trace.TRACE_TAG_INPUT, mPendingInputEventQueueLengthCounterName,
mPendingInputEventCount);
if (processImmediately) {
doProcessInputEvents(); //前面传进来的processImmediately = true所以走这里处理
} else {
scheduleProcessInputEvents();
}
}
doProcessInputEvents
//frameworks/base/core/java/android/view/ViewRootImpl.java
void doProcessInputEvents() {
// Deliver all pending input events in the queue.
while (mPendingInputEventHead != null) {
QueuedInputEvent q = mPendingInputEventHead; //从队头开始处理
mPendingInputEventHead = q.mNext;
if (mPendingInputEventHead == null) {
mPendingInputEventTail = null;
}
q.mNext = null;
mPendingInputEventCount -= 1;
Trace.traceCounter(Trace.TRACE_TAG_INPUT, mPendingInputEventQueueLengthCounterName,
mPendingInputEventCount);
mViewFrameInfo.setInputEvent(mInputEventAssigner.processEvent(q.mEvent));
deliverInputEvent(q); //开始分发事件
}
// We are done processing all input events that we can process right now
// so we can clear the pending flag immediately.
//已经处理完所有待办的输入事件，是时候移除主线程mHandler中的MSG_PROCESS_INPUT_EVENTS消息了
if (mProcessInputEventsScheduled) {
mProcessInputEventsScheduled = false;
mHandler.removeMessages(MSG_PROCESS_INPUT_EVENTS);
}
}
二、事件的传递
前面将事件入队，然后在doProcessInputEvents就开始从队头拿出并通过deliverInputEvent开始分发
deliverInputEvent
//frameworks/base/core/java/android/view/ViewRootImpl.java
private void deliverInputEvent(QueuedInputEvent q) {
Trace.asyncTraceBegin(Trace.TRACE_TAG_VIEW, "deliverInputEvent",
q.mEvent.getId());
...
try {
...
InputStage stage;
if (q.shouldSendToSynthesizer()) {
stage = mSyntheticInputStage;
} else {
//如果忽略输入法窗口则从mFirstPostImeInputStage阶段开始分发，否则从mFirstInputStage开始
stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;
}
...
if (stage != null) {
handleWindowFocusChanged(); //在分发前确认是否焦点窗口变化了，如果变化就需要更新焦点的信息
stage.deliver(q); //调用对应的stage阶段的deliver方法分发事件
} else {
finishInputEvent(q);
}
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
}
把事件从拿出，下一步就是往view或者IME分发，分发的过程这里会分为多个阶段(InputStage)来顺序执行, 这些阶段在ViewRootImpl中setView时会指定
setView
//frameworks/base/core/java/android/view/ViewRootImpl.java
/**
* We have one child
*/
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView,
int userId) {
synchronized (this) {
if (mView == null) {
...
// 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);
mFirstInputStage = nativePreImeStage;
mFirstPostImeInputStage = earlyPostImeStage;
mPendingInputEventQueueLengthCounterName = "aq:pending:" + counterSuffix;
}
}
}
InputStage这里采用责任链的设计模式，从抽象类InputStage内容可以知道，每一个子类都会将next指向下一个stage子类对象
InputStage
//frameworks/base/core/java/android/view/ViewRootImpl.java
abstract class InputStage {
private final InputStage mNext;
protected static final int FORWARD = 0;
protected static final int FINISH_HANDLED = 1;
protected static final int FINISH_NOT_HANDLED = 2;
private String mTracePrefix;
/**
* Creates an input stage.
* 将所有的阶段都组成一个链表，next指向下一个阶段
* @param next The next stage to which events should be forwarded.
*/
public InputStage(InputStage next) {
mNext = next;
}
...
从setView方法中的内容，我们得出整个链条的结构
分发阶段就会从第一个创建的stage子类开始执行到最后一个stage子类,无论要不要处理，都要从链表的头传递到尾。
回到deliverInputEvent方法中stage.deliver(q)正式进入stage的分发中,观察下完整的一个stage的处理流程
//frameworks/base/core/java/android/view/ViewRootImpl.java
/**
* Delivers an event to be processed.
*/
public final void deliver(QueuedInputEvent q) {
if ((q.mFlags & QueuedInputEvent.FLAG_FINISHED) != 0) {
//如果上一stage中事件被处理（FLAG_FINISHED）那么本stage就不会再处理（onProcess），直接传递到下一个stage(无论是要处理，链表都要走完)
forward(q);
} else if (shouldDropInputEvent(q)) {
finish(q, false);
} else {
traceEvent(q, Trace.TRACE_TAG_VIEW);
final int result;
try {
result = onProcess(q); //如果前面的阶段没有被处理，本stage就需要走处理流程
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
apply(q, result); //判断是否需要下一个阶段走处理流程
}
}
/**
* Marks the input event as finished then forwards it to the next stage.
* 如果事件在当前阶段被结束，q.mFlags被标记为FLAG_FINISHED，并通过forward(q)传递给下一个阶段
*/
protected void finish(QueuedInputEvent q, boolean handled) {
q.mFlags |= QueuedInputEvent.FLAG_FINISHED;
if (handled) {
q.mFlags |= QueuedInputEvent.FLAG_FINISHED_HANDLED;
}
forward(q);
}
/**
* Forwards the event to the next stage.
* 往下一个阶段分发
*/
protected void forward(QueuedInputEvent q) {
onDeliverToNext(q);// 继续往下一个阶段传递
}
/**
* Applies a result code from {@link #onProcess} to the specified event.
* 判断是否需要继续接着往下一个阶段分发
*/
protected void apply(QueuedInputEvent q, int result) {
if (result == FORWARD) {
//如果上一个阶段还没处理这个事件，则继续往下一个阶段分发处理
forward(q);
} else if (result == FINISH_HANDLED) {
//如果事件被处理了，就标记为FLAG_FINISHED|FLAG_FINISHED_HANDLED，然后继续传递给下一个阶段（但不走onProcess()了）
finish(q, true);
} else if (result == FINISH_NOT_HANDLED) {
//如果事件没有被处理则标记为FLAG_FINISHED，然后继续传递给下一个阶段（但不走onProcess()了）
finish(q, false);
} else {
throw new IllegalArgumentException("Invalid result: " + result);
}
}
/**
* Called when an event is ready to be processed.
* @return A result code indicating how the event was handled.
*/
protected int onProcess(QueuedInputEvent q) {
return FORWARD;
}
/**
* Called when an event is being delivered to the next stage.
* 继续执行下一阶段的deliver
*/
protected void onDeliverToNext(QueuedInputEvent q) {
if (DEBUG_INPUT_STAGES) {
Log.v(mTag, "Done with " + getClass().getSimpleName() + ". " + q);
}
if (mNext != null) {
mNext.deliver(q); //如果下一阶段不为空就继续执行下一阶段的deliver，继续往下一阶段传递
} else {
finishInputEvent(q);
}
}
具体如流程图：
从NativePreImeInputStage开始deliver，事件经过每一个stage, 如果该事件没有被处理（标记为）FLAG_FINISHED或者该事件应该被抛弃（shouldDropInputEvent），那么就应该传给本阶段（stage）处理（onProcess），按照这个逻辑一直跑完整个链表。
三、View树的分发
在这里阶段里我们本篇比较关心往View树分发的阶段，即ViewPostImeInputStage
ViewPostImeInputStage
/**
* Delivers post-ime input events to the view hierarchy.
*/
final class ViewPostImeInputStage extends InputStage {
public ViewPostImeInputStage(InputStage next) {
super(next);
}
@Override
protected int onProcess(QueuedInputEvent q) {
if (q.mEvent instanceof KeyEvent) {
return processKeyEvent(q); //按键事件
} else {
final int source = q.mEvent.getSource();
if ((source & InputDevice.SOURCE_CLASS_POINTER) != 0) {
return processPointerEvent(q); //pointer类型（包含触摸事件）
} else if ((source & InputDevice.SOURCE_CLASS_TRACKBALL) != 0) {
return processTrackballEvent(q); //轨迹球
} else {
return processGenericMotionEvent(q); //其他
}
}
}
@Override
protected void onDeliverToNext(QueuedInputEvent q) {
...
super.onDeliverToNext(q);
}
private int processPointerEvent(QueuedInputEvent q) {
final MotionEvent event = (MotionEvent)q.mEvent;
mHandwritingInitiator.onTouchEvent(event);
mAttachInfo.mUnbufferedDispatchRequested = false;
mAttachInfo.mHandlingPointerEvent = true;
boolean handled = mView.dispatchPointerEvent(event); //mView实际上是DecorView, 在addView时添加
maybeUpdatePointerIcon(event);
maybeUpdateTooltip(event);
mAttachInfo.mHandlingPointerEvent = false;
if (mAttachInfo.mUnbufferedDispatchRequested && !mUnbufferedInputDispatch) {
mUnbufferedInputDispatch = true;
if (mConsumeBatchedInputScheduled) {
scheduleConsumeBatchedInputImmediately();
}
}
return handled ? FINISH_HANDLED : FORWARD;
}
...
}
回顾下继承关系：DecorView->FrameLayout->ViewGroup->View
dispatchPointerEvent方法并没有被DecorView->FrameLayout->ViewGroup实现，是祖父类View实现了这个方法
View::dispatchPointerEvent
public final boolean dispatchPointerEvent(MotionEvent event) {
if (event.isTouchEvent()) {
//根据MotionEvent事件的类型，如果是触摸事件
return dispatchTouchEvent(event); //此时是this对象是DecorView子类对象，所以调的是它的dispatchTouchEvent
} else {
//其他（如鼠标）
return dispatchGenericMotionEvent(event);
}
}
DecorView::dispatchTouchEvent
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
final Window.Callback cb = mWindow.getCallback();
//这个cb实际上是Activity对象，(当调Activity的attach方法时， 通过mWindow.setCallback(this)传入)
//这里判断条件为真，走cb.dispatchTouchEvent(ev)，也就是Activity的方法
return cb != null && !mWindow.isDestroyed() && mFeatureId < 0
? cb.dispatchTouchEvent(ev) : super.dispatchTouchEvent(ev);
}
Activity::dispatchTouchEvent
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction(); //按下时通知通知栏进行相应的变化
}
//getWindow获取到的是PhoneWindow对象(在Activity的attach方法中创建的)
//所以这里会传递给PhoneWindow::superDispatchTouchEvent
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
//如果上面的链路都没人处理，一路都是返回的false，那么最终还是由Activity来消费
return onTouchEvent(ev);
}
PhoneWindow::superDispatchTouchEvent
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
// 兜兜转转又到DecorView手里，原因就是它是View树的最顶部ViewGroup呀，还是得从它开始的
return mDecor.superDispatchTouchEvent(event);
}
DecorView::superDispatchTouchEvent
public boolean superDispatchTouchEvent(MotionEvent event) {
//调用父类ViewGroup的dispatchTouchEvent开始遍历子成员分发
return super.dispatchTouchEvent(event);
}
ViewGroup::dispatchTouchEvent
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
...
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
final int action = ev.getAction();
final int actionMasked = action & MotionEvent.ACTION_MASK;
// Handle an initial down.
//如果这是个ACTION_DOWN事件说明是一个新触摸行为的开始，那么重置相关的状态
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.
//ViewGroup是否拦截当前事件，通过onInterceptTouchEvent方法。这个方法只有ViewGroup有
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;
}
...
if (!canceled && !intercepted) {
//当这时一个ACTION_DOWN事件进这里
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 (newTouchTarget == null && childrenCount != 0) {
final float x =
isMouseEvent ? ev.getXCursorPosition() : ev.getX(actionIndex);
final float y =
isMouseEvent ? ev.getYCursorPosition() : ev.getY(actionIndex);
// Find a child that can receive the event.
// Scan children from front to back.
//在当前ViewGroup中找到能处理这个事件的子View或者Viewgroup
final ArrayList<View> preorderedList = buildTouchDispatchChildList();
final boolean customOrder = preorderedList == null
&& isChildrenDrawingOrderEnabled();
final View[] children = mChildren;
for (int i = childrenCount - 1; i >= 0; i--) {
final int childIndex = getAndVerifyPreorderedIndex(
childrenCount, i, customOrder);
final View child = getAndVerifyPreorderedView(
preorderedList, children, childIndex);
....
newTouchTarget = getTouchTarget(child);
resetCancelNextUpFlag(child);
//传递到child，调用dispatchTouchEvent，或者如果当前ViewGroup没有child，则调用View的dispatchTouchEvent交由当前ViewGroup处理
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
// Child wants to receive touch within its bounds.
...
mLastTouchDownX = ev.getX();
mLastTouchDownY = ev.getY();
//记录下这个能消费触摸事件的View target
newTouchTarget = addTouchTarget(child, idBitsToAssign);
alreadyDispatchedToNewTouchTarget = true; //这个标识通过这个Down事件找到了能处理这个触摸行为的View target
break;
}
// The accessibility focus didn't handle the event, so clear
// the flag and do a normal dispatch to all children.
ev.setTargetAccessibilityFocus(false);
}
if (preorderedList != null) preorderedList.clear();
}
...
}
}
// Dispatch to touch targets.
if (mFirstTouchTarget == null) {
// No touch targets so treat this as an ordinary view.
//如果找不到mFirstTouchTarget，则交给当前ViewGroup处理，即通过super.dispatchTouchEvent(event)
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) {
//前面的dispatchTransformedTouchEvent已经处理了这个Down事件,直接标识为已消费
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
//如果被拦截，则给子child发ACTION_CANCEL事件
//如果没有拦截则正常分发到子类，包括MOVE和UP事件
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;
}
}
...
return handled;
}
ViewGroup::dispatchTransformedTouchEvent
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
final boolean handled;
...
final MotionEvent transformedEvent;
if (newPointerIdBits == oldPointerIdBits) {
if (child == null || child.hasIdentityMatrix()) {
if (child == null) {
//如果当前ViewGroup没有子View或者子ViewGroup，则调用View的dispatchTouchEvent，即由当前ViewGroup来处理
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); //由子View或者子ViewGroup的dispatchTouchEvent处理
event.offsetLocation(-offsetX, -offsetY);
}
return handled;
}
transformedEvent = MotionEvent.obtain(event);
} else {
transformedEvent = event.split(newPointerIdBits);
}
...
return handled;
}
View::dispatchTouchEvent
public boolean dispatchTouchEvent(MotionEvent event) {
...
if (onFilterTouchEventForSecurity(event)) {
...
//noinspection SimplifiableIfStatement
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
//如果实现了onTouch方法，则不往下执行
result = true;
}
if (!result && onTouchEvent(event)) {
//调用当前View的onTouchEvent(这个View可能是View也可能是ViewGroup)
result = true;
}
}
...
return result;
}
View::onTouchEvent
public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction();
final boolean clickable = ((viewFlags & CLICKABLE) == CLICKABLE
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE;
...
if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
//根据action进行处理
switch (action) {
case MotionEvent.ACTION_UP:
...
break;
case MotionEvent.ACTION_DOWN:
...
break;
case MotionEvent.ACTION_CANCEL:
...
break;
case MotionEvent.ACTION_MOVE:
...
break;
}
return true;
}
return false;
}
这个方法也是又臭又长，核心方法了, 还是用图来说明更直接，也结束触摸事件的分析。
参考：https://blog.csdn.net/moliao2046/article/details/103737611