Android事件分发的事件从何而来
事件分发一直以来都是一个android知识的重点。从应用开发角度和用户的交互就是在处理事件。
Activity的事件分发
事件分发一般情况都会讲view的分发过程，他的过程缩略起来就可以这样表示。
public boolean diapatchTouchEvent(MotionEvent ev) {
boolean consume = false;
if (onInterceptTouchEvent(ev)) {
consume = onTouchEvent(ev);
} else {
consume = child.dispatchTouchEvent(ev);
}
return consume;
}
这里就有一个问题，最早的事件是从哪里来的。根据Android的视图模型知道最外层的view就是DecorView ,而它的外面是一个PhoneWindow。所以最初的事件就是从PhoneWindow进入了view的事件分发，而PhoneWindow的事件又是Activity中来的.
//frameworks/base/core/java/android/app/Activity.java
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {//这里获取的PhoneWindow
return true;
}
return onTouchEvent(ev);
}
那么问题又来了，activity的事件是哪里来的呢。
ViewRootImpl事件分发
熟悉Android的Window创建流程的话就知道ViewRootImpl是所有view的最顶层。也是ViewRootImpl在setView中实现了View和WindowManager之间的交互。这个方法里有一个在Window创建流程的时候没有关注的InputChannel，事件真正的来源就是它，在
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView,
int userId) {
synchronized (this) {
if (mView == null) {
mView = view;
.........
InputChannel inputChannel = null;//创建InputChannel
if ((mWindowAttributes.inputFeatures
& WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
inputChannel = new InputChannel();
}
res = mWindowSession.addToDisplayAsUser(mWindow, mWindowAttributes,
getHostVisibility(), mDisplay.getDisplayId(), userId,
mInsetsController.getRequestedVisibilities(), inputChannel, mTempInsets,mTempControls, attachedFrame, sizeCompatScale);//将InputChannel传给WMS
if (inputChannel != null) {
if (mInputQueueCallback != null) {
mInputQueue = new InputQueue();
mInputQueueCallback.onInputQueueCreated(mInputQueue);
}
mInputEventReceiver = new WindowInputEventReceiver(inputChannel,
Looper.myLooper());//创建mInputEventReceiver
}
//这里创建了各种事件处理器
// 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;
AnimationHandler.requestAnimatorsEnabled(mAppVisible, this);
}
}
}
从名字也能猜出mInputEventReceiver就是接收事件的对象了，这是一个ViewRootImpl的内部类看下它的实现。
final class WindowInputEventReceiver extends InputEventReceiver {
public WindowInputEventReceiver(InputChannel inputChannel, Looper looper) {
super(inputChannel, looper);
}
@Override
public void onInputEvent(InputEvent event) {//通过名字就知道这应该是事件接收的回调
List processedEvents;
try {
processedEvents =
mInputCompatProcessor.processInputEventForCompatibility(event);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
if (processedEvents != null) {
if (processedEvents.isEmpty()) {
// InputEvent consumed by mInputCompatProcessor
finishInputEvent(event, true);
} else {
for (int i = 0; i < processedEvents.size(); i++) {
enqueueInputEvent(
processedEvents.get(i), this,
QueuedInputEvent.FLAG_MODIFIED_FOR_COMPATIBILITY, true);
}
}
} else {
enqueueInputEvent(event, this, 0, true);
}
}
.......
}
如果processedEvents不为空都是调用了enqueueInputEvent，不然就直接调用finishInputEvent。
void enqueueInputEvent(InputEvent event,
InputEventReceiver receiver, int flags, boolean processImmediately) {
QueuedInputEvent q = obtainQueuedInputEvent(event, receiver, flags);
//这里做了区分是触摸事件还是按键事件
if (event instanceof MotionEvent) {
MotionEvent me = (MotionEvent) event;
} else if (event instanceof KeyEvent) {
KeyEvent ke = (KeyEvent) event;
}
QueuedInputEvent last = mPendingInputEventTail;
if (last == null) {
mPendingInputEventHead = q;
mPendingInputEventTail = q;
} else {
last.mNext = q;
mPendingInputEventTail = q;
}
mPendingInputEventCount += 1;
if (processImmediately) {
doProcessInputEvents();
} else {
scheduleProcessInputEvents();
}
}
private void scheduleProcessInputEvents() {
if (!mProcessInputEventsScheduled) {
mProcessInputEventsScheduled = true;
Message msg = mHandler.obtainMessage(MSG_PROCESS_INPUT_EVENTS);
msg.setAsynchronous(true);
mHandler.sendMessage(msg);
}
}
private void handleMessageImpl(Message msg) {
switch (msg.what) {
case MSG_PROCESS_INPUT_EVENTS:
mProcessInputEventsScheduled = false;
doProcessInputEvents();
}
}
这里判断了是否要立即消费，如果立即消费doProcessInputEvents，不然调用scheduleProcessInputEvents。而scheduleProcessInputEvents很简单就是handle发送了一个异步消息。最后handle执行的时候还是会调用到doProcessInputEvents。所以就来详细看下doProcessInputEvents。
void doProcessInputEvents() {
// Deliver all pending input events in the queue.
while (mPendingInputEventHead != null) {//循环获取InputEvent并处理
QueuedInputEvent q = mPendingInputEventHead;
mPendingInputEventHead = q.mNext;
if (mPendingInputEventHead == null) {
mPendingInputEventTail = null;
}
q.mNext = null;
mPendingInputEventCount -= 1;
mViewFrameInfo.setInputEvent(mInputEventAssigner.processEvent(q.mEvent));
deliverInputEvent(q);
}
//移除异步消息
if (mProcessInputEventsScheduled) {
mProcessInputEventsScheduled = false;
mHandler.removeMessages(MSG_PROCESS_INPUT_EVENTS);
}
}
可以看到真实的处理都是deliverInputEvent来处理。
private void deliverInputEvent(QueuedInputEvent q) {
try {
if (mInputEventConsistencyVerifier != null) {
InputStage stage;//在ViewRootImpl的setView中初始化的处理器
if (q.shouldSendToSynthesizer()) {
stage = mSyntheticInputStage;
} else {
stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;
}
if (q.mEvent instanceof KeyEvent) {
try {
mUnhandledKeyManager.preDispatch((KeyEvent) q.mEvent);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
}
if (stage != null) {
handleWindowFocusChanged();
stage.deliver(q);
} else {
finishInputEvent(q);
}
} finally {
}
}
在deliverInputEvent中出现了stage，这就是在setView初始化的那些处理器，处理通过stage.deliver(q)来实现。 InputStage 还是ViewRootImpl的一个内部类。
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;
public InputStage(InputStage next) {
mNext = next;
}
public final void deliver(QueuedInputEvent q) {
//分发事件
if ((q.mFlags & QueuedInputEvent.FLAG_FINISHED) != 0) {
forward(q);
} else if (shouldDropInputEvent(q)) {
finish(q, false);
} else {
traceEvent(q, Trace.TRACE_TAG_VIEW);
final int result;
try {
result = onProcess(q);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
apply(q, result);
}
}
//处理事件由子类改写
protected int onProcess(QueuedInputEvent q) {
return FORWARD;
}
protected void finish(QueuedInputEvent q, boolean handled) {
q.mFlags |= QueuedInputEvent.FLAG_FINISHED;
if (handled) {
q.mFlags |= QueuedInputEvent.FLAG_FINISHED_HANDLED;
}
forward(q);
}
protected void forward(QueuedInputEvent q) {
onDeliverToNext(q);
}
protected void onDeliverToNext(QueuedInputEvent q) {
//向后一个 InputStage 传递事件
if (mNext != null) {
mNext.deliver(q);
} else {
finishInputEvent(q);
}
}
}
熟悉okhttp的话很容易就发现这里也是一个责任链模式。从setView中 InputStage 子类的初始化也能看到，其中和view相关的是ViewPostImeInputStage。
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);
} else {
final int source = q.mEvent.getSource();
//判断事件类型，触摸事件会进入processPointerEvent
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);
}
}
}
private int processPointerEvent(QueuedInputEvent q) {
final MotionEvent event = (MotionEvent)q.mEvent;
mHandwritingInitiator.onTouchEvent(event);
mAttachInfo.mUnbufferedDispatchRequested = false;
mAttachInfo.mHandlingPointerEvent = true;
//通过mView的dispatchPointerEvent来分发事件
boolean handled = mView.dispatchPointerEvent(event);
maybeUpdatePointerIcon(event);
maybeUpdateTooltip(event);
mAttachInfo.mHandlingPointerEvent = false;
if (mAttachInfo.mUnbufferedDispatchRequested && !mUnbufferedInputDispatch) {
mUnbufferedInputDispatch = true;
if (mConsumeBatchedInputScheduled) {
scheduleConsumeBatchedInputImmediately();
}
}
return handled ? FINISH_HANDLED : FORWARD;
}
ViewRootImpl的事件就交给mView来继续分发了，这里mView是DecorView，也是在setView中传进来的。
DecorView事件处理
//frameworks/base/core/java/android/view/View.java
@UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.R, trackingBug = 170729553)
public final boolean dispatchPointerEvent(MotionEvent event) {
if (event.isTouchEvent()) {
return dispatchTouchEvent(event);
} else {
return dispatchGenericMotionEvent(event);
}
}
//frameworks/base/core/java/com/android/internal/policy/DecorView.java
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
final Window.Callback cb = mWindow.getCallback();
return cb != null && !mWindow.isDestroyed() && mFeatureId < 0
? cb.dispatchTouchEvent(ev) : super.dispatchTouchEvent(ev);
}
这里通过dispatchTouchEvent将事件交给了Window.Callback，而这里的Window.Callback就是Activity，兜兜转转终于回到了Activity的dispatchTouchEvent中。
通过这个流程可以知道，事件的流程是WMS->ViewRootImpl->DecorView->Activity->PhoneWindow->DecorView，这里有一个疑问就是为什么不直接从DecorView开始分发。我猜测是为了方便在应用层重写Activity中的onTouch来消费没有view处理的事件。
现在还有一个疑问是WMS的事件是怎么来的，这个留着后续再分析。
以上就是Android事件分发事件由来初识的详细内容，更多关于Android事件分发事件由来的资料请关注脚本之家其它相关文章！