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本篇內容主要講解“Andriod事件分發事件怎么來的”，感興趣的朋友不妨來看看。本文介紹的方法操作簡單快捷，實用性強。下面就讓小編來帶大家學習“Andriod事件分發事件怎么來的”吧!
事件分發一直以來都是一個android知識的重點。從應用開發角度和用戶的交互就是在處理事件。
事件分發一般情況都會講view的分發過程，他的過程縮略起來就可以這樣表示。
public boolean diapatchTouchEvent(MotionEvent ev) {
boolean consume = false;
if (onInterceptTouchEvent(ev)) {
consume = onTouchEvent(ev);
} else {
consume = child.dispatchTouchEvent(ev);
}
return consume;
}這里就有一個問題，最早的事件是從哪里來的。根據Android的視圖模型知道最外層的view就是DecorView ,而它的外面是一個PhoneWindow。所以最初的事件就是從PhoneWindow進入了view的事件分發，而PhoneWindow的事件又是Activity中來的.
//frameworks/base/core/java/android/app/Activity.java
public boolean dispatchTouchEvent(MotionEvent ev) {
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
if (getWindow().superDispatchTouchEvent(ev)) {//這里獲取的PhoneWindow
return true;
}
return onTouchEvent(ev);
}那么問題又來了，activity的事件是哪里來的呢。
熟悉Android的Window創建流程的話就知道ViewRootImpl是所有view的最頂層。也是ViewRootImpl在setView中實現了View和WindowManager之間的交互。這個方法里有一個在Window創建流程的時候沒有關注的InputChannel，事件真正的來源就是它，在
public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView,
int userId) {
synchronized (this) {
if (mView == null) {
mView = view;
.........
InputChannel inputChannel = null;//創建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);//將InputChannel傳給WMS
if (inputChannel != null) {
if (mInputQueueCallback != null) {
mInputQueue = new InputQueue();
mInputQueueCallback.onInputQueueCreated(mInputQueue);
}
mInputEventReceiver = new WindowInputEventReceiver(inputChannel,
Looper.myLooper());//創建mInputEventReceiver
}
//這里創建了各種事件處理器
// 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);
}
}
}從名字也能猜出mInputEventReceiver就是接收事件的對象了，這是一個ViewRootImpl的內部類看下它的實現。
final class WindowInputEventReceiver extends InputEventReceiver {
public WindowInputEventReceiver(InputChannel inputChannel, Looper looper) {
super(inputChannel, looper);
}
@Override
public void onInputEvent(InputEvent event) {//通過名字就知道這應該是事件接收的回調
List<InputEvent> 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不為空都是調用了enqueueInputEvent，不然就直接調用finishInputEvent。
void enqueueInputEvent(InputEvent event,
InputEventReceiver receiver, int flags, boolean processImmediately) {
QueuedInputEvent q = obtainQueuedInputEvent(event, receiver, flags);
//這里做了區分是觸摸事件還是按鍵事件
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();
}
}這里判斷了是否要立即消費，如果立即消費doProcessInputEvents，不然調用scheduleProcessInputEvents。而scheduleProcessInputEvents很簡單就是handle發送了一個異步消息。最后handle執行的時候還是會調用到doProcessInputEvents。所以就來詳細看下doProcessInputEvents。
void doProcessInputEvents() {
// Deliver all pending input events in the queue.
while (mPendingInputEventHead != null) {//循環獲取InputEvent并處理
QueuedInputEvent q = mPendingInputEventHead;
mPendingInputEventHead = q.mNext;
if (mPendingInputEventHead == null) {
mPendingInputEventTail = null;
}
q.mNext = null;
mPendingInputEventCount -= 1;
mViewFrameInfo.setInputEvent(mInputEventAssigner.processEvent(q.mEvent));
deliverInputEvent(q);
}
//移除異步消息
if (mProcessInputEventsScheduled) {
mProcessInputEventsScheduled = false;
mHandler.removeMessages(MSG_PROCESS_INPUT_EVENTS);
}
}可以看到真實的處理都是deliverInputEvent來處理。
private void deliverInputEvent(QueuedInputEvent q) {
try {
if (mInputEventConsistencyVerifier != null) {
InputStage stage;//在ViewRootImpl的setView中初始化的處理器
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中出現了stage，這就是在setView初始化的那些處理器，處理通過stage.deliver(q)來實現。 InputStage 還是ViewRootImpl的一個內部類。
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) {
//分發事件
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);
}
}
//處理事件由子類改寫
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) {
//向后一個 InputStage 傳遞事件
if (mNext != null) {
mNext.deliver(q);
} else {
finishInputEvent(q);
}
}
}熟悉okhttp的話很容易就發現這里也是一個責任鏈模式。從setView中 InputStage 子類的初始化也能看到，其中和view相關的是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();
//判斷事件類型，觸摸事件會進入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;
//通過mView的dispatchPointerEvent來分發事件
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的事件就交給mView來繼續分發了，這里mView是DecorView，也是在setView中傳進來的。
//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);
}這里通過dispatchTouchEvent將事件交給了Window.Callback，而這里的Window.Callback就是Activity，兜兜轉轉終于回到了Activity的dispatchTouchEvent中。
通過這個流程可以知道，事件的流程是WMS->ViewRootImpl->DecorView->Activity->PhoneWindow->DecorView，這里有一個疑問就是為什么不直接從DecorView開始分發。我猜測是為了方便在應用層重寫Activity中的onTouch來消費沒有view處理的事件。
到此，相信大家對“Andriod事件分發事件怎么來的”有了更深的了解，不妨來實際操作一番吧！這里是億速云網站，更多相關內容可以進入相關頻道進行查詢，關注我們，繼續學習！
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