点击事件是如何传递给Activity的

事件从Window传递给Activity,在windowgloble的addview方法中会创建InputChannel、InputQueue和WindowInputEventReceiver来接受点击事件的消息。

ViewRootImpl中有个方法

private void scheduleProcessInputEvents() {
if (!mProcessInputEventsScheduled) {
mProcessInputEventsScheduled = true;
Message msg = mHandler.obtainMessage(MSG_PROCESS_INPUT_EVENTS);
msg.setAsynchronous(true);
mHandler.sendMessage(msg);
}
}

我们看是如何被处理的

case MSG_PROCESS_INPUT_EVENTS:
mProcessInputEventsScheduled = false;
doProcessInputEvents();
break;

会调用doProcessInputEvents方法

void doProcessInputEvents() {
// Deliver all pending input events in the queue.
while (mPendingInputEventHead != null) {
QueuedInputEvent q = mPendingInputEventHead;
mPendingInputEventHead = q.mNext;
if (mPendingInputEventHead == null) {
mPendingInputEventTail = null;
}
q.mNext = null;

mPendingInputEventCount -= 1;
Trace.traceCounter(Trace.TRACE_TAG_INPUT, mPendingInputEventQueueLengthCounterName,
mPendingInputEventCount);

deliverInputEvent(q);
}

private void deliverInputEvent(QueuedInputEvent q) {
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "deliverInputEvent");
try {
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onInputEvent(q.mEvent, 0);
}

InputStage stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;
if (stage != null) {
stage.deliver(q);
} else {
finishInputEvent(q);
}
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
}

在ViewRootImpl中，有一系列类似于InputStage（输入事件舞台）的概念，每种InputStage可以处理一定的事件类型，比如AsyncInputStage、ViewPreImeInputStage、ViewPostImeInputStage等。当一个InputEvent到来时，ViewRootImpl会寻找合适它的InputStage来处理。对于点击事件来说，ViewPostImeInputStage可以处理它，ViewPostImeInputStage中，有一个processPointerEvent方法，如下，它会调用mView的dispatchPointerEvent方法，注意，这里的mView其实就是DecorView。

private int processPointerEvent(QueuedInputEvent q) {
final MotionEvent event = (MotionEvent)q.mEvent;

// 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);
}

// Remember the touch position for possible drag-initiation.
if (event.isTouchEvent()) {
mLastTouchPoint.x = event.getRawX();
mLastTouchPoint.y = event.getRawY();
}
return FORWARD;
}

我们看View中的dispatchPointerEvent，因为DecorView继承自View

public final boolean dispatchPointerEvent(MotionEvent event) {
if (event.isTouchEvent()) {
return dispatchTouchEvent(event);
} else {
return dispatchGenericMotionEvent(event);
}
}

然后调用了DecorView的dispatchTouchEvent

@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
final Callback cb = getCallback();
return cb != null && !isDestroyed() && mFeatureId < 0 ? cb.dispatchTouchEvent(ev)
: super.dispatchTouchEvent(ev);
}

这里的cb就是Activity对象。