Android7 Input（十一）App View InputEvent事件分发
概述
本文主要讲述App View中inputEvent事件分发的流程，我们这里不讲述关于Android View窗口管理系统。Android系统中View的事件分发的方向就是:
Activity -> PhoneWindow -> DecorView -> ViewGroup -> View
当事件被处理完成后，根据事件处理的结果然，反向调用路径返回：
从View-> ViewGroup->DecorView->PhoneWindow->Activity
本文涉及的源码路径
frameworks/base/core/java/android/view/ViewRootImpl.java
frameworks/base/core/java/android/view/View.java
事件分发
上篇我们讲了，事件分发过程中，会找到目标View开始分发，如下代码所示:
private int processPointerEvent(QueuedInputEvent q) {
final MotionEvent event = (MotionEvent)q.mEvent;
mAttachInfo.mUnbufferedDispatchRequested = false;
final View eventTarget =
(event.isFromSource(InputDevice.SOURCE_MOUSE) && mCapturingView != null) ?
mCapturingView : mView;
mAttachInfo.mHandlingPointerEvent = true;
boolean handled = eventTarget.dispatchPointerEvent(event);
maybeUpdatePointerIcon(event);
mAttachInfo.mHandlingPointerEvent = false;
if (mAttachInfo.mUnbufferedDispatchRequested && !mUnbufferedInputDispatch) {
mUnbufferedInputDispatch = true;
if (mConsumeBatchedInputScheduled) {
scheduleConsumeBatchedInputImmediately();
}
}
return handled ? FINISH_HANDLED : FORWARD;
}继续调用View中的dispatchPointerEvent方法，如下所示:
public final boolean dispatchPointerEvent(MotionEvent event) {
if (event.isTouchEvent()) {
return dispatchTouchEvent(event);
} else {
return dispatchGenericMotionEvent(event);
}
}然后调用dispacthTouchEvent方法，开始从顶层的Activity一层一层，向能接受输入事件的view进行处理，为什么时Activity中的dispacthTouchEvent方法，这里不再追踪原因，感兴趣的同学可以学习一下Android系统中的窗口管理相关的知识。
1、Activity中的事件分发
Activity中事件分发，如下所示:
public boolean dispatchTouchEvent(MotionEvent ev) {
Log.i(TAG, "dispatchTouchEvent");
if (ev.getAction() == MotionEvent.ACTION_DOWN) {
onUserInteraction();
}
// 调用子类实现PhoneWindow中的superDispatchTouchEvent()
if (getWindow().superDispatchTouchEvent(ev)) {
return true;
}
return onTouchEvent(ev);
}该方法的核心逻辑如下:
a. 调用PhoneWindow中的superDispatchTouchEvent进行分发；
b. 如果事件在PhoneWindow中没有被处理，则调用Activty自己的onTouchEvent方法，默认返回false, 表示事件没有被处理;
2、PhoneWindow中的事件分发
PhoneWindow中调用比较简单，直接交给DecorView处理，如下所示:
@Override
public boolean superDispatchTouchEvent(MotionEvent event) {
Log.i(TAG, "superDispatchTouchEvent");
return mDecor.superDispatchTouchEvent(event);
}3、DecorView中的事件分发
DecorView中也不直接处理，而是调用父类的dispatchTouchEvent处理，如下所示:
public boolean superDispatchTouchEvent(MotionEvent event) {
Log.i(TAG, "superDispatchTouchEvent");
return super.dispatchTouchEvent(event);
}4、ViewGroup中的事件分发
第3步中，事件由DecorView中父类处理，DecorView的父类为FrameLayout，FrageLayout继承ViewGroup,我们从FrameLayout中没有找到dispatchTouchEvent, 再次向上找父类，从ViewGroup中找到了dispatchTouchEvent方法，饶了一圈，最终调用到了ViewGroup中的dispatchTouchEvent如下所示:
public boolean dispatchTouchEvent(MotionEvent ev) {
......
boolean handled = false;
if (onFilterTouchEventForSecurity(ev)) {
......
// Check for interception.
// 检查事件是否可以被拦截
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.
// 如果当前事件没有处理它的子view，也不是ACTION_DOWN事件，则父类拦截
intercepted = true;
}
......
//如果没取消和拦截
if (!canceled && !intercepted) {
......
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.
// 找到一个能接受事件的子view
// 按照显示在最上层到最下层的顺序去遍历
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);
// canViewReceivePointerEvents方法判断子view是否visible或者子view是否在播动画或者即将播动画
// isTransformedTouchPointInView方法判断点击区域是否处于子view内
if (!canViewReceivePointerEvents(child)
|| !isTransformedTouchPointInView(x, y, child, null)) {
ev.setTargetAccessibilityFocus(false);
continue;
}
//dispatchTransformedTouchEvent方法是真正把事件分发给子view处理的
// 返回值为true则代表该子view处理了事件
if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) {
......
}
}
......
TouchTarget target = mFirstTouchTarget;
while (target != null) {
final TouchTarget next = target.next;
if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) {
handled = true;
} else {
final boolean cancelChild = resetCancelNextUpFlag(target.child)
|| intercepted;
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;
}该方法事件比较复杂，我为了简化事件分发流程，我在这个只保留了最核心的实现，该方法的实现逻辑如下:
1、遍历ViewGroup中的view,找到能接受input事件的View;
2、调用dispatchTransformedTouchEvent()进行事件处理；
3、返回事件处理的结果handled;
5、View中的事件分发
当找到能接受输入事件的子View后，调用dispatchTransformedTouchEvent进入事件的进一步分发，如下所示:
private boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel,
View child, int desiredPointerIdBits) {
......
final int oldAction = event.getAction();
if (cancel || oldAction == MotionEvent.ACTION_CANCEL) {
event.setAction(MotionEvent.ACTION_CANCEL);
if (child == null) {
//如果子view为空,直接调了ViewGroup的父类View的dispatchTouchEvent方法
handled = super.dispatchTouchEvent(event);
} else {
//如果子view不等于空,调用子view的dispatchTouchEvent方法
//如果子view是一个ViewGroup，则递归ViewGroup的dispatchTouchEvent方法，重复上面分析的逻辑
//如果子view是普通的view，则事件分发到View的dispatchTouchEvent方法
handled = child.dispatchTouchEvent(event);
}
event.setAction(oldAction);
return handled;
}
......
}该方法中直接执行view中的dispatchTouchEvent方法，这里有一种ViewGroup嵌套的情况下，则继续重复之前的流程，为了简化描述流程，我们这里假设找到最后的孩子view(比如Button)。 然后调用dispatchTouchEvent如下所示:
public boolean dispatchTouchEvent(MotionEvent event) {
// If the event should be handled by accessibility focus first.
if (event.isTargetAccessibilityFocus()) {
......
if (onFilterTouchEventForSecurity(event)) {
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
//noinspection SimplifiableIfStatement
// 已经注册了onToucherListenero监听，不再调用onTouchEvent处理
ListenerInfo li = mListenerInfo;
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
//只有result为false事件才分发到onTouchEvent
if (!result && onTouchEvent(event)) {
result = true;
}
}
......
return result;
}我们这里假设没有注册touch监听，则调用view中的onTouchEvent方法，如下所示:
public boolean onTouchEvent(MotionEvent event) {
final float x = event.getX();
final float y = event.getY();
final int viewFlags = mViewFlags;
final int action = event.getAction();
if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
(viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) {
switch (action) {
case MotionEvent.ACTION_UP:
......
if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
// This is a tap, so remove the longpress check
removeLongPressCallback();
// Only perform take click actions if we were in the pressed state
if (!focusTaken) {
// Use a Runnable and post this rather than calling
// performClick directly. This lets other visual state
// of the view update before click actions start.
//调用OnClickListener的onClick方法
if (mPerformClick == null) {
mPerformClick = new PerformClick();
}
if (!post(mPerformClick)) {
performClick();
}
}
}
......
case MotionEvent.ACTION_DOWN:
......
if (isInScrollingContainer) {
mPrivateFlags |= PFLAG_PREPRESSED;
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPendingCheckForTap.x = event.getX();
mPendingCheckForTap.y = event.getY();
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
} else {
// Not inside a scrolling container, so show the feedback right away
setPressed(true, x, y);
checkForLongClick(0, x, y);
}
break;
}
return true;
}
return false;
}该方法的最终调用performClick让控件去处理事件，如下所示:
public boolean performClick() {
final boolean result;
final ListenerInfo li = mListenerInfo;
if (li != null && li.mOnClickListener != null) {
playSoundEffect(SoundEffectConstants.CLICK);
li.mOnClickListener.onClick(this);
result = true;
} else {
result = false;
}
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
return result;
}最后，调用到了onClick方法，回调App对输入事件的处理接口，事件在这里就到了它最终的到达的地方。我们不再展开讲述如果在这条路径上，如果事件没有被处理的情况。
总结
本文主要描述了，Android View事件分发被处理的流程，在讲述过程中，为了简化，我们删除了很多细节的东西。因为讲述Android View Input事件不能单独拿出来讲述，因为涉及的内容比较多，希望以后自己能力达到了，再补充上我删除的部分,Android 7 Input 子系统的框架梳理到此为止，下一个专题Android HAL层开发;