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概述

上一个章节，我们讲解了App通过注册InputEventReceiver获取从Input服务上报的输入事件的流程，在讲述App处理具体输入事件之前，我们讲述App处理输入事件的模型，也就是本章要讲述的InputState Pipeline。

源码路径

frameworks/base/core/java/android/view/ViewRootImpl.java

Input事件处理模型

View Input事件处理的Pipeline模型建立在InputStage这个抽象接口基础之上，我们这里先讲述InputStage的实现，我们只列出InputStage的核心接口实现，如下所示:

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;public InputStage(InputStage next) {mNext = next;}public final void deliver(QueuedInputEvent q) {if ((q.mFlags & QueuedInputEvent.FLAG_FINISHED) != 0) {forward(q);} else if (shouldDropInputEvent(q)) {finish(q, false);} else {apply(q, onProcess(q));}}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 apply(QueuedInputEvent q, int result) {if (result == FORWARD) {forward(q);} else if (result == FINISH_HANDLED) {finish(q, true);} else if (result == FINISH_NOT_HANDLED) {finish(q, false);} else {throw new IllegalArgumentException("Invalid result: " + result);}}protected int onProcess(QueuedInputEvent q) {return FORWARD;}protected void onDeliverToNext(QueuedInputEvent q) {if (DEBUG_INPUT_STAGES) {Log.v(mTag, "Done with " + getClass().getSimpleName() + ". " + q);}if (mNext != null) {mNext.deliver(q);} else {finishInputEvent(q);}}}

1、deliver的实现，因为他决定input事件处理方式方法实现如下:

 public final void deliver(QueuedInputEvent q) {if ((q.mFlags & QueuedInputEvent.FLAG_FINISHED) != 0) {forward(q);} else if (shouldDropInputEvent(q)) {finish(q, false);} else {apply(q, onProcess(q));}}

deliver的核心逻辑，如下所示:

a、当前input事件直接被转发到下一级的InputStage进行处理 forward;

b、如果input事件在当前InputStage中被丢弃了，直接设置input事件被处理完成标记，并转发给下一级的InputStage；

c、当前InputStage进行处理调用process方法，然后根据处理的结果，决定input输入事件，是否向下一级的InputStage进行处理;

2、finish的实现非常简单，将事件打上FINISHED标签，然后转发；

 protected void finish(QueuedInputEvent q, boolean handled) {q.mFlags |= QueuedInputEvent.FLAG_FINISHED;if (handled) {q.mFlags |= QueuedInputEvent.FLAG_FINISHED_HANDLED;}// 当前InputStage不再处理，直接转发forward(q);}

3、forward 转发给下一级的InputStage处理

protected void forward(QueuedInputEvent q) {onDeliverToNext(q);}

4、apply 根据result结果，其本质也就是调用onProcess的返回结果，然后决定input事件下一步的处理方式。

protected void apply(QueuedInputEvent q, int result) {if (result == FORWARD) {forward(q);} else if (result == FINISH_HANDLED) {finish(q, true);} else if (result == FINISH_NOT_HANDLED) {finish(q, false);} else {throw new IllegalArgumentException("Invalid result: " + result);}
}

5、onProcess 的默认行为是转发。子类可以覆盖其实现，决定input事件的处理方式;

 protected int onProcess(QueuedInputEvent q) {return FORWARD;}

6、onDeliverToNext 直接转发给下一级的InputStage进行处理

 protected void onDeliverToNext(QueuedInputEvent q) {if (DEBUG_INPUT_STAGES) {Log.v(mTag, "Done with " + getClass().getSimpleName() + ". " + q);}if (mNext != null) {mNext.deliver(q);} else {finishInputEvent(q);}}

7、finishInputEvent 结束事件的处理流程。然后直接将处理结果返回给InputEventReceiver处理。

private void finishInputEvent(QueuedInputEvent q) {Trace.asyncTraceEnd(Trace.TRACE_TAG_VIEW, "deliverInputEvent",q.mEvent.getSequenceNumber());if (q.mReceiver != null) {boolean handled = (q.mFlags & QueuedInputEvent.FLAG_FINISHED_HANDLED) != 0;q.mReceiver.finishInputEvent(q.mEvent, handled);} else {q.mEvent.recycleIfNeededAfterDispatch();}recycleQueuedInputEvent(q);}

Input Pipeline的建立

Input Pipeline的建立，是在ViewRootImpl中的setView方法中，如下所示:

void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {......// 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;......
}

整个流水线的连接过程我们不再描述，最终建立起来了如下所示的流水线结构，流水从左向右进行执行，流水的起点由mFirstInputStage或者mFirstPostImeInputStage开始。

总结

本文描述了View处理input事件的Pipeline模型的实现，下一个章节讲述App处理input事件的具体过程。