Android7 Input（十）View 处理Input事件pipeline

概述:

        本文主要描述View对InputEvent事件pipeline处理过程。

本文涉及的源码路径

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

InputEvent事件处理

View处理input事件是调用doProcessInputEvents方法，如下所示:

 void doProcessInputEvents() {// Deliver all pending input events in the queue.while (mPendingInputEventHead != null) {QueuedInputEvent q = mPendingInputEventHead;/* 更新事件处理的位置 */mPendingInputEventHead = q.mNext;/* 处理到了队列的尾部 */if (mPendingInputEventHead == null) {mPendingInputEventTail = null;}q.mNext = null;......deliverInputEvent(q);}......}

该方法的核心实现逻辑如下:

1、从事件队列中取出一个待处理的Input事件;

2、调用deliverInputEvent()进行处理；

3、处理完所有事件后，退出循环体;

我们继续讲解deliverInputEvent方法，实现如下:

 private void deliverInputEvent(QueuedInputEvent q) {......InputStage stage;if (q.shouldSendToSynthesizer()) {stage = mSyntheticInputStage;} else {stage = q.shouldSkipIme() ? mFirstPostImeInputStage : mFirstInputStage;}/* 开启事件分发 */if (stage != null) {stage.deliver(q);} else {finishInputEvent(q);}}

该方法，根据事件q设置的flag，从InputStage Pipeline的不同起点，开始处理input事件，为了简化叙述，我们从点击触摸屏输入事件的处理讲起。我跳过输入法相关，流水线的处理起点为mFirstPostImeInputStage，也就是earlyPostImeStage。

InputEvent事件处理Pipeline

承接上文，我们开始将入inputEvent事件的处理Pipeline,前面的文章我们已经讲述了InputStage的处理模型，因此不再详解讲述每一个pipeline被调用到的过程，我们只讲述每一级中核心方法onProcess。 为了简化讲述的过程，我们跳过与输入法相关的，流水线起点为earlyPostImeStage

1、EarlyPostImeStage

调用EarlyPostImeInputStage类中的process方法，如下所示:

 protected int onProcess(QueuedInputEvent q) {if (q.mEvent instanceof KeyEvent) {return processKeyEvent(q);} else {final int source = q.mEvent.getSource();if ((source & InputDevice.SOURCE_CLASS_POINTER) != 0) {return processPointerEvent(q);}}return FORWARD;}

我们只关注触摸事件，因此直接调用processPointerEvent()进行处理，这部分代码不再展开详细描述，当EarlyPostImeInputStage处理完inputEvent后，返回FORWARD，表示将该inputEvent事件传递给下一级的流水线进行处理，也就是NativePostImeInputStage处理。

2、NativePostImeInputStage

调用NativePostImeInputStage中的onProcess方法，如下所示:

protected int onProcess(QueuedInputEvent q) {if (mInputQueue != null && q.mEvent instanceof KeyEvent) {mInputQueue.sendInputEvent(q.mEvent, q, true, this);return DEFER;}return FORWARD;}

该方法只处理按键事件，其他事件直接转发，事件传递给下一级的流水线进行处理，也就是ViewPostImeInputStage

3、ViewPostImeInputStage

调用ViewPostImeInputStage中的onProcess方法，如下所示:

 protected int onProcess(QueuedInputEvent q) {if (q.mEvent instanceof KeyEvent) {return processKeyEvent(q);} else {final int source = q.mEvent.getSource();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);}}}

我们只关注触摸事件，直接调用processPointerEvent进行处理，如下所示:

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;}

该方法的核心逻辑如下:

1、找到传递事件的Viw视图入口。这里事件在Android UI窗口处理的起点是Activity。我们下一章进行讲解，这里先暂时跳过；

2、根据处理结果，如果事件被处理了，返回FINISH_HANDLED,不再向下一级的流水线传递，如果没有处理，则直接转发到下一级的流水线处理，也就是SyntheticInputStage，为了简化叙述，我们这里假设input事件被处理了，则apply的对返回结果的处理如下所示:

 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);}}

由于事件已经被处理，所以直接调用finish，如下所示:

 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);}

finish中标记inputEvent事件被处理标记，然后再次调用forward，最终调用到了onDeliverToNext接口，如下所示:

 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);}}

最终调用的是SyntheticInputStage中onDeliverToNext方法，如下所示:

protected void onDeliverToNext(QueuedInputEvent q) {......super.onDeliverToNext(q);}

然后有调用到了父类的onDeliverToNext，也就是InputStage中的onDeliverToNext方法，此时流水线已经到达了末端，然后进入到finishInputEvent方法如下所示:

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);}

核心逻辑就是调用finishInputEvent进行收尾工作，方法如下所示:

 public final void finishInputEvent(InputEvent event, boolean handled) {......} else {int index = mSeqMap.indexOfKey(event.getSequenceNumber());if (index < 0) {Log.w(TAG, "Attempted to finish an input event that is not in progress.");} else {int seq = mSeqMap.valueAt(index);mSeqMap.removeAt(index);nativeFinishInputEvent(mReceiverPtr, seq, handled);}}event.recycleIfNeededAfterDispatch();}

核心就是调用JNI层中的nativeFinishInputEvent方法,如下所示:

static void nativeFinishInputEvent(JNIEnv* env, jclass clazz, jlong receiverPtr,jint seq, jboolean handled) {sp<NativeInputEventReceiver> receiver =reinterpret_cast<NativeInputEventReceiver*>(receiverPtr);status_t status = receiver->finishInputEvent(seq, handled);if (status && status != DEAD_OBJECT) {String8 message;message.appendFormat("Failed to finish input event.  status=%d", status);jniThrowRuntimeException(env, message.string());}
}

继续调用finishInputEvent方法，我们进一步追踪，最终调用到了sendUnchainedFinishedSignal这个方法，如下所示:

status_t InputConsumer::sendUnchainedFinishedSignal(uint32_t seq, bool handled) {InputMessage msg;msg.header.type = InputMessage::TYPE_FINISHED;msg.body.finished.seq = seq;msg.body.finished.handled = handled;return mChannel->sendMessage(&msg);
}

        这里又看到了熟悉的InputChannel的东西，最后将结束处理的信息通过夸进程通知到了InputDispatcher；然后触发epoll事件，调用到handleReceiveCallback方法进行处理完事件的清理工作，这里不再展开描述;

总结

        本文描述了Android系统中View对输入事件的处理流程，也就是pipeline事件的处理过程。然后最终将处理结果通过跨进程传递给了InputDispatcher。下一章，我们讲述View UI的事件分发流程；