Android7 Input（九）View 建立Input Pipeline

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。