1、概述

本文通过简单的实验法获取Android事件传递

2、测试代码

测试代码很简单，随便写一个按钮监听onTouch事件，在onTouch函数中抛出一个异常，代码如下：

      Button button = findViewById(R.id.btn_test);
      button.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View view, MotionEvent motionEvent) {
                Log.d(TAG," onTouch "+ motionEvent);
                throw new RuntimeException("event touch test");
//                return false;
            }
       });

3、测试结果：

结果当然崩了，不会写bug的程序员不是好程序员

2019-07-15 20:55:37.297 18471-18471/com.test.playground D/EventTestActivity:  onTouch MotionEvent { action=ACTION_DOWN, actionButton=0, id[0]=0, x[0]=118.0, y[0]=29.0, toolType[0]=TOOL_TYPE_FINGER, buttonState=0, metaState=0, flags=0x0, edgeFlags=0x0, pointerCount=1, historySize=0, eventTime=642618046, downTime=642618046, deviceId=9, source=0x1002 }
2019-07-15 20:55:37.300 18471-18471/com.test.playground E/InputEventReceiver: Exception dispatching input event.
2019-07-15 20:55:37.301 18471-18471/com.test.playground E/MessageQueue-JNI: Exception in MessageQueue callback: handleReceiveCallback
2019-07-15 20:55:37.302 18471-18471/com.test.playground E/MessageQueue-JNI: java.lang.RuntimeException: event touch test
        at com.test.playground.EventTestActivity$1.onTouch(EventTestActivity.java:23)
        at android.view.View.dispatchTouchEvent(View.java:10019)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2632)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2264)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2632)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2264)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2632)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2264)
        at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2632)
        at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2264)
        at com.android.internal.policy.DecorView.superDispatchTouchEvent(DecorView.java:414)
        at com.android.internal.policy.PhoneWindow.superDispatchTouchEvent(PhoneWindow.java:1808)
        at android.app.Activity.dispatchTouchEvent(Activity.java:3064)
        at com.android.internal.policy.DecorView.dispatchTouchEvent(DecorView.java:376)
        at android.view.View.dispatchPointerEvent(View.java:10243)
        at android.view.ViewRootImpl$ViewPostImeInputStage.processPointerEvent(ViewRootImpl.java:4438)
        at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:4306)
        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3853)
        at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3906)
        at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3872)
        at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3999)
        at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3880)
        at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:4056)
        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3853)
        at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3906)
        at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3872)
        at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3880)
        at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3853)
        at android.view.ViewRootImpl.deliverInputEvent(ViewRootImpl.java:6247)
        at android.view.ViewRootImpl.doProcessInputEvents(ViewRootImpl.java:6221)
        at android.view.ViewRootImpl.enqueueInputEvent(ViewRootImpl.java:6182)
        at android.view.ViewRootImpl$WindowInputEventReceiver.onInputEvent(ViewRootImpl.java:6350)
        at android.view.InputEventReceiver.dispatchInputEvent(InputEventReceiver.java:185)
        at android.os.MessageQueue.nativePollOnce(Native Method)
        at android.os.MessageQueue.next(MessageQueue.java:323)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:6121)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:889)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:779)
2019-07-15 20:55:37.303 18471-18471/com.test.playground D/AndroidRuntime: Shutting down VM

4 原理分析

4.1 事件从屏幕触摸到应用进程简述

触摸事件产生的大致原理是:用户对硬件进行操作(触摸屏)会导致这个硬件产生对应的中断。该硬件的驱动程序会处理这个中断。不同的硬件驱动程序处理的方式不同，不过最终都是将数据处理后存放进对应的/dev/input/eventX文件中。所以硬件驱动程序完成了触摸事件的数据收集。

在native层主要是通过下面3个组件来对触摸事件进行处理的，这3个组件都运行在系统服务中:

EventHub : 它的作用是监听、读取/dev/input目录下产生的新事件，并封装成RawEvent结构体供InputReader使用。
InputReader : 通过EventHub从/dev/input节点获取事件信息，转换成EventEntry事件加入到InputDispatcher的mInboundQueue队列中。
InputDispatcher : 从mInboundQueue队列取出事件，转换成DispatchEntry事件加入到Connection的outboundQueue队列。然后使用InputChannel分发事件到java层

4.2 应用进程中Touch系统框架原理

图1-Android事件传递类图

WindowInputEventReceiver: 在ViewRootImpl.setView中被初始化，当事件到来时会从native中回调onInputEvent方法到java层。是事件派发的动力所在。
ViewRootImpl: 处理视图方面的，同Input, Window等服务交互的大管家，会在Activity显示视图时初始化
InputStage: 被抽象成责任链模式的父类，代表着事件处理的阶段
View, ViewGroup, DecorView: 视图树的主要组成成分

从上面调用栈中可以得到下面调用的时序图：