Android View 事件分发机制 源码解析 （上）

布局文件：

<LinearLayout xmlns:android=“http://schemas.android.com/apk/res/android”

xmlns:tools=“http://schemas.android.com/tools”

android:layout_width=“match_parent”

android:layout_height=“match_parent”

tools:context=“.MainActivity” >

<com.example.zhy_event03.MyButton

android:id=“@+id/id_btn”

android:layout_width=“wrap_content”

android:layout_height=“wrap_content”

android:text=“click me” />

最后看一眼MainActivity的代码

package com.example.zhy_event03;

import android.app.Activity;

import android.os.Bundle;

import android.util.Log;

import android.view.MotionEvent;

import android.view.View;

import android.view.View.OnTouchListener;

import android.widget.Button;

public class MainActivity extends Activity

{

protected static final String TAG = “MyButton”;

private Button mButton ;

@Override

protected void onCreate(Bundle savedInstanceState)

{

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

mButton = (Button) findViewById(R.id.id_btn);

mButton.setOnTouchListener(new OnTouchListener()

{

@Override

public boolean onTouch(View v, MotionEvent event)

{

int action = event.getAction();

switch (action)

{

case MotionEvent.ACTION_DOWN:

Log.e(TAG, “onTouch ACTION_DOWN”);

break;

case MotionEvent.ACTION_MOVE:

Log.e(TAG, “onTouch ACTION_MOVE”);

break;

case MotionEvent.ACTION_UP:

Log.e(TAG, “onTouch ACTION_UP”);

break;

default:

break;

}

return false;

}

});

}

}

在MainActivity中，我们还给MyButton设置了OnTouchListener这个监听~

好了，跟View事件相关一般就这三个地方了，一个onTouchEvent，一个dispatchTouchEvent，一个setOnTouchListener;

下面我们运行，然后点击按钮，查看日志输出：

08-31 06:09:39.030: E/MyButton(879): dispatchTouchEvent ACTION_DOWN

08-31 06:09:39.030: E/MyButton(879): onTouch ACTION_DOWN

08-31 06:09:39.049: E/MyButton(879): onTouchEvent ACTION_DOWN

08-31 06:09:39.138: E/MyButton(879): dispatchTouchEvent ACTION_MOVE

08-31 06:09:39.138: E/MyButton(879): onTouch ACTION_MOVE

08-31 06:09:39.147: E/MyButton(879): onTouchEvent ACTION_MOVE

08-31 06:09:39.232: E/MyButton(879): dispatchTouchEvent ACTION_UP

08-31 06:09:39.248: E/MyButton(879): onTouch ACTION_UP

08-31 06:09:39.248: E/MyButton(879): onTouchEvent ACTION_UP

我有意点击的时候蹭了一下，不然不会触发MOVE，手抖可能会打印一堆MOVE的日志~~~

好了，可以看到，不管是DOWN，MOVE，UP都会按照下面的顺序执行：

1、dispatchTouchEvent

2、 setOnTouchListener的onTouch

3、onTouchEvent

下面就跟随日志的脚步开始源码的探索~

2、dispatchTouchEvent

====================

首先进入View的dispatchTouchEvent

/**

• Pass the touch screen motion event down to the target view, or this

• view if it is the target.

• @param event The motion event to be dispatched.

• @return True if the event was