View以及ViewGroup的事件处理流程
关于View的事件分发，这篇博客 讲的很清楚，大致总结下事件的流程
View.dispatchEvent->View.setOnTouchListener->View.onTouchEvent
在dispatchTouchEvent中会进行OnTouchListener的判断，如果这个view处于enable状态，OnTouchListener不为null且返回true，则表示事件被消费，onTouchEvent不会被执行；否则执行onTouchEvent。
在onTouchEvent中，如果return true就说明事件被消费了，当然如果这个View可以被点击（可以在代码中设置view.setonClickListener），或者长按(可以设置view.setonLongClickListener),也可以说明事件被消费
而他的后续博客也对ViewGroup的源码分析的很清楚，但是看了源码还是自己动手验证下嘛，因为我就写一写ViewGroup的事件的demo
package com.example.user.swipeview_01;
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.widget.LinearLayout;
/**
* Created by USER on 2015/9/30.
*/
public class MyLinearLayout extends LinearLayout {
private static final String TAG = "zhou";
public MyLinearLayout(Context context) {
super(context);
}
public MyLinearLayout(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyLinearLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
Log.d(TAG,"MyLinearLayout -> dispatchTouchEvent");
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
Log.d(TAG,"MyLinearLayout -> onInterceptTouchEvent");
return super.onInterceptTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
int action = event.getAction();
switch (action){
case MotionEvent.ACTION_DOWN:
Log.d(TAG,"MyLinearLayout -> onTouchEvent->ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG,"MyLinearLayout -> onTouchEvent->ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.d(TAG,"MyLinearLayout -> onTouchEvent->ACTION_UP");
break;
}
return super.onTouchEvent(event);
}
}
package com.example.user.swipeview_01;
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
/**
* Created by USER on 2015/9/30.
*/
public class MyView extends View {
private static final String TAG ="zhou";
public MyView(Context context) {
super(context);
}
public MyView(Context context, AttributeSet attrs) {
super(context, attrs);
}
public MyView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
Log.d(TAG,"MyView->dispatchTouchEvent");
return super.dispatchTouchEvent(event);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
int action = event.getAction();
switch(action){
case MotionEvent.ACTION_DOWN:
Log.d(TAG,"MyView->onTouchEvent->ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG,"MyView->onTouchEvent->ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.d(TAG,"MyView->onTouchEvent->ACTION_UP");
break;
}
return super.onTouchEvent(event);
}
}
布局
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent">
<com.example.user.swipeview_01.MyLinearLayout
android:background="#eeee5046"
android:layout_width="match_parent"
android:layout_height="match_parent">
<com.example.user.swipeview_01.MyView
android:background="#ee93ee74"
android:layout_width="300dp"
android:layout_height="200dp" />
</com.example.user.swipeview_01.MyLinearLayout>
</LinearLayout>
如果都不做事件的拦截的话
09-30 18:12:03.485 14514-14514/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
09-30 18:12:03.485 14514-14514/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onInterceptTouchEvent
09-30 18:12:03.486 14514-14514/com.example.user.swipeview_01 D/zhou﹕ MyView->dispatchTouchEvent
09-30 18:12:03.489 14514-14514/com.example.user.swipeview_01 D/zhou﹕ MyView->onTouchEvent->ACTION_DOWN
09-30 18:12:03.493 14514-14514/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_DOWN
ViewGroup(dispatchTouchEvent) -> ViewGroup(onInterceptTouchEvent)->Vie事件流程->ViewGroup(onTouchEvent)
为什么没有ACTION_MOVE 和 ACTION_UP事件，因为在ACTION_DOWN的时候，MyView不要，MyLinearLayout不要，事件就没有被消费，就没有找到target，所以后面就不用处理了
如果在MyView的onTouchEvent的最后返回的值为true的话
09-30 18:18:30.736 16701-16701/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
09-30 18:18:30.736 16701-16701/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onInterceptTouchEvent
09-30 18:18:30.737 16701-16701/com.example.user.swipeview_01 D/zhou﹕ MyView->dispatchTouchEvent
09-30 18:18:30.741 16701-16701/com.example.user.swipeview_01 D/zhou﹕ MyView->onTouchEvent->ACTION_DOWN
09-30 18:18:30.764 16701-16701/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
09-30 18:18:30.764 16701-16701/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onInterceptTouchEvent
09-30 18:18:30.765 16701-16701/com.example.user.swipeview_01 D/zhou﹕ MyView->dispatchTouchEvent
09-30 18:18:30.765 16701-16701/com.example.user.swipeview_01 D/zhou﹕ MyView->onTouchEvent->ACTION_MOVE
09-30 18:18:30.784 16701-16701/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
09-30 18:18:30.784 16701-16701/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onInterceptTouchEvent
09-30 18:18:30.784 16701-16701/com.example.user.swipeview_01 D/zhou﹕ MyView->dispatchTouchEvent
09-30 18:18:30.785 16701-16701/com.example.user.swipeview_01 D/zhou﹕ MyView->onTouchEvent->ACTION_MOVE
09-30 18:18:30.793 16701-16701/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
09-30 18:18:30.793 16701-16701/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onInterceptTouchEvent
09-30 18:18:30.793 16701-16701/com.example.user.swipeview_01 D/zhou﹕ MyView->dispatchTouchEvent
09-30 18:18:30.796 16701-16701/com.example.user.swipeview_01 D/zhou﹕ MyView->onTouchEvent->ACTION_UP
可以看到在MyView的onTouchEvent的ACTION_DOWN中消费了事件，MyLinearLayout的onTouchEvent就不能处理ACTION_DOWN了，既然找到了target为MyView,那么事件每次都要继续往下传递，然后的ACTION_MOVE和ACTION_UP都会最终到MyView处理了，不再到MyLinearLayout中的onTouchEvent了
如果在MyView的onTouchEvent返回true，再把MyLinearLayout中的onIntercetptTouchEvent返回true ,也就是说MyLinearLayout要截断这个事件不让事件往下传到MyView
10-08 09:52:19.038 5891-5891/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 09:52:19.039 5891-5891/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onInterceptTouchEvent
10-08 09:52:19.041 5891-5891/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_DOWN
10-08 09:52:20.009 5891-5891/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 09:52:20.009 5891-5891/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onInterceptTouchEvent
10-08 09:52:20.011 5891-5891/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_DOWN
10-08 09:52:20.698 5891-5891/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 09:52:20.699 5891-5891/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onInterceptTouchEvent
10-08 09:52:20.702 5891-5891/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_DOWN
10-08 09:52:21.544 5891-5891/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 09:52:21.544 5891-5891/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onInterceptTouchEvent
10-08 09:52:21.546 5891-5891/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_DOWN
10-08 09:54:51.304 5891-5891/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 09:54:51.305 5891-5891/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onInterceptTouchEvent
10-08 09:54:51.307 5891-5891/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_DOWN
我们可以看到，事件已经不在传递到MyView，只会传递到MyLinearLayout的onTouchEvent中，但是也只是处理ACTION_DOWN，这又是怎么回事呢，因为在MyLinearLayout中的onTouchEvent，我们没有对事件进行消费，也就是说没有return true，而是把事件交给了父View处理，也就是super.onTouchEvent。
既然这样，我们再把MyLinearlayout中的onTouchEvent返回true试试
10-08 09:58:18.037 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 09:58:18.037 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onInterceptTouchEvent
10-08 09:58:18.040 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_DOWN
10-08 09:58:18.054 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 09:58:18.056 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_MOVE
10-08 09:58:18.071 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 09:58:18.071 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_MOVE
10-08 09:58:18.091 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 09:58:18.091 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_MOVE
10-08 09:58:18.108 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 09:58:18.109 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_MOVE
10-08 09:58:18.127 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 09:58:18.127 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_MOVE
10-08 09:58:18.147 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 09:58:18.148 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_MOVE
10-08 09:58:18.164 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 09:58:18.165 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_MOVE
10-08 09:58:18.184 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 09:58:18.184 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_MOVE
10-08 09:58:18.195 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 09:58:18.195 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_MOVE
10-08 09:58:18.204 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 09:58:18.207 7250-7250/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_UP
OK,如我们之前所说，既然onInterceptTouchEvent方法，截断了事件往下传递，那么自己就应该处理事件，在ACTION_DOWN事件中，正好我们现在在MyLinearLayout中的onTouchEvent方法中返回了true(自己处理)，所以就找到了target来处理后面的事件，上面 的Log信息正是这样。
现在总结 下，关键在哪里呢，target! 也就是ACTION_DOWN事件找的target，如果在ACTION_DOWN的时候没有找到target，那么 走系统的流程，如果找到了后续所有事件都由这个target处理。 好，我们来验证我们的结论
在MyLinearLayout中
@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
Log.d(TAG,"MyLinearLayout -> onInterceptTouchEvent");
return super.onInterceptTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
int action = event.getAction();
switch (action){
case MotionEvent.ACTION_DOWN:
Log.d(TAG,"MyLinearLayout -> onTouchEvent->ACTION_DOWN");
return true;
case MotionEvent.ACTION_MOVE:
Log.d(TAG,"MyLinearLayout -> onTouchEvent->ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.d(TAG,"MyLinearLayout -> onTouchEvent->ACTION_UP");
break;
}
return super.onTouchEvent(event);
}
没有截断事件，只在ACTION_DOWN事件中返回true，也就是说如果target为MyLinearLayout，后续事件都由MyLinearLayout来处理
在MyView中
@Override
public boolean onTouchEvent(MotionEvent event) {
int action = event.getAction();
switch(action){
case MotionEvent.ACTION_DOWN:
Log.d(TAG,"MyView->onTouchEvent->ACTION_DOWN");
return super.onTouchEvent(event);
//break;
case MotionEvent.ACTION_MOVE:
Log.d(TAG,"MyView->onTouchEvent->ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.d(TAG,"MyView->onTouchEvent->ACTION_UP");
break;
}
//return super.onTouchEvent(event);
return true;
}
我们在ACTION_DOWN事件中，没有返回true，在其它事件中返回了true，也就是说我们不让target为MyView，所以后续就算ACTION_MOVE , ACTION_UP返回true，也不会到这里处理
看下Log信息
10-08 10:06:23.156 9343-9343/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 10:06:23.157 9343-9343/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onInterceptTouchEvent
10-08 10:06:23.157 9343-9343/com.example.user.swipeview_01 D/zhou﹕ MyView->dispatchTouchEvent
10-08 10:06:23.162 9343-9343/com.example.user.swipeview_01 D/zhou﹕ MyView->onTouchEvent->ACTION_DOWN
10-08 10:06:23.164 9343-9343/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_DOWN
10-08 10:06:23.178 9343-9343/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 10:06:23.179 9343-9343/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_MOVE
10-08 10:06:23.199 9343-9343/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 10:06:23.200 9343-9343/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_MOVE
10-08 10:06:23.218 9343-9343/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 10:06:23.218 9343-9343/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_MOVE
10-08 10:06:23.229 9343-9343/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 10:06:23.229 9343-9343/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_MOVE
10-08 10:06:23.236 9343-9343/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> dispatchTouchEvent
10-08 10:06:23.239 9343-9343/com.example.user.swipeview_01 D/zhou﹕ MyLinearLayout -> onTouchEvent->ACTION_UP
很好，正如我们所料，在ACTION_DOWN时候走了系统的流程，dispatchTouchEvent(
MyLinearLayout
) -> onInterceptTouchEvent(MyLinearLayout ) ->
dispatchTouchEvent(MyView
) -> onTouchEvent(MyView)：ACTION_DOWN
但是MyView的onTouchEvent并没有返回true，自然转到了MyLinearLayout中的onTouchEvent了，而此时ACTION_DOWN返回了true，也就是说MyLinearLayout作为 了这个事件的target，就算MyLinearLayout的ACTION_MOVE，ACTION_UP走的是系统流程，照样进行事件处理，为什么，因为劳资就是target，不给我处理，给谁处理~
画个草图看下事件如何找到target的，只要target找到以后都由这个target来处理事件，除非有特殊情况 ，例如子View，getParent().requestDisallowInterceptTouchEvent(true)不允许父View截断事件，当然这是后话
当我们找到target以后 ，其它的View的onTouchEvent必然不会再处理事件了，后续我会用一些demo来验证这些理论。
读源码有时候并不容易 ，但是既然有人已经 做过这些事情，我就不做了，因为我不需要去写源码 ，我只需要知道这个东西如何用就行，当然如果你够强大 ，就从源码学习吧~