标签：事件分发机制
转载请注明出处：http://blog.csdn.net/chziroy/article/details/44401615
要理解Android事件分发机制，首先得了解几个概念，也算是总结，如果暂时看不懂也无妨，本文会讲解这几个问题。
1，点击屏幕，首先事件的传递从Activity的dispatchTouchEvent()方法开始。
2，关于Android事件分发机制，相关方法的方法有三个：onTouchEvent()，dispatchTouchEvent()，还有onInterceptTouchEvent()，而相关的类有Activity，View，ViewGroup。
3，时间的分发顺序为dispatchTouchEvent --- onInterceptTouchEvent --- onTouchEvent
4，Android事件分发机制，有一个向下分发过程，该过程主要调用dispatchTouchEvent，还有一个向上返回过程，主要依靠onTouchEvent方法，
5，Android事件从父视图分发到子视图，如果事件被拦截，则事件不会继续向下分发，而被当前视图消耗。此时上述的向下分发过程提前结束
6，没有被消耗的事件，从父视图逐级分发到子视图，最后又回到Activity，被Activity中的onTouchEvent()消耗。此时上述的向上返回过程提前结束
本文不会直接贴出上述相关方法和类的源代码，而会贴出其“伪代码”，方便理解。
先从事件分发的起点开始，也就是Activity的dispatchTouchEvent()方法，
public boolean dispatchTouchEvent(MotionEvent ev) {
//第一步，将事件分发
//第二步，如果事件在分发中没被消耗，则传递给Activity的onTouchEvent()方法
}
上述代码的第一步“将事件分发”，那事件会分发到哪里呢，分发到它的根布局的一个ViewGroup（其实就算你的activity的布局文件没有设置一个LinearLayout这样的根布局，系统也会默认给你加一个默认的FrameLayout）。事件分发到了ViewGroup中，就进入了ViewGroup的dispatchTouchEvent 方法，在查看该方法的源码时，Android3.0之前该方法的源码和更高版本中的源码是不同的。不过原理大致相同。以下是该方法的原理。
public boolean dispatchTouchEvent(MotionEvent ev) {
调用onInterceptTouchEvent检查是否拦截事件
if(没有拦截){
在ViewGroup中遍历查找目前是点击了哪个子视图
if(找到了){
调用该子视图的dispatchTouchEvent，递归下去
}else{
没找到，则将事件传给onTouchListener，没有Listener则传给onTouchEvent()
如果再listener或者onTouchEvent()中down事件返回了true，代表事件被消费，后续的move和up都被Listener或者onTouchEvent()处理，
如果down事件返回false，则后续的move，up事件将不会到这一层的Viewgroup，而直接在上一层视图被消费。
}
}else{
事件被拦截了，原本被点击的子视图将接收到一个ACTION_CANCEL事件，而down事件传给onTouchListener，没有Listener则传给onTouchEvent()，依然遵从上面的down和move,up事件的关系
}
} public boolean dispatchTouchEvent(MotionEvent ev) {
//如果有listener，则把事件传递给listener
//如果没有listener，则把事件传递给onTouchEvent()
} /**
* Implement this method to intercept all touch screen motion events. This
* allows you to watch events as they are dispatched to your children, and
* take ownership of the current gesture at any point.
*
* <p>Using this function takes some care, as it has a fairly complicated
* interaction with {@link View#onTouchEvent(MotionEvent)
* View.onTouchEvent(MotionEvent)}, and using it requires implementing
* that method as well as this one in the correct way. Events will be
* received in the following order:
*
* <ol>
* <li> You will receive the down event here.
* <li> The down event will be handled either by a child of this view
* group, or given to your own onTouchEvent() method to handle; this means
* you should implement onTouchEvent() to return true, so you will
* continue to see the rest of the gesture (instead of looking for
* a parent view to handle it). Also, by returning true from
* onTouchEvent(), you will not receive any following
* events in onInterceptTouchEvent() and all touch processing must
* happen in onTouchEvent() like normal.
* <li> For as long as you return false from this function, each following
* event (up to and including the final up) will be delivered first here
* and then to the target's onTouchEvent().
* <li> If you return true from here, you will not receive any
* following events: the target view will receive the same event but
* with the action {@link MotionEvent#ACTION_CANCEL}, and all further
* events will be delivered to your onTouchEvent() method and no longer
* appear here.
* </ol>
*
* @param ev The motion event being dispatched down the hierarchy.
* @return Return true to steal motion events from the children and have
* them dispatched to this ViewGroup through onTouchEvent().
* The current target will receive an ACTION_CANCEL event, and no further
* messages will be delivered here.
*/
public boolean onInterceptTouchEvent(MotionEvent ev) {
return false;
}
一言以蔽之：也就是“两个过程，两个截断”
参考过的几篇比较优秀的博客
http://codetheory.in/understanding-android-input-touch-events/
http://www.cnblogs.com/sunzn/archive/2013/05/10/3064129.html#top
https://gist.github.com/Leaking/16e682b1ffac3a59c3df
标签：事件分发机制
原文地址：http://blog.csdn.net/chziroy/article/details/44401615
