继续分析DrawerLayout的手势分发部分

谈到手势分发，这本身就是个好话题，DrawerLayout作为继承自ViewGroup得布局他可以拦截手势也可以分发给子view，也就是在onInterceptTouchEvent中做的操作，但是他的下面还有一个onTouchEvent方法，先看哪个呢？追溯代码我们可以知道ViewGroup继承自View，而onTouchEvent是View的方法

file:///D:/Program/WizNote/temp/d1498a17-8f4e-4bea-8106-a660021ba2ce_4_files/27be3305-09a6-4382-9539-2f718ca05908.png

我们还是先花点时间把两者的关系先确认再继续。

onInterceptTouchEvent和onTouchEvent---鸡和蛋？

定位到ViewGroup，可以发现onInterceptTouchEvent分定义如下，从它前面一段非常长的注释就可以看出其重要性和复杂，默认的返回是false

/**

* 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;

}

好不错不错