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; }
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