ViewGroup事件传递

ViewGroup事件传递
    同一事件序列指从手指接触屏幕到手指离开屏幕

    MotionEvent ---> Activity ---> Window ---> DecorView
    获取方法Activity.getWindow().getDecorView()

    Activity#dispatchTouchEvent

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        public boolean dispatchTouchEvent(MotionEvent ev){

            ......

            if(getWindow().superDispatchTouchEvent(ev)){
                return true;
            }
            return onTouchEvent(ev);
        }

        Activity调用附属的Window分发 false---> 没人处理，调用Activity自身onTouchEvent

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    PhoneWindow#superDispatchTouchEvent

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        public boolean superDispatchTouchEvent(MotionEvent event){
            return mDecor.superDispatchTouchEvent(event);
        }

        Window唯一实现类PhoneWindow
        PhoneWindow将事件传递给DecorView

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    DecorView

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        ((ViewGroup)getWindow().getDecorView().findViewById(android.R.id.content)).getChildAt(0);
        获取我们通过setContentView设置的View

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    ViewGroup#dispatchTouchEvent

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        // 拦截状态
        final boolean intercepted;
        if(actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null){
            final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT)!=0;
            if(!disallowIntercept){
                intercepted = onInterceptTouchEvent(ev);
                ev.setAction(action);
            }else{
                intercepted = false;
            }
        } else {
            intercepted = true;
        }

        说明：
            dispatchTouchEvent $ ACTION_DOWN --> onInterceptTouchEvent()
            dispatchTouchEvent $ ACTION_MOVE ACTION_UP --> ACTION_DOWN事件中当前ViewGroup不拦截 --> onInterceptTouchEvent()
            1、ACTION_DOWN --> onInterceptTouchEvent(ev) --> intercepted==true 当前ViewGroup拦截 --> mFirstTouchTarget==null
               --> ACTION_MOVE、ACTION_UP --> 由于条件不成立，导致无法再调用onInterceptTouchEvent()
            2、mFirstTouchTarget有子元素成功处理事件被赋值

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        ACTION_DOWN
            ACTION_DOWN时始终是如下值：
            处理事件的子View mFirstTouchTarget==null  还未有子View处理事件，肯定为null
            子View请求拦截 disallowIntercept=false    ACTION_DOWN事件时会重置该值，所以肯定是false

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       ViewGroup#onInterceptTouchEvent()

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            intercepted==false当前ViewGroup不拦截           intercepted==true当前ViewGroup拦截
            mFirstTouchTarget != null                      mFirstTouchTarget==null

            ACTION_MOVE                                    ACTION_MOVE

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            disallowIntercept==true                        onInterceptTouchEvent()方法不再调用，直接调用当前ViewGroup的onTouchEvent()
            请求不拦截 --> 调用子View相关方法
            disallowIntercept==false
            请求拦截 --> onInterceptTouchEvent() --> intercepted

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       不拦截事件时分发给子View


    总结： 1、ACTION_DOWN事件时，如果拦截了，那么不再调用onInterceptTouchEvent()
          2、子View设置的请求是否拦截，只有在非ACTION_DOWN事件时生效


View点击事件的处理
    这里没有事件拦截，在dispatchTouchEvent()中判断是否设置OnTouchListener
    OnTouchListener#onTouch
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    false onTouchEvent       true onTouchEvent不再调用

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    设置了OnClickListener则调用