Android事件分發機制簡單理解

caremmm發表於2020-11-08
Android事件

參考連結https://blog.csdn.net/caifengyao/article/details/65437695?utm_medium=distribute.pc_relevant_t0.none-task-blog-BlogCommendFromMachineLearnPai2-1.channel_param&depth_1-utm_source=distribute.pc_relevant_t0.none-task-blog-BlogCommendFromMachineLearnPai2-1.channel_param 

View只能處理事件，不能往下分發事件。ViewGroup要先分發事件，再處理事件。

 

ViewGroup中

事件分為 dispatchTouchEvent（事件的分發），onInterceptTouchEvent（事件的攔截，返回true 代表攔截事件），onTouchEvent（事件的處理，返回true代表消費事件）

View中

事件分為dispatchTouchEvent（事件的分發），onTouchEvent（事件的處理）。

事件分發的順序

Activity -> ViewGroup -> View。

從上層往下層分發(ViewGroup 即為上層，View 為下層)，從下層往上層處理。

例子

class MyViewGroup(context: Context, attributeSet: AttributeSet): LinearLayout(context, attributeSet){
    override fun dispatchTouchEvent(event: MotionEvent?): Boolean {
        when (event?.action) {
            MotionEvent.ACTION_DOWN -> {
                Log.d("MyView.class", "ViewGroup_dispacth_DOWN")
            }
            MotionEvent.ACTION_MOVE -> {
                Log.d("MyView.class", "ViewGroup_dispacth_MOVE")
            }
            MotionEvent.ACTION_UP -> {
                Log.d("MyView.class", "ViewGroup_dispacth_UP")
            }
        }
        return super.dispatchTouchEvent(event)
    }

    override fun onInterceptTouchEvent(ev: MotionEvent?): Boolean {
        when (ev?.action) {
            MotionEvent.ACTION_DOWN -> {
                Log.d("MyView.class", "ViewGroup_intercept_DOWN")
            }
            MotionEvent.ACTION_MOVE -> {
                Log.d("MyView.class", "ViewGroup_intercept_MOVE")
            }
            MotionEvent.ACTION_UP -> {
                Log.d("MyView.class", "ViewGroup_intercept_UP")
            }
        }
        return super.onInterceptTouchEvent(ev)
    }

    override fun onTouchEvent(event: MotionEvent?): Boolean {
        when (event?.action) {
            MotionEvent.ACTION_DOWN -> {
                Log.d("MyView.class", "ViewGroup_onTouch_DOWN")
            }
            MotionEvent.ACTION_MOVE -> {
                Log.d("MyView.class", "ViewGroup_onTouch_MOVE")
            }
            MotionEvent.ACTION_UP -> {
                Log.d("MyView.class", "ViewGroup_onTouch_UP")
            }
        }
        return super.onTouchEvent(event)
    }
}
class MyView(context: Context, attributeSet: AttributeSet): View(context, attributeSet){
    override fun dispatchTouchEvent(event: MotionEvent?): Boolean {
        when (event?.action) {
            MotionEvent.ACTION_DOWN -> {
                Log.d("MyView.class", "View_dispacth_DOWN")
            }
            MotionEvent.ACTION_MOVE -> {
                Log.d("MyView.class", "View_dispacth_MOVE")
            }
            MotionEvent.ACTION_UP -> {
                Log.d("MyView.class", "View_dispacth_UP")
            }
        }
        return super.dispatchTouchEvent(event)
    }

    override fun onTouchEvent(event: MotionEvent?): Boolean {
        when (event?.action) {
            MotionEvent.ACTION_DOWN -> {
                Log.d("MyView.class", "View_onTouch_DOWN")
            }
            MotionEvent.ACTION_MOVE -> {
                Log.d("MyView.class", "View_onTouch_MOVE")
            }
            MotionEvent.ACTION_UP -> {
                Log.d("MyView.class", "View_onTouch_UP")
            }
        }
        return super.onTouchEvent(event)
    }
}

 

產生以下流程的事件均為點選custom_view

1. 對以上方法均不作處理，都返回super(呼叫父類方法，返回預設值)。這意味著我們既不攔截，也不消費。

 

2020-11-04 20:07:12.492 28679-28679/com.cl.eventtest D/MyView.class: Activity_dispatch_DOWN
2020-11-04 20:07:12.493 28679-28679/com.cl.eventtest D/MyView.class: ViewGroup_dispacth_DOWN
2020-11-04 20:07:12.493 28679-28679/com.cl.eventtest D/MyView.class: ViewGroup_intercept_DOWN
2020-11-04 20:07:12.493 28679-28679/com.cl.eventtest D/MyView.class: View_dispacth_DOWN
2020-11-04 20:07:12.495 28679-28679/com.cl.eventtest D/MyView.class: View_onTouch_DOWN
2020-11-04 20:07:12.496 28679-28679/com.cl.eventtest D/MyView.class: ViewGroup_onTouch_DOWN
2020-11-04 20:07:12.497 28679-28679/com.cl.eventtest D/MyView.class: Activity_onTouch_DOWN
2020-11-04 20:07:12.501 28679-28679/com.cl.eventtest D/MyView.class: Activity_dispatch_MOVE
2020-11-04 20:07:12.501 28679-28679/com.cl.eventtest D/MyView.class: Activity_onTouch_MOVE
2020-11-04 20:07:12.528 28679-28679/com.cl.eventtest D/MyView.class: Activity_dispatch_MOVE
2020-11-04 20:07:12.528 28679-28679/com.cl.eventtest D/MyView.class: Activity_onTouch_MOVE
2020-11-04 20:07:12.529 28679-28679/com.cl.eventtest D/MyView.class: Activity_dispatch_UP
2020-11-04 20:07:12.529 28679-28679/com.cl.eventtest D/MyView.class: Activity_onTouch_UP

 

 

如果對事件既不攔截，也不消費，當觸發ACTION_DOWN的時候，事件會經過Activity——ViewGroup——View一層層的向下進行dispatchTouchEvent（分發）—onInterceptTouchEvent（攔截）呼叫。當到達最底層View後，開始觸發消費操作，因為均不消費，ACTION_DOWN將由底層一層層向上冒，移交上層處理。當抵達最上層Activity後，說明下層均不消費，之後觸發的ACTION_MOVE和ACTION_UP將不再向下層分發傳遞，直接交由Activity分發給自己進行處理。

 

2.將VIewGroup的onInterceptTouchEvent返回值改為true，即意味著ViewGroup攔截事件，但是並沒有消費。

 

2020-11-04 20:14:33.591 3187-3187/com.cl.eventtest D/MyView.class: Activity_dispatch_DOWN
2020-11-04 20:14:33.592 3187-3187/com.cl.eventtest D/MyView.class: ViewGroup_dispacth_DOWN
2020-11-04 20:14:33.592 3187-3187/com.cl.eventtest D/MyView.class: ViewGroup_intercept_DOWN
2020-11-04 20:14:33.592 3187-3187/com.cl.eventtest D/MyView.class: ViewGroup_onTouch_DOWN
2020-11-04 20:14:33.593 3187-3187/com.cl.eventtest D/MyView.class: Activity_onTouch_DOWN
2020-11-04 20:14:33.622 3187-3187/com.cl.eventtest D/MyView.class: Activity_dispatch_MOVE
2020-11-04 20:14:33.622 3187-3187/com.cl.eventtest D/MyView.class: Activity_onTouch_MOVE
2020-11-04 20:14:33.630 3187-3187/com.cl.eventtest D/MyView.class: Activity_dispatch_UP
2020-11-04 20:14:33.630 3187-3187/com.cl.eventtest D/MyView.class: Activity_onTouch_UP

只是攔截事件，但是沒有消費事件，那麼 dispatchTouchEvent 不會繼續往下呼叫，但是 onTouchEvent（）還是會一層層往上呼叫。

3. ViewGroup的 onInterceptTouchEvent() 仍然返回super.onInterceptTouchEvent()，但是 onTouchEvent() 返回 true。即表示ViewGroup不攔截事件，但是消費事件。

2020-11-04 20:22:49.363 4290-4290/com.cl.eventtest D/MyView.class: Activity_dispatch_DOWN
2020-11-04 20:22:49.364 4290-4290/com.cl.eventtest D/MyView.class: ViewGroup_dispacth_DOWN
2020-11-04 20:22:49.364 4290-4290/com.cl.eventtest D/MyView.class: ViewGroup_intercept_DOWN
2020-11-04 20:22:49.364 4290-4290/com.cl.eventtest D/MyView.class: View_dispacth_DOWN
2020-11-04 20:22:49.365 4290-4290/com.cl.eventtest D/MyView.class: View_onTouch_DOWN
2020-11-04 20:22:49.366 4290-4290/com.cl.eventtest D/MyView.class: ViewGroup_onTouch_DOWN
2020-11-04 20:22:49.367 4290-4290/com.cl.eventtest D/MyView.class: Activity_dispatch_MOVE
2020-11-04 20:22:49.367 4290-4290/com.cl.eventtest D/MyView.class: ViewGroup_dispacth_MOVE
2020-11-04 20:22:49.367 4290-4290/com.cl.eventtest D/MyView.class: ViewGroup_onTouch_MOVE
2020-11-04 20:22:49.368 4290-4290/com.cl.eventtest D/MyView.class: Activity_dispatch_UP
2020-11-04 20:22:49.368 4290-4290/com.cl.eventtest D/MyView.class: ViewGroup_dispacth_UP
2020-11-04 20:22:49.368 4290-4290/com.cl.eventtest D/MyView.class: ViewGroup_onTouch_UP

 

此時因為沒有攔截事件，Down事件仍然會下發到View ，但是事件在 ViewGroup 中消費了，所以不會向上傳遞給 Activity 處理。

同時之後的 MOVE 以及 UP 事件都不會向下分發到 View ，因為已經知道DOWN事件被ViewGroup消費了。

 

4. ViewGroup的 onInterceptTouchEvent() 和onTouchEvent() 的返回值均改為true，則意味著ViewGroup既攔截了事件，同時也消費了事件。

 

2020-11-04 20:31:00.920 6527-6527/com.cl.eventtest D/MyView.class: Activity_dispatch_DOWN
2020-11-04 20:31:00.925 6527-6527/com.cl.eventtest D/MyView.class: ViewGroup_dispacth_DOWN
2020-11-04 20:31:00.925 6527-6527/com.cl.eventtest D/MyView.class: ViewGroup_intercept_DOWN
2020-11-04 20:31:00.926 6527-6527/com.cl.eventtest D/MyView.class: ViewGroup_onTouch_DOWN
2020-11-04 20:31:00.938 6527-6527/com.cl.eventtest D/MyView.class: Activity_dispatch_MOVE
2020-11-04 20:31:00.938 6527-6527/com.cl.eventtest D/MyView.class: ViewGroup_dispacth_MOVE
2020-11-04 20:31:00.938 6527-6527/com.cl.eventtest D/MyView.class: ViewGroup_onTouch_MOVE
2020-11-04 20:31:00.959 6527-6527/com.cl.eventtest D/MyView.class: Activity_dispatch_MOVE
2020-11-04 20:31:00.959 6527-6527/com.cl.eventtest D/MyView.class: ViewGroup_dispacth_MOVE
2020-11-04 20:31:00.959 6527-6527/com.cl.eventtest D/MyView.class: ViewGroup_onTouch_MOVE
2020-11-04 20:31:00.959 6527-6527/com.cl.eventtest D/MyView.class: Activity_dispatch_UP
2020-11-04 20:31:00.959 6527-6527/com.cl.eventtest D/MyView.class: ViewGroup_dispacth_UP
2020-11-04 20:31:00.959 6527-6527/com.cl.eventtest D/MyView.class: ViewGroup_onTouch_UP

此時事件不會再向下至 View 分發，同時 也不會向上傳遞到 Activity 處理。

 

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