MotionEvent事件在onInterceptTouchEvent()、onTouchEvent()中的傳遞順序

onInterceptTouchEvent()用於處理事件並改變事件的傳遞方向。處理事件這個不用說了，你在函數內部編寫代碼處理就可以了。而決定傳遞方向的是返回值，返回為false時事件會傳遞給子控件的onInterceptTouchEvent()；返回值為true時事件會傳遞給當前控件的onTouchEvent()，而不在傳遞給子控件，這就是所謂的Intercept(截斷)。

onTouchEvent() 用於處理事件，返回值決定當前控件是否消費（consume）了這個事件。可能你要問是否消費了又區別嗎，反正我已經針對事件編寫了處理代碼？答案是有區別！比如ACTION_MOVE或者ACTION_UP發生的前提是一定曾經發生了ACTION_DOWN，如果你沒有消費ACTION_DOWN，那麼系統會認為ACTION_DOWN沒有發生過，所以ACTION_MOVE或者ACTION_UP就不能被捕獲。

<?xml version="1.0" encoding="utf-8"?>
<com.touchstudy.LayoutView1 xmlns:Android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >
    <com.touchstudy.LayoutView2
        android:orientation="vertical"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:gravity="center">
       <com.touchstudy.MyTextView 
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:id="@+id/tv"
            android:text="AB"
            android:textSize="40sp"
            android:text
            android:background="#FFFFFF"
            android:textColor="#0000FF"/>
   </com.touchstudy.LayoutView2>
</com.touchstudy.LayoutView1>

在沒有重寫onInterceptTouchEvent()和onTouchEvent()的情況下(他們的返回值都是false), 對上面這個布局，MotionEvent事件的傳遞順序如下：

 

當某個控件的onInterceptTouchEvent()返回值為true時，就會發生截斷，事件被傳到當前控件的onTouchEvent()。如我們將LayoutView2的onInterceptTouchEvent()返回值為true,則傳遞流程變成：

 

 如果我們同時將LayoutView2的onInterceptTouchEvent()和onTouchEvent()設置成true，那麼LayoutView2將消費被傳遞的事件，同時後續事件（如跟著ACTION_DOWN的ACTION_MOVE或者ACTION_UP）會直接傳給LayoutView2的onTouchEvent(),不傳給其他任何控件的任何函數。同時傳遞給子空間一個ACTION_CANCEL事件。傳遞流程變成（圖中沒有畫出ACTION_CANCEL事件）：

          

附SDK給出的說明：

·  You will receive the down event here. ·  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. ·  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(). ·  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 ACTION_CANCEL, and all further events will be delivered to your onTouchEvent() method and no longer appear here.  

示例對應的Java代碼

見 http://www.linuxidc.com/Linux/2011-10/44504.htm