Android ViewGroup触摸事件拦截详解

// DOWN中没有对事件进行拦截，因此可以被TouchTv进行处理
10-01 20:32:05.017: D/TouchLayout#   onInterceptTouchEvent(573): ### action -->  ACTION_DOWN
// TouchTv事件分发
10-01 20:32:05.017: D/TouchTv#dispatchTouchEvent(573): ### action -->  ACTION_DOWN
// TouchTv对事件进行处理，TouchTv的onTouchEvent返回false，导致事件交给TouchLayout的onTouchEvent处理
10-01 20:32:05.017: D/TouchTv#onTouchEvent(573): ### action -->  ACTION_DOWN
// TouchLayout的onTouchEvent处理DOWN事件
10-01 20:32:05.017: D/TouchLayout# *** onTouchEvent(573): ### action -->  ACTION_DOWN
// TouchLayout的onTouchEvent处理后续事件
10-01 20:32:05.062: D/TouchLayout# *** onTouchEvent(573): ### action -->  ACTION_MOVE
10-01 20:32:05.082: D/TouchLayout# *** onTouchEvent(573): ### action -->  ACTION_MOVE
10-01 20:32:05.267: D/TouchLayout# *** onTouchEvent(573): ### action -->  ACTION_MOVE
10-01 20:32:05.287: D/TouchLayout# *** onTouchEvent(573): ### action -->  ACTION_MOVE
10-01 20:32:05.307: D/TouchLayout# *** onTouchEvent(573): ### action -->  ACTION_MOVE
10-01 20:32:05.307: D/TouchLayout# *** onTouchEvent(573): ### action -->  ACTION_MOVE
10-01 20:32:05.312: D/TouchLayout# *** onTouchEvent(573): ### action -->  ACTION_UP

// 事件拦截onInterceptTouchEvent
10-01 20:16:03.617: D/TouchLayout#   onInterceptTouchEvent(32675): ### action -->  ACTION_DOWN
// 事件处理onTouchEvent
10-01 20:16:03.617: D/TouchLayout# *** onTouchEvent(32675): ### action -->  ACTION_DOWN
// TouchLayout的dispatchTouchEvent最终返回了false,
10-01 20:16:03.617: D/TouchLayout(32675): ### dispatchTouchEvent, return false
// 事件没有被处理，最终交给了Activity的onTouchEvent处理
10-01 20:16:03.617: D/activity onTouchEvent(32675): ### action -->  ACTION_DOWN
10-01 20:16:03.697: D/activity onTouchEvent(32675): ### action -->  ACTION_MOVE
10-01 20:16:03.712: D/activity onTouchEvent(32675): ### action -->  ACTION_MOVE
10-01 20:16:03.732: D/activity onTouchEvent(32675): ### action -->  ACTION_MOVE
10-01 20:16:03.882: D/activity onTouchEvent(32675): ### action -->  ACTION_MOVE
10-01 20:16:03.897: D/activity onTouchEvent(32675): ### action -->  ACTION_MOVE
10-01 20:16:03.917: D/activity onTouchEvent(32675): ### action -->  ACTION_UP

/** 
 * {@inheritDoc} 
 */  
@Override  
public boolean dispatchTouchEvent(MotionEvent ev) {  
    if (!onFilterTouchEventForSecurity(ev)) {  
        return false;  
    }  
  
    final int action = ev.getAction();  
    final float xf = ev.getX();  
    final float yf = ev.getY();  
    final float scrolledXFloat = xf + mScrollX;  
    final float scrolledYFloat = yf + mScrollY;  
    final Rect frame = mTempRect;  
    // 是否禁用拦截，如果为true表示不能拦截事件；反之，则为可以拦截事件  
    boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;  
    // ACTION_DOWN事件，即按下事件  
    if (action == MotionEvent.ACTION_DOWN) {  
        if (mMotionTarget != null) {  
            mMotionTarget = null;  
        }  
        // If we‘re disallowing intercept or if we‘re allowing and we didn‘t  
        // intercept。如果不允许事件拦截或者不拦截该事件，那么执行下面的操作  
        if (disallowIntercept || !onInterceptTouchEvent(ev))         // 1、是否禁用拦截、是否拦截事件的判断  
            // reset this event‘s action (just to protect ourselves)  
            ev.setAction(MotionEvent.ACTION_DOWN);  
            // We know we want to dispatch the event down, find a child  
            // who can handle it, start with the front-most child.  
            final int scrolledXInt = (int) scrolledXFloat;  
            final int scrolledYInt = (int) scrolledYFloat;  
            final View[] children = mChildren;  
            final int count = mChildrenCount;  
  
            for (int i = count - 1; i >= 0; i--)        // 2、迭代所有子view，查找触摸事件在哪个子view的坐标范围内  
                final View child = children[i];  
                // 该child是可见的  
                if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE  
                        || child.getAnimation() != null) {  
                    // 3、获取child的坐标范围  
                    child.getHitRect(frame);                 
                    // 4、判断发生该事件坐标是否在该child坐标范围内  
                    if (frame.contains(scrolledXInt, scrolledYInt))      
                        // offset the event to the view‘s coordinate system  
                        final float xc = scrolledXFloat - child.mLeft;  
                        final float yc = scrolledYFloat - child.mTop;  
                        ev.setLocation(xc, yc);  
                        child.mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;  
                        // 5、child处理该事件，如果返回true，那么mMotionTarget为该child。正常情况下,  
                        // dispatchTouchEvent(ev)的返回值即onTouchEcent的返回值。因此onTouchEcent如果返回为true，  
                        // 那么mMotionTarget为触摸事件所在位置的child。  
                        if (child.dispatchTouchEvent(ev))       
                            // 6、 mMotionTarget为该child
                            mMotionTarget = child;  
                            return true;  
                        }  
               
                    }  
                }  
            }  
        }  
    }// end if  
  
    boolean isUpOrCancel = (action == MotionEvent.ACTION_UP) ||  
            (action == MotionEvent.ACTION_CANCEL);  
  
    if (isUpOrCancel) {  
        // Note, we‘ve already copied the previous state to our local  
        // variable, so this takes effect on the next event  
        mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;  
    }  
  
  	// 触摸事件的目标view, 即触摸所在的view
    final View target = mMotionTarget;  
    // 7、如果mMotionTarget为空，那么执行super.super.dispatchTouchEvent(ev)，  
    // 即View.dispatchTouchEvent(ev),就是该View Group自己处理该touch事件，只是又走了一遍View的分发过程而已.  
    // 拦截事件或者在不拦截事件且target view的onTouchEvent返回false的情况都会执行到这一步.  
    if (target == null) {  
        // We don‘t have a target, this means we‘re handling the  
        // event as a regular view.  
        ev.setLocation(xf, yf);  
        if ((mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {  
            ev.setAction(MotionEvent.ACTION_CANCEL);  
            mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;  
        }  
        return super.dispatchTouchEvent(ev);  
    }  
 
    // 8、如果没有禁用事件拦截，并且onInterceptTouchEvent(ev)返回为true，即进行事件拦截.  ( 似乎总走不到这一步 ??? )  
    if (!disallowIntercept && onInterceptTouchEvent(ev)) {  
        final float xc = scrolledXFloat - (float) target.mLeft;  
        final float yc = scrolledYFloat - (float) target.mTop;  
        mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;  
        ev.setAction(MotionEvent.ACTION_CANCEL);  
        ev.setLocation(xc, yc);  
        //   
        if (!target.dispatchTouchEvent(ev)) {  
            // target didn‘t handle ACTION_CANCEL. not much we can do  
            // but they should have.  
        }  
        // clear the target  
        mMotionTarget = null;  
        // Don‘t dispatch this event to our own view, because we already  
        // saw it when intercepting; we just want to give the following  
        // event to the normal onTouchEvent().  
        return true;  
    }  
  
    if (isUpOrCancel) {  
        mMotionTarget = null;  
    }  
  
    // finally offset the event to the target‘s coordinate system and  
    // dispatch the event.  
    final float xc = scrolledXFloat - (float) target.mLeft;  
    final float yc = scrolledYFloat - (float) target.mTop;  
    ev.setLocation(xc, yc);  
  
    if ((target.mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {  
        ev.setAction(MotionEvent.ACTION_CANCEL);  
        target.mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;  
        mMotionTarget = null;  
    }  
    // 9、事件不拦截，且target view在ACTION_DOWN时返回true，那么后续事件由target来处理事件  
    return target.dispatchTouchEvent(ev);  
}