android - 如何在 subview 和父 View 组触摸事件之间变化

Question

我决定发布这个问题和答案以回应 to this comment对于这个问题:
How to handle click in the child Views, and touch in the parent ViewGroups?

我会把评论贴在这里:

Suppose I want to override the touch events only for handling some of the children, what can I do inside this function to have it working ? I mean, for some children it would work as usual, and for some, the parent-view will decide if they will get the touch events or not.

所以问题是这样的:如何防止父 onTouchEvent() 覆盖某些子元素的 onTouchEvent()，同时让它覆盖其他子元素的 onTouchEvent() ?

Answer 1

1. 嵌套 View 组的 onTouchEvents() 可以由 boolean onInterceptTouchEvent 管理.

OnInterceptTouchEvent 的默认值为 false。

parent 的onTouchEvent 在 child 之前收到。如果 OnInterceptTouchEvent 返回 false，它会将运动事件沿链向下发送到子级的 OnTouchEvent 处理程序。如果它返回 true，则父级将处理触摸事件。

但是，在某些情况下，我们可能希望某些子元素管理 OnTouchEvent，而某些子元素由父 View (或可能是父 View 的父 View )管理。

这可以通过多种方式进行管理。

1. 保护子元素免受父元素 OnInterceptTouchEvent 影响的一种方法是实现 requestDisallowInterceptTouchEvent .

public void requestDisallowInterceptTouchEvent (boolean disallowIntercept)

如果元素启用了事件处理程序，这将阻止任何父 View 管理该元素的 OnTouchEvent。

1. 如果 OnInterceptTouchEvent 为 false，则将评估子元素的 OnTouchEvent。如果您在子元素中有处理各种触摸事件的方法，则任何禁用的相关事件处理程序都会将 OnTouchEvent 返回给父元素。

这个答案:
https://stackoverflow.com/a/13540006/3956566很好地可视化了触摸事件的传播方式:
parent -> child|parent -> child|parent -> subview 。

4. 另一种方法是从 OnInterceptTouchEvent 为父级返回不同的值。

这个例子取自 Managing Touch Events in a ViewGroup并演示了如何在用户滚动时拦截 child 的OnTouchEvent。

4a。

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {
    /*
     * This method JUST determines whether we want to intercept the motion.
     * If we return true, onTouchEvent will be called and we do the actual
     * scrolling there.
     */


    final int action = MotionEventCompat.getActionMasked(ev);

    // Always handle the case of the touch gesture being complete.
    if (action == MotionEvent.ACTION_CANCEL || action == MotionEvent.ACTION_UP) {
        // Release the scroll.
        mIsScrolling = false;
        return false; // Do not intercept touch event, let the child handle it
    }

    switch (action) {
        case MotionEvent.ACTION_MOVE: {
            if (mIsScrolling) {
                // We're currently scrolling, so yes, intercept the 
                // touch event!
                return true;
            }

            // If the user has dragged her finger horizontally more than 
            // the touch slop, start the scroll

            // left as an exercise for the reader
            final int xDiff = calculateDistanceX(ev); 

            // Touch slop should be calculated using ViewConfiguration 
            // constants.
            if (xDiff > mTouchSlop) { 
                // Start scrolling!
                mIsScrolling = true;
                return true;
            }
            break;
        }
        ...
    }

    // In general, we don't want to intercept touch events. They should be 
    // handled by the child view.
    return false;
}

编辑:回答评论。
这是来自同一链接的一些代码，展示了如何在元素周围创建矩形的参数:
4b。

// The hit rectangle for the ImageButton
myButton.getHitRect(delegateArea);

// Extend the touch area of the ImageButton beyond its bounds
// on the right and bottom.
delegateArea.right += 100;
delegateArea.bottom += 100;

// Instantiate a TouchDelegate.
// "delegateArea" is the bounds in local coordinates of 
// the containing view to be mapped to the delegate view.
// "myButton" is the child view that should receive motion
// events.
TouchDelegate touchDelegate = new TouchDelegate(delegateArea, myButton);

// Sets the TouchDelegate on the parent view, such that touches 
// within the touch delegate bounds are routed to the child.
if (View.class.isInstance(myButton.getParent())) {
    ((View) myButton.getParent()).setTouchDelegate(touchDelegate);
}