起因

有时候要求的视图区域很小，但响应区域要求很大。一般解决办法很多，可以用一个透明的布局去回调响应事件，另外也可以采用Deletgate（代理事件），就是把响应区域的事件直接传递到指定的应该响应的view.

使用TouchDelegate

这个解决办法可以指定区域响应，若继承一个ViewGroup应该在onSizeChanged()中去实现。代码如下：

    /*
     * TouchDelegate is applied to this view (parent) to delegate all touches
     * within the specified rectangle to the CheckBox (child). Here, the
     * rectangle is the entire size of this parent view.
     * 
     * This must be done after the view has a size so we know how big to make
     * the Rect, thus we've chosen to add the delegate in onSizeChanged()
     */
    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        if (w != oldw || h != oldh) {
            // Apply the whole area of this view as the delegate area
            Rect bounds = new Rect(0, 0, w, h);
            TouchDelegate delegate = new TouchDelegate(bounds, mButton);
            setTouchDelegate(delegate);
        }
    }

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解决的办法非常简单，但也有一个缺点：

each event forwarded to the 
delegate first has its location reset to the
exact midpoint of the delegate view. This means that if you attempt 
to forward a series of ACTION_MOVE events
through TouchDelegate, the results won’t be what you expect, 
because they will look to the delegate view as
if the finger isn’t really moving at all.

也就是说只会传递一个这个代理view的中心点，滑动事件变化的坐标并不会真实的那样传递。也就是说传递过去的坐标不动的，就是这个view的中心坐标位置。当然这个时候可以通过将坐标传到onTouchEvent()，或者dispatchTouchEvent(event);来解决。