Android之View的TouchDelegate，你真的理解事件分发了吗？？？

有人问我事件分发是分发给View的吗？

我笃定的说是的，结果不是的。

其实View有一个TouchDelegate，可以给他设置这样一个东西，来使得你的事件触摸范围会被增大！简直牛X！

这个类的全部源码及部分注释

public class TouchDelegate {

    /**
     * View that should receive forwarded touch events
     */
    private View mDelegateView;

    /**
     * Bounds in local coordinates of the containing view that should be mapped to the delegate
     * view. This rect is used for initial hit testing.
     */
    private Rect mBounds;//你要扩大的这个新区域

    /**
     * mBounds inflated to include some slop. This rect is to track whether the motion events
     * should be considered to be be within the delegate view.
     */
    private Rect mSlopBounds;//给mBounds稍微扩大点，其目的是消除触摸误差

    /**
     * True if the delegate had been targeted on a down event (intersected mBounds).
     */
    private boolean mDelegateTargeted;

    /**
     * The touchable region of the View extends above its actual extent.
     */
    public static final int ABOVE = 1;

    /**
     * The touchable region of the View extends below its actual extent.
     */
    public static final int BELOW = 2;

    /**
     * The touchable region of the View extends to the left of its
     * actual extent.
     */
    public static final int TO_LEFT = 4;

    /**
     * The touchable region of the View extends to the right of its
     * actual extent.
     */
    public static final int TO_RIGHT = 8;

    private int mSlop;

    /**
     * Constructor
     *
     * @param bounds Bounds in local coordinates of the containing view that should be mapped to
     *        the delegate view
     * @param delegateView The view that should receive motion events
     */
    public TouchDelegate(Rect bounds, View delegateView) {//构造函数：rect是实际触摸区域，view是要修改触摸区域的view
        mBounds = bounds;

        mSlop = ViewConfiguration.get(delegateView.getContext()).getScaledTouchSlop();//这里就是设定一个值，如果你的滑动距离超过这个值，那么这一次就是有效滑动
        mSlopBounds = new Rect(bounds);
        mSlopBounds.inset(-mSlop, -mSlop);//就是上面讲的溢出区域，防止触摸误差
        mDelegateView = delegateView;
    }

    /**
     * Will forward touch events to the delegate view if the event is within the bounds
     * specified in the constructor.
     *
     * @param event The touch event to forward
     * @return True if the event was forwarded to the delegate, false otherwise.
     */
    public boolean onTouchEvent(MotionEvent event) {//这里是核心代码了：如果你落在这个rect区域内，就判定你是落在这个view内了，view自然就可以获取这次事件
        int x = (int)event.getX();
        int y = (int)event.getY();
        boolean sendToDelegate = false;
        boolean hit = true;
        boolean handled = false;

        switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            Rect bounds = mBounds;

            if (bounds.contains(x, y)) {
                mDelegateTargeted = true;
                sendToDelegate = true;
            }
            break;
        case MotionEvent.ACTION_UP:
        case MotionEvent.ACTION_MOVE:
            sendToDelegate = mDelegateTargeted;
            if (sendToDelegate) {//这里的代码需要解释下，溢出区域，其实是反溢出，是通过比我们设定的rect区域小来进行的一个防止误差，所以你触摸到了rect，不一定有效
                Rect slopBounds = mSlopBounds;
                if (!slopBounds.contains(x, y)) {
                    hit = false;
                }
            }
            break;
        case MotionEvent.ACTION_CANCEL:
            sendToDelegate = mDelegateTargeted;
            mDelegateTargeted = false;
            break;
        }
        if (sendToDelegate) {
            final View delegateView = mDelegateView;

            if (hit) {
                // Offset event coordinates to be inside the target view]

                event.setLocation(delegateView.getWidth() / 2, delegateView.getHeight() / 2);//如果说是在rect区域内，那么就把event的位置修改在view的中心，模拟触摸事件是真的落在了view内了

            } else {
                // Offset event coordinates to be outside the target view (in case it does
                // something like tracking pressed state)
                int slop = mSlop;
                event.setLocation(-(slop * 2), -(slop * 2));
            }
            handled = delegateView.dispatchTouchEvent(event);
        }
        return handled;
    }
}

看看view是如何使用TouchDelegate的，在它的onTouchEvent里，首先就进行了一个判断

if (mTouchDelegate != null) {
    if (mTouchDelegate.onTouchEvent(event)) {
        return true;
    }
}

但是实战的时候，又发现不是这么一回事了，我的理解完全出现了偏差

其真正含义是，当你触摸一个view的时候，而且touch delegate的矩形区域也在这个view里，你触摸到了这块区域，那么这个view就可以把事件转发给delegate类中维护的那个view