java - Android 开发 - GestureDetector.OnGestureListener 或 GestureDetector.SimpleOnGestureListener

Question

我正在编写简单的代码来检测所有手势，如滑动、滚动等，并打算实现接口(interface) GestureDetector.OnGestureListener用于覆盖它的方法，但我知道同样可以用 GestureDetector.SimpleOnGestureListener 完成.据我所知SimpleOnGestureListener是一个实现了 OnGestureListener 的类, OnDoubleTapListener和 OnContextClickListener接口(interface)，如果我错了，请纠正我。

在 Android Developer 网站页面上写着 -

If you only want to process a few gestures, you can extend GestureDetector.SimpleOnGestureListener instead of implementing the GestureDetector.OnGestureListener interface.

GestureDetector.SimpleOnGestureListener provides an implementation for all of the on<TouchEvent> methods by returning false for all of them. Thus you can override only the methods you care about. For example, the snippet below creates a class that extends GestureDetector.SimpleOnGestureListener and overrides onFling() and onDown().

我在这里有几个问题，

1) 为什么要使用GestureDetector.SimpleOnGestureListener如果我们可以实现 GestureDetector.OnGestureListener以及其他使用这些方法的接口(interface)？

2) 是GestureDetector.SimpleOnGestureListener一样没有区别？是为了简化编码？

Answer 1

来自 GestureDetector.SimpleOnGestureListener 的文档

A convenience class to extend when you only want to listen for a subset of all the gestures. This implements all methods in the GestureDetector.OnGestureListener, GestureDetector.OnDoubleTapListener, and GestureDetector.OnContextClickListener but does nothing and return false for all applicable methods.

如果您只想实现一些方法(不是全部)，SimpleOnGestureListener 具有不执行任何操作的默认实现。这可以防止您的代码被多种无所事事的方法弄得乱七八糟。从功能的角度来看，使用 SimpleOnGestureListener 还是直接实现接口(interface)都没有关系。

源代码

public static class SimpleOnGestureListener implements OnGestureListener, OnDoubleTapListener,
        OnContextClickListener {

    public boolean onSingleTapUp(MotionEvent e) {
        return false;
    }

    public void onLongPress(MotionEvent e) {
    }

    public boolean onScroll(MotionEvent e1, MotionEvent e2,
            float distanceX, float distanceY) {
        return false;
    }

    public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,
            float velocityY) {
        return false;
    }

    public void onShowPress(MotionEvent e) {
    }

    public boolean onDown(MotionEvent e) {
        return false;
    }

    public boolean onDoubleTap(MotionEvent e) {
        return false;
    }

    public boolean onDoubleTapEvent(MotionEvent e) {
        return false;
    }

    public boolean onSingleTapConfirmed(MotionEvent e) {
        return false;
    }

    public boolean onContextClick(MotionEvent e) {
        return false;
    }
}