问Android：如何实现监视从右到左的滑动手势？

import android.content.Context;

import android.view.GestureDetector;

import android.view.GestureDetector.SimpleOnGestureListener;

import android.view.MotionEvent;

import android.view.View;

import android.view.View.OnTouchListener;

public class OnSwipeTouchListener implements OnTouchListener {

    private final GestureDetector gestureDetector;

    public OnSwipeTouchListener (Context ctx){

        gestureDetector = new GestureDetector(ctx, new GestureListener());

    }

    @Override

    public boolean onTouch(View v, MotionEvent event) {

        return gestureDetector.onTouchEvent(event);

    }

    private final class GestureListener extends SimpleOnGestureListener {

        private static final int SWIPE_THRESHOLD = 100;

        private static final int SWIPE_VELOCITY_THRESHOLD = 100;

        @Override

        public boolean onDown(MotionEvent e) {

            return true;

        }

        @Override

        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {

            boolean result = false;

            try {

                float diffY = e2.getY() - e1.getY();

                float diffX = e2.getX() - e1.getX();

                if (Math.abs(diffX) > Math.abs(diffY)) {

                    if (Math.abs(diffX) > SWIPE_THRESHOLD && Math.abs(velocityX) > SWIPE_VELOCITY_THRESHOLD) {

                        if (diffX > 0) {

                            onSwipeRight();

                        } else {

                            onSwipeLeft();

                        }

                        result = true;

                    }

                }

                else if (Math.abs(diffY) > SWIPE_THRESHOLD && Math.abs(velocityY) > SWIPE_VELOCITY_THRESHOLD) {

                    if (diffY > 0) {

                        onSwipeBottom();

                    } else {

                        onSwipeTop();

                    }

                    result = true;

                }

            } catch (Exception exception) {

                exception.printStackTrace();

            }

            return result;

        }

    }

    public void onSwipeRight() {

    }

    public void onSwipeLeft() {

    }

    public void onSwipeTop() {

    }

    public void onSwipeBottom() {

    }

}

imageView.setOnTouchListener(new OnSwipeTouchListener(MyActivity.this) {

    public void onSwipeTop() {

        Toast.makeText(MyActivity.this, "top", Toast.LENGTH_SHORT).show();

    }

    public void onSwipeRight() {

        Toast.makeText(MyActivity.this, "right", Toast.LENGTH_SHORT).show();

    }

    public void onSwipeLeft() {

        Toast.makeText(MyActivity.this, "left", Toast.LENGTH_SHORT).show();

    }

    public void onSwipeBottom() {

        Toast.makeText(MyActivity.this, "bottom", Toast.LENGTH_SHORT).show();

    }

});