GridView在手势/滑动时选择多个项目

Question

我想在左侧或右侧滑动时在gridview中选择多个项目。现在向左或向右滑动仅适用于单个项目，而我想在滑动时选择多个项目。我在这里理解onFling方法被调用。在stackoverflow中的其他答案之后，我使用了以下代码：

import android.support.v4.view.GestureDetectorCompat;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.GridView;

public class MainActivity extends AppCompatActivity {

    private GestureDetectorCompat detector;

    static final String[] numbers = new String[] {
            "A", "B", "C", "D", "E",
            "F", "G", "H", "I", "J",
            "K", "L", "M", "N", "O",
            "P", "Q", "R", "S", "T",
            "U", "V", "W", "X", "Y", "Z"};


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        GridView gridView = (GridView) findViewById(R.id.gridView);

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
                android.R.layout.simple_list_item_1, numbers);

        gridView.setAdapter(adapter);

        detector = new GestureDetectorCompat(this, new MyGestureListener());


        gridView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                detector.onTouchEvent(event);
                return false;
            }

        });
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        detector.onTouchEvent(event);
        return super.onTouchEvent(event);
    }

    class MyGestureListener extends GestureDetector.SimpleOnGestureListener {

        private static final int SWIPE_THRESHOLD = 100;
        private static final int SWIPE_VELOCITY_THRESHOLD = 100;

        @Override
        public boolean onDown(MotionEvent event) {
            return true;
        }

        @Override
        public boolean onFling(MotionEvent event1, MotionEvent event2,
                               float velocityX, float velocityY) {

            float diffY = event2.getY() - event1.getY();
            float diffX = event2.getX() - event1.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();
                    }
                }
            } else {
                if (Math.abs(diffY) > SWIPE_THRESHOLD && Math.abs(velocityY) > SWIPE_VELOCITY_THRESHOLD) {
                    if (diffY > 0) {
                        onSwipeBottom();
                    } else {
                        onSwipeTop();
                    }
                }
            }
            return true;
        }
    }

    private void onSwipeLeft() {
        Log.d("left", "clicked!");
    }

    private void onSwipeRight() {
        Log.d("right", "clicked!");
    }

    private void onSwipeTop() {
        Log.d("top", "clicked!");
    }

    private void onSwipeBottom() {
        Log.d("bottom", "clicked!");
    }
}