Android 用Activity的onTouchEvent来监听滑动手势

package com.example.activityOnTouchEvent;

import android.app.Activity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.widget.Toast;

public class MyActivity extends Activity {
    //手指按下的点为(x1, y1)手指离开屏幕的点为(x2, y2)
    float x1 = 0;
    float x2 = 0;
    float y1 = 0;
    float y2 = 0;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        //继承了Activity的onTouchEvent方法，直接监听点击事件
        if(event.getAction() == MotionEvent.ACTION_DOWN) {
            //当手指按下的时候
            x1 = event.getX();
            y1 = event.getY();
        }
        if(event.getAction() == MotionEvent.ACTION_UP) {
            //当手指离开的时候
            x2 = event.getX();
            y2 = event.getY();
            if(y1 - y2 > 50) {
                Toast.makeText(MyActivity.this, "向上滑", Toast.LENGTH_SHORT).show();
            } else if(y2 - y1 > 50) {
                Toast.makeText(MyActivity.this, "向下滑", Toast.LENGTH_SHORT).show();
            } else if(x1 - x2 > 50) {
                Toast.makeText(MyActivity.this, "向左滑", Toast.LENGTH_SHORT).show();
            } else if(x2 - x1 > 50) {
                Toast.makeText(MyActivity.this, "向右滑", Toast.LENGTH_SHORT).show();
            }
        }
        return super.onTouchEvent(event);
    }

}