在android上实现手势放大缩小功能

package com.example.eventtest;  
  
import java.util.ArrayList;  
  
import android.os.Bundle;  
import android.app.Activity;  
import android.gesture.GestureOverlayView;  
import android.gesture.GestureOverlayView.OnGestureListener;  
import android.graphics.Point;  
import android.view.Menu;  
import android.view.MotionEvent;  
import android.view.View;  
import android.view.View.OnClickListener;  
import android.widget.Toast;  
  
public class MainActivity extends Activity {  
  
      
    double nLenStart = 0;  
      
      
    @Override  
    protected void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.activity_main);  
    }  
      
      
    @Override  
    public boolean onTouchEvent(MotionEvent event) {      
                  
        int nCnt = event.getPointerCount();  
          
        int n = event.getAction();  
        if( (event.getAction()&MotionEvent.ACTION_MASK) == MotionEvent.ACTION_POINTER_DOWN && 2 == nCnt)//<span style="color:#ff0000;">2表示两个手指</span>  
        {  
                      
            for(int i=0; i< nCnt; i++)  
            {  
                float x = event.getX(i);  
                float y = event.getY(i);  
                  
                Point pt = new Point((int)x, (int)y);  
      
            }  
              
            int xlen = Math.abs((int)event.getX(0) - (int)event.getX(1));  
            int ylen = Math.abs((int)event.getY(0) - (int)event.getY(1));  
              
            nLenStart = Math.sqrt((double)xlen*xlen + (double)ylen * ylen);  
              
              
        }else if( (event.getAction()&MotionEvent.ACTION_MASK) == MotionEvent.ACTION_POINTER_UP  && 2 == nCnt)  
        {  
              
            for(int i=0; i< nCnt; i++)  
            {  
                float x = event.getX(i);  
                float y = event.getY(i);  
                  
                Point pt = new Point((int)x, (int)y);  
  
            }  
              
            int xlen = Math.abs((int)event.getX(0) - (int)event.getX(1));  
            int ylen = Math.abs((int)event.getY(0) - (int)event.getY(1));  
              
            double nLenEnd = Math.sqrt((double)xlen*xlen + (double)ylen * ylen);  
              
            if(nLenEnd > nLenStart)//通过两个手指开始距离和结束距离，来判断放大缩小  
            {  
                Toast.makeText(getApplicationContext(), "放大", 3000).show();  
            }  
            else  
            {  
                Toast.makeText(getApplicationContext(), "缩小", 3000).show();  
            }  
        }  

getAction()方法返回的是int类型，用到的只有低16位，其中：低八位是动作的类型，高8位是触摸点索引值的表示（单点为0，双点为1）

获得动作类型： int action = event.getAction() & ACTION_MASK

　　 或者使用 getActionMasked()

获得触摸点索引类型： int pointerIndex = (event.getAction() & ACTION_POINTER_INDEX_MASK ) >> ACTION_POINTER_INDEX_SHIFT

　　或者使用 getActionIndex()

          
          
      
        return super.onTouchEvent(event);  
    }  
  
  
}