android 处理Back键按下事件

package com.example.keyevent;

import android.os.Bundle;  
import android.view.KeyEvent;  
import android.app.Activity;  
/** 
 * Demo描述: 
 * 处理Back键按下事件 
 *  
 * 注意事项: 
 * 以下两种方法勿一起使用 
 */  
public class MainActivity extends Activity {  
  
    @Override  
    protected void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.activity_main);  
    }  
    /** 
     * 监听Back键按下事件,方法1: 
     * super.onBackPressed()会自动调用finish()方法执行 onDestroy(),关闭 
     * 当前Activity. 
     * 若要屏蔽Back键盘,注释该行代码即可 
     */  
    @Override  
    public void onBackPressed() {  
        super.onBackPressed();  
        System.out.println("按下了back键   onBackPressed()");         
    } 
      
      
   /** 
    * 监听Back键按下事件,方法2: 
    * 在此处返回false,所以会继续传播该事件. 继续执行super.onKeyDown(keyCode, event);  
    */  
   @Override  
    public boolean onKeyDown(int keyCode, KeyEvent event) {  
        if ((keyCode == KeyEvent.KEYCODE_BACK)) {  
             System.out.println("按下了back键   onKeyDown()");   
             return false;  
        }else {  
            return super.onKeyDown(keyCode, event);  
        }  
    }  
      
    @Override  
    protected void onDestroy() {  
        super.onDestroy();  
        System.out.println("执行 onDestroy()");  
    }     
}