android再点一次返回退出

 

@Override   
public boolean onKeyDown(int keyCode, KeyEvent event)//主要是对这个函数的复写    
{   
    // TODO Auto-generated method stub     
   
    if((keyCode == KeyEvent.KEYCODE_BACK)&&(event.getAction() == KeyEvent.ACTION_DOWN))   
    {   
        if(System.currentTimeMillis() - temptime >2000) // 2s内再次选择back键有效    
        {   
            System.out.println(Toast.LENGTH_LONG);   
            Toast.makeText(this, "请在按一次返回退出", Toast.LENGTH_LONG).show();   
            temptime = System.currentTimeMillis();   
        }   
        else {   
               finish();    
               System.exit(0); //凡是非零都表示异常退出!0表示正常退出!    
        }   
              
        return true;    
   
    }   
    return super.onKeyDown(keyCode, event);   
}