[转]android两次按返回键退出程序实现

1. private static Boolean isExit = false;  
2.     private static Boolean hasTask = false;  
3.     Timer tExit = new Timer();  
4.     TimerTask task = new TimerTask() {  
5.            
6.         @Override  
7.         public void run() {  
8.             isExit = false;  
9.             hasTask = true;  
10.         }  
11.     };  
12.   
13.   
14. public boolean onKeyDown(int keyCode, KeyEvent event) {  
15.                 // TODO Auto-generated method stub  
16.                 if(keyCode == KeyEvent.KEYCODE_BACK){  
17. //                        System.out.println("user back down");  
18.                         if(isExit == false ) {  
19.                                 isExit = true;  
20.                                 Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();  
21.                                 if(!hasTask) {  
22.                                         tExit.schedule(task, 2000);  
23.                                 }} else {  
24.                                                                                 }  
25.                                 finish();  
26.                                 System.exit(0);  
27.                         }  
28.                 }                          
29.                 return false;  
30.         }