android单击返回键两次退出

1. 需求：单击返回键两次退出，单击一次返回键Toast提示,在其后2s内再单击一次返回键就退出。
2.        private static Boolean isExit = false;
3.        private static Boolean hasTask = false;
4.         Timer tExit = new Timer();
5.         TimerTask task = new TimerTask() {
6.                 @Override
7.                 public void run() {
8.                         isExit = false;
9.                         hasTask = true;
10.                 }
11.         };
13.         @Override
14.         public boolean onKeyDown(int keyCode, KeyEvent event) {
15.                 if (keyCode == KeyEvent.KEYCODE_BACK) {
16.                         if (isExit == false) {
17.                                 isExit = true;
18.                                 Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();
19.                                 if (!hasTask) {
20.                                         tExit.schedule(task, 2000);
21.                                 }
22.                         } else {
23.                                 finish();
24.                                 System.exit(0);
25.                         }
26.                 }
27.                 return false;
28.         }