1 //第一次点击事件发生的时间
 2 private long mExitTime;
 3 
 4 /**
 5  * 点击两次返回退出app
 6  */
 7 @Override
 8 public boolean onKeyDown(int keyCode, KeyEvent event) {
 9     if (keyCode == KeyEvent.KEYCODE_BACK) {
10         if ((System.currentTimeMillis() - mExitTime) > 2000) {
11             Object mHelperUtils;
12             Toast.makeText(this, "再按一次退出APP", Toast.LENGTH_SHORT).show();
13             //System.currentTimeMillis()系统当前时间
14             mExitTime = System.currentTimeMillis();
15         } else {
16             finish();
17         }
18         return true;
19     }
20     return super.onKeyDown(keyCode, event);
21 }