//双击退出事件
     @Override
     public boolean onKeyDown(int keyCode, KeyEvent event) {
         if(keyCode == KeyEvent.KEYCODE_BACK){
                  ExitApp();      //调用双击退出函数
             }
         return false;
     }
     private long exitTime = 0;
     public void ExitApp() {
         if ((System.currentTimeMillis() - exitTime) > 2000){
             Snackbar.make(lstData, "再按一次退出程序", Snackbar.LENGTH_LONG).setAction("Action", null).show();
             exitTime = System.currentTimeMillis();
         } else {
             finish();
             System.exit(0);
         }
     }