再按一次退出程序

现在欧尼create方法外面，写入这两行代码：

  @Override
        public boolean onKeyDown(int keyCode, KeyEvent event) {

              if (keyCode == KeyEvent.KEYCODE_BACK) {
                      if ((System.currentTimeMillis() - mExitTime) > 2000) {
                              Object mHelperUtils;
                              Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();
                              mExitTime = System.currentTimeMillis();

                      } else {
                              finish();
                      }
                      return true;
              }
              return super.onKeyDown(keyCode, event);

        }

再定义属性：

 private long mExitTime;