@Override public boolean onKeyDown(int keyCode, KeyEvent event) { if (keyCode == KeyEvent.KEYCODE_BACK) { if ((System.currentTimeMillis() - exitTime) > 2000) { Toast.makeText(getApplicationContext(), "再按一次退出程序", Toast.LENGTH_SHORT).show(); exitTime = System.currentTimeMillis(); } else { finish(); System.exit(0); } return false; } return super.onKeyDown(keyCode, event); }