private static Boolean isQuit = false;

Timer timer = new Timer();

@Override

public boolean onKeyDown(int keyCode, KeyEvent event) {

if (keyCode == KeyEvent.KEYCODE_BACK) {

if (isQuit == false) {

isQuit = true;

Toast.makeText(getBaseContext(), "再按一次返回键退出程序", Toast.LENGTH_SHORT).show();

TimerTask task = null;

task = new TimerTask() {

@Override

public void run() {

isQuit = false;

}

};

timer.schedule(task, 2000);

} else {

finish();

System.exit(0);

}

}

return false;

}