android延续按两次返回退出程序（完整代码）

package com.hk.icie;public class UserHelper {		private static Boolean isExit = false;	public static Boolean getIsExit() {		return isExit;	}	public static void setIsExit(Boolean isExit) {		UserHelper.isExit = isExit;	}}

ExitTimerTask

package com.hk.utils;import java.util.TimerTask;import com.hk.icie.UserHelper;public class ExitTimerTask extends TimerTask {	@Override	public void run() {		UserHelper.setIsExit(false);	}}

// 此部分为了实现按两下返回退出private Timer tExit = new Timer();private ExitTimerTask exitTimerTask = new ExitTimerTask();@Overridepublic boolean onKeyDown(int keyCode, KeyEvent event) {	if (keyCode == KeyEvent.KEYCODE_BACK) {		if (!UserHelper.getIsExit()) {			UserHelper.setIsExit(true);			AlertUtils.ToastAlert(Tab1Activity.this, R.string.alert_exit);			if (tExit != null) {				if (exitTimerTask != null) {					// 将原任务从队列中移除(必须的，否则报错)					exitTimerTask.cancel();				}				// 新建一个任务				exitTimerTask = new ExitTimerTask();				tExit.schedule(exitTimerTask, 2*1000);			}		}		else {			UserHelper.setIsExit(false);			finish();			System.exit(0);		}	}	return true;}