android 再按一次后退键退出应用程序

 private static Boolean isExit = false;
    private static Boolean hasTask = false;
    private static final int TIMER_DELAY_TIME=2000;
    Timer mExit = new Timer();
    TimerTask task=null;
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent event) {
        if (keyCode == KeyEvent.KEYCODE_BACK) {
            if(!isExit ) {
                isExit = true;
                Toast.makeText(this, "再按一次退出应用程序", Toast.LENGTH_SHORT).show();
                if(!hasTask) {
                    hasTask=true;
                    if(task!=null){
                        task.cancel();  
                    }
                    task = new TimerTask() {
                        @Override
                        public void run() {
                            isExit = false;
                            hasTask = false;
                        }
                    };
                    mExit.schedule(task, TIMER_DELAY_TIME);
                }
            } else {
                AppAplication.newInstance().exit();
            }
        }
        return true;

    }

代码二：

android连续按两次返回退出程序（完整代码）
UserHelper

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 {@Overridepublic void run() {UserHelper.setIsExit(false);}}

Tab1Activity

// 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;}

需要注意的是每次放定时任务前，确保之前任务已从定时器队列中移除，每次放任务都要新建一个对象，否则出现一下错误：ERROR/AndroidRuntime(11761): java.lang.IllegalStateException: TimerTask is scheduled already，同一个定时器任务只能被放置一次。