// 此方法适用于所有被创建过的controller，且当前controller生命周期存在，如有错误的地方望大神斧正

// 说一下我们的需求和实现原理，需求：在点击home键退出但没有滑飞它，5分钟之后需要重新登录(其实和平安一账通的登录很像) ；实现原理：添加观察者，不用我们手动发送通知，系统会自动发送通知，计算时间差，然后就可以啦😆

// 贴代码图片

屏幕快照 2016-09-22 下午2.54.31.png

// 我是控制的300s，就是5分钟，超过就弹个框，点击后退出

屏幕快照 2016-09-22 下午3.23.01.png

// 贴代码

• (void)viewWillAppear:(BOOL)animated {
  [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appDidEnterBackgroundNotification) name:UIApplicationDidEnterBackgroundNotification object:nil];
  [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appWillEnterForegroundNotification) name:UIApplicationWillEnterForegroundNotification object:nil];
  }

• (void)appDidEnterBackgroundNotification{
  NSDate *date = [NSDate date];
  NSUserDefaults *user = [NSUserDefaults standardUserDefaults];
  [user setObject:date forKey:K_LOGOUTTIME_KEY];
  [user synchronize];
  NSLog(@"存储时间 =============== ======= %@",date);
  }

• (void)appWillEnterForegroundNotification {
  NSDate *dateLast = [[NSUserDefaults standardUserDefaults] objectForKey:K_LOGOUTTIME_KEY];
  NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
  [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
  NSString *strDate = [dateFormatter stringFromDate:dateLast];
  [self intervalSinceNow:strDate];
  }

// 计算某一时间到当前时间

• (NSString *)intervalSinceNow: (NSString *) theDate
  {
  NSArray timeArray=[theDate componentsSeparatedByString:@"."];
  theDate=[timeArray objectAtIndex:0];
  NSDateFormatter date=[[NSDateFormatter alloc] init];
  [date setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
  NSDate d=[date dateFromString:theDate];
  NSTimeInterval late=[d timeIntervalSince1970]1;
  NSDate dat = [NSDate date];
  NSTimeInterval now=[dat timeIntervalSince1970]1;
  NSString *timeString=@"";
  NSTimeInterval cha= fabs(late-now); // 求绝对值
  timeString = [NSString stringWithFormat:@"%f", cha];
  timeString = [timeString substringToIndex:timeString.length-7];
  if ([timeString intValue] > 300) {
  HPAlertController *alert = [[HPAlertController alloc]initWithViewController:self];
  AlertData *data = [AlertData alertDataTarget:self Title:@"提示" message:@"您登录超时了哦~" itemTitleSelectorStrPairs:@"确认",@"ensureLogAgain",nil];
  [alert showAlertWithData:data];
  }
  return timeString;
  }

• (void)ensureLogAgain {
  [self logoutViewController];

}

// 如果监听通知写在viewDidLoad里面，就不用再移除啦

• (void)viewDidDisappear:(BOOL)animated {
  [[NSNotificationCenter defaultCenter]removeObserver:self];
  }