登录超时自动退出，计算时间差-b

// 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];
}