Objective c 当应用程序进入后台状态时，如何添加计时器？

以下是我迄今为止所尝试的：

- (void)applicationWillResignActive:(UIApplication *)application
{

     timer = [NSTimer timerWithTimeInterval:1 target:self selector:@selector(triggerTimer:) userInfo:nil repeats:FALSE];
     NSRunLoop* runLoop = [NSRunLoop currentRunLoop];
     [runLoop addTimer:timer forMode:NSRunLoopCommonModes];
     [runLoop run];
}

- (void)applicationWillEnterForeground:(UIApplication *)application
{
    if (timer && [timer isValid]) {
        [timer invalidate];
     }
}

我的问题是，如果我使计时器无效，runloop仍在运行并冻结我的UI（动画不工作，滚动不工作，等等）。你知道我该怎么做吗

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提前谢谢

您不应该创建计时器

应用程序willresignactive

。相反，您应该将当前日期/时间保存在

ApplicationIdentinterBackground

中

// Not sure how you are keeping session information
// You can use a variable to store session id
// or simple keep a bool to indicate session is valid
// In this example, let say I just keep a session BOOL

- (void)applicationDidEnterBackground:(UIApplication *)application {
   // save the save the app enters background
   backgroundTime_ = [NSDate date];        
}

// In this example I am going to check if my session is valid in two stages
// You can do it in one stage if you like
- (void)applicationWillEnterForeground:(UIApplication *)application {
   // I only need to do a time-out check if I have a valid session
   if (isValidSession_ && backgroundTime_)
   {
       // get the number of second since we entered background
       NSTimeInterval span = [backgroundTime_ timeIntervalSinceNow];
       if (span > (15 * 60))
       {
           isValidSession_ = NO;      
       }
   }

}

// This is wheer the magic occurs
- (void)applicationDidBecomeActive:(UIApplication *)application {
    // check if session is still valid
    if (!isValidSession_)
    {
        // Load the login view
    }
}

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为什么要在后台设置计时器？你想完成什么？如果应用程序在后台运行超过15分钟，请注销用户，然后再次显示登录屏幕。谢谢，它工作得非常好！我在代码中添加了一个小改动，NSTimeInterval span=[[NSDate date]timeIntervalSinceDate:backgroundTime]；所以跨度现在是正的，而不是负的。