Are performSelector afterDelay calls reset when applicationDidEnterBackground?

Question

I totally understand if they are, but what I'm looking for is a timer that pauses when the application enters the background and unpauses after the user returns to the app. I do not need a background task; I just want to make sure that after approximately x minutes within the app a certain action occurs whether that is today or tomorrow.

Thanks! Brett

Answer 1

Backgrounding the app (assuming you have no background task) doesn't "pause" the timer. It's still counting down in theory so if the app is reopened, it will fire if enough time has passed. This goes for NSTimer's as well. (Let me know if you want more details as to why and I'll edit the answer).

Consider using the following code:

@implementation MyCustomClass {
    int elapsedTime;
    NSTimer *timer;
}

- (id) init {
    if ( ( self = [super init] ) ) {
        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(applicationEnteredBackground)
                                                     name:UIApplicationDidEnterBackgroundNotification
                                                   object:nil];
        [[NSNotificationCenter defaultCenter] addObserver:self
                                                 selector:@selector(applicationEnteredForeground)
                                                     name:UIApplicationDidBecomeActiveNotification
                                                   object:nil];
    }
    return self;
}


- (void) applicationEnteredForeground { 
    timer = [NSTimer timerWithTimeInterval:1
                                    target:self
                                  selector:@selector(timerTicked)
                                  userInfo:nil
                                   repeats:YES];
    [[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
}

- (void) applicationEnteredBackground {
    [timer invalidate];
}

- (void) timerTicked {
    elapsedTime += 1;
    // If enough time passed, do something
}