hack for preventing multiple method calls in the same time. For example if you have a bug in your code that calls viewWillAppear: two times every time you can just copy/paste this code

hack.m

    // Invalidate a call if it's been less that 1 second since the last one
    //=====================================================================
    static NSDate *lastDate = nil;
    NSDate *currentDate = [NSDate date];
    if (lastDate != nil &&
        [currentDate timeIntervalSinceDate:lastDate] < 1) {
        return ;
    }
    lastDate = currentDate;
    //=====================================================================