Dealloc is called on UIViewControllers which are stored in a NSMutableDictionary and presented by UIViewControllerContainment

I've built a custom UITabBarController with Storyboards/Segues and UIViewController containment. Here is a link to it: https://github.com/mhaddl/MHCustomTabBarController

The UIViewControllers which will be presented by the Container are stored in a NSMutableDictionary (keys are the segues' identifiers). Everything is working fine until the point is reached where I come back to a earlier presented ViewController. At this moment "dealloc" gets called on this ViewController before it is presented.

How can I prevent "dealloc" from getting called so it can be used to unsubscribe from Notifications, and nil delegates.

MHCustomTabBarController:

    @implementation MHCustomTabBarController {
    NSMutableDictionary *_viewControllersByIdentifier;
}

- (void)viewDidLoad {
    [super viewDidLoad];

    _viewControllersByIdentifier = [NSMutableDictionary dictionary];
}

-(void) viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];

    if (self.childViewControllers.count < 1) {
        [self performSegueWithIdentifier:@"viewController1" sender:[self.buttons objectAtIndex:0]];
    }
}

- (void)willAnimateRotationToInterfaceOrientation:(UIInterfaceOrientation)toInterfaceOrientation duration:(NSTimeInterval)duration {
    self.destinationViewController.view.frame = self.container.bounds;
}



#pragma mark - Segue

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {

    if (![segue isKindOfClass:[MHTabBarSegue class]]) {
        [super prepareForSegue:segue sender:sender];
        return;
    }

    self.oldViewController = self.destinationViewController;

    //if view controller isn't already contained in the viewControllers-Dictionary
    if (![_viewControllersByIdentifier objectForKey:segue.identifier]) {
        [_viewControllersByIdentifier setObject:segue.destinationViewController forKey:segue.identifier];
    }

    for (UIButton *aButton in self.buttons) {
        [aButton setSelected:NO];
    }

    UIButton *button = (UIButton *)sender;
    [button setSelected:YES];
    self.destinationIdentifier = segue.identifier;
    self.destinationViewController = [_viewControllersByIdentifier objectForKey:self.destinationIdentifier];


}

- (BOOL)shouldPerformSegueWithIdentifier:(NSString *)identifier sender:(id)sender {
    if ([self.destinationIdentifier isEqual:identifier]) {
        //Dont perform segue, if visible ViewController is already the destination ViewController
        return NO;
    }

    return YES;
}

#pragma mark - Memory Warning

- (void)didReceiveMemoryWarning {
    [[_viewControllersByIdentifier allKeys] enumerateObjectsUsingBlock:^(NSString *key, NSUInteger idx, BOOL *stop) {
        if (![self.destinationIdentifier isEqualToString:key]) {
            [_viewControllersByIdentifier removeObjectForKey:key];
        }
    }];
}

@end

MHTabBarSegue:

@implementation MHTabBarSegue
- (void) perform {
    MHCustomTabBarController *tabBarViewController = (MHCustomTabBarController *)self.sourceViewController;
    UIViewController *destinationViewController = (UIViewController *) tabBarViewController.destinationViewController;

    //remove old viewController
    if (tabBarViewController.oldViewController) {
        [tabBarViewController.oldViewController willMoveToParentViewController:nil];
        [tabBarViewController.oldViewController.view removeFromSuperview];
        [tabBarViewController.oldViewController removeFromParentViewController];
    }


    destinationViewController.view.frame = tabBarViewController.container.bounds;
    [tabBarViewController addChildViewController:destinationViewController];
    [tabBarViewController.container addSubview:destinationViewController.view];
    [destinationViewController didMoveToParentViewController:tabBarViewController];
}

@end

"At this moment "dealloc" gets called on this ViewController before it is presented." -- no, not really. Dealloc is being called on a controller that never gets on screen, not the one you came from initially or are going back to. The way your segue is set up, and the fact that you keep a reference to your controllers in the dictionary, means that they never get deallocated. Segues (other than unwinds) ALWAYS instantiate new view controllers, so what's happening is that a new instance of, say VC1 is created when you click on the first tab (and a segue is triggered), but you never do anything with that controller (which would be self.destinationViewController in the custom segue class) so it's deallocated as soon as the perform method exits.

Depending on where you setup any delegates or notification observers, this might not be a problem -- this controller that's created, and then immediately deallocated never has its viewDidLoad method called, so if you do those things in viewDidLoad, they won't ever happen for this transient view controller.

If you don't want this to happen, then you need to make your transitions in code without using segues.