Method to pass object(s) to child ViewControllers from parent ViewController. In this case a UITabBarController passes a modelobject to each of it's child views that support a given @selector. Container views (ie UINavigationController, UITabBarControlle

DZTabBarController.m

- (void)viewDidLoad
{
    [super viewDidLoad];
    self.dangerZones = [[DZStoredObjects alloc] init];
    // Create a stack and load it with the view controllers from
    // our tabs.
    NSMutableArray *stack = [NSMutableArray arrayWithArray:self.viewControllers];
    // While we still have items on our stack
    while ([stack count] > 0) {
        // pop the last item off the stack.
        id controller = [stack lastObject];
        [stack removeLastObject];
        // If it is a container object, add its controllers to
        // the stack.
        if ([controller respondsToSelector:@selector(viewControllers)]) {
            [stack addObjectsFromArray:[controller viewControllers]];
        }
        // If it responds to setWeightHistory, set the weight
        // history.
        if ([controller respondsToSelector:@selector(setDangerZones:)]) {
            [controller setDangerZones:self.dangerZones];

        }
    }
}