UIViewController reported as responding to addChildViewController: on iOS 4

Question

Has anyone else encountered this? The following code reports "YES" when running on the iOS 4 simulator but according to the Apple docs the method addChildViewController is only available on iOS 5 and later. This doesn't seem like the correct behavior, is this a bug?

if([UIViewController instancesRespondToSelector:@selector(addChildViewController:)]) {
    NSLog(@"YES"); 
} else {
    NSLog(@"NO");
}

Answer 1

I think this is a bug. Calling the addChildViewController seems to run without any warning or error too.

I wrote the following viewDidLoad:

- (void)viewDidLoad
{
    [super viewDidLoad];

    MyChildView *aChildViewController = [[MyChildView alloc] initWithNibName:@"MyChildView" bundle:nil];

    // Do any additional setup after loading the view, typically from a nib.
    SEL mySelector = @selector(addChildViewController:);
    if([UIViewController instancesRespondToSelector:mySelector] == YES) {
        NSLog(@"YES addChildViewController:"); 
        [self addChildViewController:aChildViewController];
    } else {
        NSLog(@"NO addChildViewController:");
    }

    if([UIViewController instancesRespondToSelector:@selector(automaticallyForwardAppearanceAndRotationMethodsToChildViewControllers)] == YES) {
        NSLog(@"YES automaticallyForwardAppearanceAndRotationMethodsToChildViewControllers");

    } else {
        NSLog(@"NO automaticallyForwardAppearanceAndRotationMethodsToChildViewControllers");
    }
}

In the iOS 4.3 Simulator I see following output. Both messages are restricted to IOS 5.0 and higher. It appears addChildViewController is responding in the 4.3 simulator incorrectly. I don't have 4.3 device to test on an actual device.

2011-11-18 09:55:12.161 testViewFunctionality[873:b303] YES addChildViewController:
2011-11-18 09:55:12.162 testViewFunctionality[873:b303] NO automaticallyForwardAppearanceAndRotationMethodsToChildViewControllers

In the iOS 5.0 Simulator both respond which is correct behavior.

2011-11-18 09:59:31.250 testViewFunctionality[932:f803] YES addChildViewController:
2011-11-18 09:59:31.252 testViewFunctionality[932:f803] YES automaticallyForwardAppearanceAndRotationMethodsToChildViewControllers

I'm using XCode 4.2 on Lion. When I look through UIViewController.h on the 4.3 Simulator's framework there is no mention of addChildViewController: or automaticallyForwardAppearanceAndRotationMethodsToChildViewControllers but the only SDK included is 5.0.

I suppose that if you wanted to be cautious you could test the running iOS version on the running device. See How to check iOS version?