Different values (nil and non-nil) for self.navigationController depending on stack location

Question

I have a UIViewController subclass that accesses self.navigationController in viewDidLoad:. Depending on where it is in the view stack, I will either get the navigationController or I will get nil.

If my stack is "RootViewController -> MyViewController", I get a valid pointer.

If my stack is "RootViewController -> AnotherViewController -> MyViewController", I get nil.

In both cases, MyViewController is being pushed onto the stack with:

[self.navigationController pushViewController:self.myViewController 
                           animated:YES];

This has me stuck, because I need to be able to push another ViewController on the stack above MyViewController, which works fine in the first case but obviously fails on the second.

Answer 1

Hi Travis, from everything I can see the UIViewController's self.navigationController is designed to always return the appropriate UINavigationController as long as the UIViewController exists within a UINavigationController's stack. This is probably one of those cases that I seem to run into myself more often than I'd like where a simple coding error is masquerading as something much more complex. In these cases I usually have good luck setting up an entirely new Xcode project with the minimal code needed to reproduce the issue and more times than not in that process I find a fix for something I overlooked that can then be easily applied in the main project. I'm sorry I can't offer more specifics but what you are describing seems to go against the design of the Cocoa Touch framework and if you can still reproduce it in a minimal Xcode project written in strict accordance with the documentation it may be a good idea to file a bug report with Apple. Hopefully though you will just find something simple you overlooked and be kicking yourself in a few minutes =)

Answer 2

Hi Travis, this is exactly the same problem I'm having. Any chance you found a solution?

update: Possible something is wrong the XIB and controller setup. I did however created a class with static variables to coordinate the navigation. Once initialized with statically in the RootViewController I can now access the navigationControl from with the static variable not with the inner tableViewController's self.navigationController.

Sigh... Still it is frustrating to not know what you are doing exactly.

Answer 3

What I usually do is subclass UIViewController and add a method to set the navigationController. There's no reason not to have this as read/write, especially considering how often Apple's classes will decide not to set the navigationController (or the parentController, for that matter) even if they are in the same stack.