Get UINavigationBar delegate to allow "back", with a nice animation

Question

Scenario on an iPhone:

The user taps the back button, the UINavigationBar delegate method (implemented in a subclass of UINavigationController) returns YES, like this:

- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item
{
    // Verify stuff...

    return YES;
}

Now, according to the docs, it's the app's responsibility to keep the nav bar and the contents in sync, and the place to do that is in the delegate method

- (void)navigationBar:(UINavigationBar *)navigationBar didPopItem:(UINavigationItem *)item

The problem is, that didPopItem is only called after the nav bar's pop animation sequence is finished, so if I call [self popViewControllerAnimated: NO] there, the net result is that first the nav bar slides back, then the contents.

And that just looks wrong.

If I call the navigation controller's pop... in the delegate shouldPop... method, I get an error message to the effect that I am overlapping animations, and the final state is not clean.

So my question is, is there another way to get the UINavigationController to change contents, preferably with a nice animation in sync with the nav bar's, but without creating confusion between the nav bar and the navigation controller?

The target OS is iOS 4.2 and later.

I am aware that I could just create another left button in place of the back button, but I found it cleaner to use a delegate, plus, I get a "real" back button, which is what I want.

Answer 1

If you are using a UINavigationController, you do not need to manage this yourself. You will save yourself a lot of trouble by simply using the UINavigationController. It will take care of popping the content view along with the navigation bar items.

Answer 2

Try this:

Imagine you have viewControllerA and viewControllerB. viewControllerA is the first one and doesn't need a navigationBar and viewControllerB does.

On the method viewWillAppear in viewControllerA put the code:

[self.navigationController setNavigationBarHidden:YES animated:YES];

and when popping the viewControllerB you do so with animation. Both animations will be in sync automagically.

Don't know if this is valid for iOS4.2