Question

I may have some misunderstanding regarding the use of the UINavigationControllerDelegate protocol. Here is my situation:

I have a ViewController, let’s call it, BViewController that may display a PopoverViewController. BViewController is the second ViewController in a NavigationContoller’s stack, after AViewController. I need to dismiss the PopoverViewController when the user hits a button in BViewController and the app takes us back to the previous view–AViewController.

To do that, I have implemented the following in BViewController

- (void)viewWillDisappear:(BOOL)animated {
    NSLog(@"BViewController will disappear");
    // Check whether the popoverViewController is visible
    if (self.popoverController.popoverVisible==YES) {
        [self.popoverController dismissPopoverAnimated:NO];
    }
}

However, that is not being called directly by the framework as BViewController is inside a NavigationController. Hence, I register a UINavigationControllerDelegate with my NavigationController and implement the following two methods:

- (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated {
    // Pass the message on to the viewController in question
    [viewController viewWillAppear:animated];
}

- (void)navigationController:(UINavigationController *)navigationController didShowViewController:(UIViewController *)viewController animated:(BOOL)animated {
    // Pass the message on to the viewController in question
    [viewController viewWillDisappear:animated];
}

However, it seems that the passed in viewController parameter in both methods is the one that is about to be shown. I would have expected that the second method gives me access to the one that is about to disappear. So, when the user hits aforementioned button viewWillDisappear gets called on AViewController (which is about to be shown) and not on BViewController (which is about to disappear). Does that sound right? The apple documentation refers in both cases to

The view controller whose view and navigation item properties are being shown.

…which is not quite clear, I think. Thank you for some help, guys.

Answer 1

The two delegate method are both called for the same action (showing a view controller). The navigationController: willShowViewController:animated: is called before the new view controller is visible in the gui. The navigationController:navigationController didShowViewController:animated: is called after the new view controller is shown.

You will find this pattern in a lot of delegate protocols from apple. Unfortunately you do not have a delegate method in the NavigationViewController which tells you if the action was a pop or push.