Question

There’s something fundamental that I’m not understanding about presenting views that get their interface from a XIB file.

My app’s root view controller is a UITabBarController. One of the tab bar options presents a UINavigationController-controlled view. One the navigation bar of that view, I have a plus (+) button for adding a new item. I want to present the AddItem view as a modal view, and it should take its interface from the AddItemView.xib file. That XIB file has in it a Navigation Controller.

However, the navigation bar doesn’t appear. Here’s the function that gets called when clicking on that plus button:

- (void)showNewView:(UIViewController *)viewController
{
    AddItemViewController *vc = [[AddItemViewController alloc] initWithNibName:@"AddItemViewController" bundle:nil];

//viewController is the UIViewController on which the plus button was tapped
    [viewController.navigationController presentModalViewController:vc animated:NO];
}

All I get is a white screen. Do I need to do something in viewDidLoad for AddItemViewController? Do I need to connect something to the UINavigationController instance in the XIB?

All this seems to just work with the tab bar, which is in the MainWindow.xib file. The UITabBarController there has a UINavigationController under it, which in turn has a subclass of UITableViewController under it, and that in turn contains the UITableView that is the initial content you see on the screen when tapping on the corresponding option in the tab bar. So I’m not sure why just sticking those things in IB doesn’t cause the same to happen.

As I said in the beginning, I’m sure this problem stems from a fundamental misunderstanding about the relationship between XIB files, their view controllers, and the view controllers that call upon them. So while I do want to get this particular issue solved, I’d love an answer that can address this broader misunderstanding.

Answer 1

The view controller that you’re presenting is vc, which is an AddItemViewController. It’s not enough that there’s a navigation controller in the .xib file — you have to actually use it. 😉

Check out Listing 6-1 in Presenting a View Controller Modally for an example of one way to do what you want. If you want to use the nav controller that’s already in your .xib, then make an outlet for it and present it rather than the AddItemViewController that you’re currently presenting.

All this seems to just work with the
tab bar, which is in the
MainWindow.xib file. The
UITabBarController there has a
UINavigationController under it, which
in turn has a subclass of
UITableViewController under it, and
that in turn contains the UITableView
that is the initial content…

All those objects in MainWindow.xib are loaded at the same time and already connected to each other. But you don’t have the tab bar connected directly to the table view controller, right? You have it connected to the navigation controller. When the corresponding tab is tapped, the tab bar controller doesn’t know a thing about the table view controller — it just asks that nav controller for its view, and the navigation controller then asks the table view controller for its view, layers that with the navigation views (see Anatomy of a Navigation Interface) and returns the result to the tab bar controller.

Imagine what would happen if you did connect the tab bar controller directly to the table view controller. This time, the tab bar controller would be talking to the table view controller directly, so when it asks that tab’s view controller for its view, all it gets back is the table view controller’s view, i.e. the table, with no navigation features.

The same thing is happening with your modal view controller. Since you’re presenting the AddItemViewController and not the navigation controller, the AddItemViewController is all you get.