Need help understanding new Xcode 4.2 Master-Detail Application Template - uinavigationcontroller

Question

I'm having some trouble understanding how all the "nuts and bolts" of the Master-Detail Application template works using Xcode 4.2 (without MainWindow.xib, as well as other changes). In "AppDelegate" we have the following code:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
// Override point for customization after application launch.
MasterViewController *masterViewController = [[MasterViewController alloc] initWithNibName:#"MasterViewController" bundle:nil];
UINavigationController *masterNavigationController = [[UINavigationController alloc] initWithRootViewController:masterViewController];
DetailViewController *detailViewController = [[DetailViewController alloc] initWithNibName:#"DetailViewController" bundle:nil];
UINavigationController *detailNavigationController = [[UINavigationController alloc] initWithRootViewController:detailViewController];
self.splitViewController = [[UISplitViewController alloc] init];
self.splitViewController.delegate = detailViewController;
self.splitViewController.viewControllers = [NSArray arrayWithObjects:masterNavigationController, detailNavigationController, nil];
self.window.rootViewController = self.splitViewController;
[self.window makeKeyAndVisible];
return YES;
}
I see that the window is created programmatically instead of using the MainWindow.xib that was use in previous versions of Xcode in the beginning, as well as instantiating objects for both "Master" and "Detail" view controller classes that are provided with the template and using them for separate UINavigationControllers. Then the splitViewController property is assigned a new allocated UISplitViewController object assigning the detailViewController as the "delegate" and an array is created that contains both UINavigationControllers as "viewControllers." Then the window.rootViewController is assigned this splitViewController object.
The main questions I have are
1) Why do I need two "UINavigationControllers?" Couldn't I just create the "viewController" array using the "master" and "detail" view controllers themselves?"
2) What does it do setting the "detailViewController" as the "delegate?" What actually gets delegated?
3) And finally, if I wanted to push additional items onto the "DetailViewController" stack, would I just use the "DetailViewController" class to push using the "didSelectRow.." method, or would I need to do updates to self.splitViewController.viewControllers property instead?

Answer 1

1) Why do I need two "UINavigationControllers?" Couldn't I just create the "viewController" array using the "master" and "detail" view controllers themselves?"
You don't need. But it's a way. You have the ability to push the masterViewControlleras well as the detailViewController. Look at the layout in Storyboard. With using segue you can change the controllers on each side as you like.
2) What does it do setting the "detailViewController" as the "delegate?" What actually gets delegated?
The UISplitViewget's delegated. The detailViewController will take care of the interface changing in portrait and landscape mode. See UISplitViewDelegate in the documentation.
Showing and Hiding View Controllers
– splitViewController:shouldHideViewController:inOrientation:
– splitViewController:willHideViewController:withBarButtonItem:forPopoverController:
– splitViewController:willShowViewController:invalidatingBarButtonItem:
– splitViewController:popoverController:willPresentViewController:
3) And finally, if I wanted to push additional items onto the "DetailViewController" stack, would I just use the "DetailViewController" class to push using the "didSelectRow.." method, or would I need to do updates to self.splitViewController.viewControllers property instead?
Yes you can push in the masterViewControllerwith the tableView selection. You can push either with the new controller on the masterViewControllerstack by pushing in the
- (void)viewDidAppear:(BOOL)animated
and you can push in any way you like. You don't have to update the self.splitViewController.viewControllers property. Maybe you have to set the delegate to your new detailViewController.