Question

This example is taken from The Big Nerd Range iPhone book (page 143/144) – ItemsViewController is a subclass of UITableViewController:

@interface HomepwnerAppDelegate : NSObject <UIApplicationDelegate>
{
    UIWindow *window;
    ITemsViewController* itemsViewController;
}

....
itemsViewController = [[ItemsViewController alloc] init];
[window setRootViewController: itemsViewController]

My question is why is it necessary to have the iVar itemsViewController, why not just do this instead:

...
window.rootViewController = [[ItemsViewController alloc] init];

I presume the window will destroy its rootViewController when the app exits and thus there’s no leaks, and the window will be in existence for the lifetime of the app so I don’t understand why this and many other example have a separate iVar for the root controller?

TIA

Answer 1

The biggest advantage is simply that you can access the methods of your view controller without needing to cast over and over again:

[itemsViewController doSomething];
// vs.
[(ItemsViewController *)window.rootViewController doSomething];

Depending on the app you might need to refer to the root view controller frequently from the app delegate, for example when implementing the handlers for entering background/foreground and similar app delegate callbacks.