Question

It is my understanding that every view has it’s own controller class. I know generally that the xib file is the application view/subview. My question is does the MainWindow.xib have it’s own controller and if so, where can it be found?

Answer 1

You are right in that a xib file can allow to associate a view to its view controller.

Now, MainWindow.xib contains the main UIWindow for your app (at least). UIWindow is not a UIView and does not need a UIViewController.

On the other hand, you can create any object you like inside of a MainWindow.xib, so you can also have a UIView in there, which you then add to the UIWindow instance, and its corresponding UIViewController.

If you think about additional xibs, what happens with them is that they define a UIView, and additionally also specify the File’s Owner type, which is usually UIViewController and gets instantiated by loading the xib.

In this sense, MainWindow.xib, though not requiring a UIViewController, still needs a File’s Owner, and this is the UIApplication singleton. Since you cannot modify nor derive a class from UIApplication, the way to interact with the UIWindow instance is through the UIApplication‘s delegate.

Take in mind that MainWindow.xib plays a special role, in that it is also specified in the info.plist file. You can do without one (by removing the corresponding entry from info.plist) and simply declare your application delegate when calling UIApplicationMain from main.c. In this case, nor application delegate neither the UIWindow will be instantiated through the xib mechanism; you will need to instantiate a UIWindow from you application delegate’s applicationDidFinishLaunching.