Question

I have a weird question:
What is the pattern that the UIKit is using to figure out the right nib name for a UIViewController, when you don’t explicitly specify the nibName?

Why am I asking?

Because I thought (With a good reason) that the system will first look for the nib with the same name as the controller’s class’s.
That is, if I have a VideoViewController, the system will first look for VideoViewController.xib.

Apparently this is not the case.
I have another class, VideoView, which is a subclass of UIView. I have a nib called VideoView.xib that contains all the view hierarchy for VideoView.

When I try to run the app, it crashes immediately with setValue:ForUndefinedKey Exception.
I noticed that the key is always a key from the VideoView.xib, and not from VideoViewController.xib. That means that the system is trying to load VideoView.xib for a view controller named VideoViewController.

It seems that if the system will find a nib with a name similar the controller class name -only without the “Controller” suffix, it’ll use that nib.

I confirmed it by renaming my class to VideosViewController (With ‘s’), and everything worked just fine.

Are there any more edge conditions like this one?
Or is there a place that specify the exact algorithm?

It took me an hour to debug this one, and I don’t want to waste any more time in the future on the same problem…

Thanks!

Answer 1

From the documentation of UIViewController.nibName property:

If you use a nib file to store your view controller’s view, it is
recommended that you specify that nib file explicitly when
initializing your view controller. However, if you do not specify a
nib name, and do not override the loadView method in your custom
subclass, the view controller searches for a nib file using other
means. Specifically, it looks for a nib file with an appropriate name
(without the .nib extension) and loads that nib file whenever its view
is requested. Specifically, it looks (in order) for a nib file with
one of the following names:

1. If the view controller class name ends with the word “Controller”, as
   in MyViewController, it looks for a nib file whose name matches the
   class name without the word “Controller”, as in MyView.nib.
2. It looks
   for a nib file whose name matches the name of the view controller
   class. For example, if the class name is MyViewController, it looks
   for a MyViewController.nib file.