When you load a UIViewController Subclass programmatically, any nib associated with that ViewController will not be loaded if you named any of the files a different name than your subclass.
The only way to load the nib automatically, without passing a string name to the initializer, is to make sure your x.nib and class.swift has the same name as the SubClass.
Is there a way around this?
According to the documentation, you actually can load a nib based view controller without naming it exactly the same thing. Although matching names is the most common way to do this, there's a second case, which should work even with Swift.
From the documentation:
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:
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.
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.