Can we use a nested class for IBDesignable?

Question

I am developing a graphic library in Swift. The code cannot be shared, but I made a sample here (see the button example, Radio buttons were dedicated to another question).

I would like to have a namespace MyGraphicLibrary for my components: MyGraphicLibrary.Button instead of MyGraphicLibraryButton

The sample pod has two classes:

// Independent class
@IBDesignable public class CustomButton: UIButton {
    ...
}

// Namespace for my components
public class MyGraphicLibrary: NSObject {

}

// Namespaced button
public extension MyGraphicLibrary {
    @objc(MyGraphicLibraryButton) @IBDesignable class Button: UIButton {
        ...
    }
}

The CustomButton class is behaving as expected in the interface builder: I can easily add the custom class to the button (see Main.storyboard).

For the nested class, it is not possible to set it with its normal name (Button or MyGraphicLibrary.Button).

The only way is to set the class @objc name MyGraphicLibraryButton; there is no autocompletion and the module must be set to none (which looks like a nonsense, the class belongs to the GraphicLibrary module). Removing the @objc name makes no difference.

Is there a way to make the nested class be handled correctly by the Interface Builder?

Answer 1

I think, in general, the answer to your question is "No" you cannot use Objective-C classes in the way you are trying to.

Interface Builder is looking for an Objective-C Class name in it's interface. Objective-C presents a flat space for class names. There is no concept of a nested namespace (which is why you end up with name prefixes like 'NS')

You are trying to impose a namespace structure using features of Swift, but that structure has no meaning to Objective-C. Even if you declare an Objective-C class in a nested Swift context, its still going to exist in the flat space of Objective-C classes.

And Interface Builder is going to pull the name from that flat space.