Link Storyboard to UIViewController with Generic

Question

I have this view controller, meant to present model object details in a generic way:

class APIModelDetailsVC<T where T: APIModel>: UIViewController {...}

I'd like my storyboard to use this class. I'm able to assign it in Interface Builder:

I do the preparation of this ViewController in a tableview's didSelect method (including specifying the type for the generic placeholder):

override func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
  print("didSelectRowAtIndexPath \(indexPath.row)")
  if let vc = UIStoryboard(name: "APIModelDetailsVC", bundle: nil).instantiateInitialViewController() as? APIModelDetailsVC<StarWarsPerson> {
    vc.model = data[indexPath.row]
    self.navigationController?.pushViewController(vc, animated: true)
  }
}

When I attempt to navigate to this view controller, I get the following console error:

Unknown class _TtC14api_collection17APIModelDetailsVC in Interface Builder file.

Is this a documented limitation with Storyboards? Is there a way I can/should specify the generic so the storyboard can link to it?

Answer 1

Storyboards have a problem with having a generic class. The thing is that Interface Builder communicates to the ViewController through the Objective-C runtime. Because of this, InterfaceBuilder is limited to the features that Objective-C provides. In this case, generics are not supported.

A workaround for this is using the .load() method of NSObject.

For example, if you have the mentioned ViewController class:

class APIModelDetailsVC<T where T: APIModel>: UIViewController {...}

You should create a "dummy" ViewController such as:

class StartWasModelDetailsVC: APIModelDetailsVC<StarWarsPerson> {...}

and set this last ViewController in the storyboard. Afterwards, in order to make this work in the Objective-c runtime, you should add the following in your AppDelegate or somewhere before this controller is loaded.

StartWasModelDetailsVC.load()

Hope it helps!