How to pass scene type to a function in a generic manner?

Question

I have the following boiler plate code generated by Xcode when creating a SpriteKit + GameplayKit project:

override func viewDidLoad() {
    super.viewDidLoad()

    // Load 'GameScene.sks' as a GKScene. This provides gameplay related content
    // including entities and graphs.
    if let scene = GKScene(fileNamed: "GameScene") {

        // Get the SKScene from the loaded GKScene
        if let sceneNode = scene.rootNode as! GameScene? {

            // Copy gameplay related content over to the scene

            // Set the scale mode to scale to fit the window
            sceneNode.scaleMode = .aspectFill

            // Present the scene
            if let view = self.view as! SKView? {
                view.presentScene(sceneNode)

                view.ignoresSiblingOrder = true

                view.showsFPS = true
                view.showsNodeCount = true
            }
        }
    }
}

For testing different scenes, I would prefer to move all code after super.viewDidLoad() into a function, so that I can easily test different scenes without having to edit a lot of code.

The line that I'm getting stuck on is:

if let sceneNode = scene.rootNode as! GameScene?

I am not sure how I can pass the class type in a generic manner to a function, so instead of GameScene? , I can pass the correct scene type.

How do I do this ?

Maetschl · Answer 1 · 2020-04-19T15:45:45.280

You can use some more generic like the actual boilerplate code:

override func viewDidLoad() {
    super.viewDidLoad()

    if let view = self.view as! SKView? {
        if let scene = SKScene(fileNamed: "GameScene") {
            scene.scaleMode = .aspectFill
            view.presentScene(scene)
        }
        view.ignoresSiblingOrder = true
        view.showsFPS = true
        view.showsNodeCount = true
    }
}

If all of your scenes inherit from SKScene, you will not have trouble.

But if you really need pass Type class on function to load, you can make something like this:

func loadScene<T>(named name: String, classType: T.Type) -> T? {
    return SKScene(fileNamed: name) as? T
}

And use:

let newScene = loadScene(named: "some", classType: GameScene.self)
// newScene is Optional(GameScene) type.

Sure you can remove optional replacing T? and control the nil of load.

The problem is that GKScenes can only be loaded from files, and the class type has to be mentioned in the file... I worked around it by not using GKScene at all, but I’m still interested in my original question for purely academic reasons - how to pass a class type as parameter to a function in swift.... — Rahul Iyer, Apr 19 '20 at 15:38

How to pass scene type to a function in a generic manner?

1 Answers1