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What is the unarchiveFromFile method for in a GameViewController?

When I tried to add different scenes to my game in Swift, I came across the unarchiveFromFile method. The problem with this method is that it only works with the GameScene class. If you call it from

extension SKNode {
    class func unarchiveFromFile(file : NSString) -> SKNode? {
        if let path = NSBundle.mainBundle().pathForResource(file, ofType: "sks") {
            var sceneData = NSData.dataWithContentsOfFile(path, options: .DataReadingMappedIfSafe, error: nil)
            var archiver = NSKeyedUnarchiver(forReadingWithData: sceneData)

            archiver.setClass(self.classForKeyedUnarchiver(), forClassName: "SKScene")
            let scene = archiver.decodeObjectForKey(NSKeyedArchiveRootObjectKey) as GameScene 
            archiver.finishDecoding()
            return scene
        } else {
            return nil
        }
    }
}

class GameViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        if let scene = GameScene.unarchiveFromFile("GameScene") as? GameScene {
             let skView = self.view as SKView
             skView.ignoresSiblingOrder = true
             skView.presentScene(scene)
        }
        // This won't work for MenuScene.unarchiveFromFile("MenuScene") as? MenuScene
        // nor MenuScene.unarchiveFromFile("MenuScene") as? GameScene

To be able to work with other SKScenes, I changed all occurrences of the GameScene class in SKScene. While it works with other SKScene classes, I still don't understand what it is.

What is this method for? should i store it?

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2 answers

I have not used Xcode 6 a lot, but here is my understanding (someone can fix me or set out):

.. GameScene ( SKScene). GameScene.sks Project Navigator, GameScene.

, . GameScene , , ..

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0x141E, unarchiveFromFile, generics, SKS SKScene

extension SKNode {
    class func unarchiveFromFile<T:SKScene>(file : NSString) -> T? {
        if let path = NSBundle.mainBundle().pathForResource(file, ofType: "sks") {
            var sceneData = NSData(contentsOfFile: path, options: .DataReadingMappedIfSafe, error: nil)!
            var archiver = NSKeyedUnarchiver(forReadingWithData: sceneData)

            archiver.setClass(self.classForKeyedUnarchiver(), forClassName: "SKScene")
            let scene = archiver.decodeObjectForKey(NSKeyedArchiveRootObjectKey) as T
            archiver.finishDecoding()
            return scene
        } else {
            return nil
        }
    }
}

, , ,

if let scene = GameScene.unarchiveFromFile("Level1Scene") as? GameScene {
...

if let scene = GameScene.unarchiveFromFile("Level2Scene") as? GameScene {
...
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