Cannot initialise GameScene more than once using SpriteKit in Swift - ios

Question

I am trying to reset my game to the start screen every time this function is called by just creating a new scene:
func restart() {
let newScene = GameScene(size: view!.bounds.size)
newScene.scaleMode = .AspectFill
view!.presentScene(newScene)
}
The first time it is called, it works correctly. However, the second time it is called I get an (apparently very common) error:
fatal error: unexpectedly found nil while unwrapping an Optional value
I don't understand why I recieve this error in this scenario.
Is there a better way to reload the entire GameScene? Do I need to do anything with the old discarded GameScene instance?

Answer 1

You have probably defined this method inside your GameScene class, right?
Let's see what the API doc says about the view property of SKScene.
The view that is currently presenting the scene. (read-only) To
present a scene, you call the presentScene: method or
presentScene:transition: method on the SKView class. If the scene is
not currently presented, this property holds nil.
So I guess you are calling this method after the current scene has been removed from the view.
Is there a better way to reload the entire GameScene?
This approach is right, but you should call restart before the current scene has been removed from the view, otherwise it has no reference to your view.
Do I need to do anything with the old discarded GameScene instance?
Nope.
Once you replace the current scene with the new one, if you don't have strong references to the old scene, ARC does remove it from memory.
To be sure the current scene is being removed you have several easy tools:
1. Debug Navigator
While the game is running take a look ⌘ + 6 at the Debug Navigator in Xcode, then invoke restart several times.
If the used memory indicator grows up, then probably you are not releasing the GameScene from memory (or some other object).
Not releasing the GameScene is one of the worst thing that can happen in a videogame because a scene holds references (directly or indirectly) to every other node in you current level/screen. It happened during the development of my game so I know what I'm talking about :D
2. deinit
Add the deinit method to you GameScene
class GameScene : SKScene {
deinit {
print("The GameScene has been removed from memory")
}
}
deinit is automatically called when the object is removed from memory. Now each time you restart your scene, you should see the message
The GameScene has been removed from memory
on the console coming from the dead scene.