Why isn't view available? - swift

Question

Why do I get:
fatal error: unexpectedly found nil while unwrapping an Optional value
while switching to the next scene and back?
// Main Menu Scene
class MainMenuScene: SKScene {
override func didMoveToView(view: SKView) {
// self.backgroundColor = UIColor.whiteColor()
var timer = NSTimer.scheduledTimerWithTimeInterval(5.0, target: self, selector: "switchScene", userInfo: nil, repeats: true)
println("loaded MainMenuScene")
}
override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {
for touch: AnyObject in touches {
let location = touch.locationInNode(self)
}
}
func switchScene() {
println("switching to GameScene")
var game = GameScene(size: CGSizeMake(2048, 1536))
game.scaleMode = .AspectFill
if self.view == nil {
println("no self.view")
} else {
self.view!.presentScene(game)
}
}
}
// Game Scene
class GameScene: SKScene {
override func didMoveToView(view: SKView) {
// self.backgroundColor = UIColor.whiteColor()
var timer = NSTimer.scheduledTimerWithTimeInterval(5.0, target: self, selector: "switchScene", userInfo: nil, repeats: true)
}
override func touchesBegan(touches: NSSet, withEvent event: UIEvent) {
/* Called when a touch begins */
for touch: AnyObject in touches {
let location = touch.locationInNode(self)
}
}
func switchScene() {
// make var a member variable or this won't work
timer.invalidate()
var menu = MainMenuScene(size: CGSizeMake(2048, 1536))
menu.scaleMode = .AspectFill
self.view!.presentScene(menu)
}
}
First, change timer variable to a member.
Second, invalidate the timer.
Everything runs as expected.

Answer 1

From the SKScene docs:
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.
view is nil because the your GameScene (self) is not currently presented when this code runs. Your app crashes because you are force-unwrapping something that's nil.

Answer 2

Actually, Aaron was right. If you put remove the timer, or don't add enough time, then the view will be nil. In this instance, with the timer, by time the timer trigged, view did have a view initially.
What I was forgetting to do was invalidate() my timer before presenting the new SKScene. This kept the timer running, and when it triggers, view! is really nil because the object was removed.