How do I get the screen dimensions before init()? - swift

Question

I'm making a small game in swift and want to make my player move across 3 fixed points on the screen.
I created an array to store the values in which I calculate in the init function, but the compiler doesn't agree with me not declaring the array before super.init(). Here's what I have
//properties
var player:SKSpriteNode = SKSpriteNode()
var playerPos = 1
var legalPositions: [CGFloat]
override init(size:CGSize)
{
super.init(size: size)
legalPositions[0] = self.frame.width/4
legalPositions[0] = self.frame.width/2
legalPositions[0] = self.frame.width/0.5
}
When I try to build it I get the error
GameScene.swift:31:9: Property 'self.legalPositions' not initialized at super.init call
Is there a way to initialize the property before calling the init function?

Answer 1

This is actually a good use case for Implicitly Unwrapped Optionals. Basically you'd define legalPositions as [CGFloat]! which will default it to nil. Then you can set it after your call to super.init(size: size).
Since it's implicitly unwrapped, you don't have to worry about unwrapping it with optional binding or forced unwrapping each time you use it. And, since you're always setting it in your init method, you don't have to worry about it being nil and causing a crash.
//properties
var player:SKSpriteNode = SKSpriteNode()
var playerPos = 1
var legalPositions: [CGFloat]!
override init(size:CGSize)
{
super.init(size: size)
legalPositions[0] = self.frame.width/4
legalPositions[0] = self.frame.width/2
legalPositions[0] = self.frame.width/0.5
}

Answer 2

Yes, you can use a dummy value that gets overwritten in the initializer:
var legalPositions: [CGFloat] = [0]
That way, the legalPositions array is initialized before you're calling the base class initializer. Swift's two-phase initialization requires this process in order to be able to guarantee that all properties are initialized after creating a new instance of a class.
The benefit of this approach is that there's no need for implicitly unwrapped optionals. They open up the possibility for nil values being set, which is not what you want.
Note that the first two assignments in your snippet are unnecessary since the third one will overwrite the value of the first item of the legalPositions array anyway.