Instantiating a base class inheriting from SKSpriteNode in Swift - swift

Question

I'm trying to write a generic Alien 'blueprint' class for my first iPhone game. This class will contain a handful of properties and methods that will be inherited by all the actual alien subclasses. That said, Alien really shouldn't have a texture and shouldn't have its own set of defined values.
//Generic alien type: a blue-print of sorts
class Alien:SKSpriteNode{
let velocityVector:CGVector
let startPos:CGPoint
init(texture:SKTexture, startPosition startPos:CGPoint,moveSpeed: CGFloat,velocityVector:CGVector){
super.init(texture: texture, color: UIColor.clearColor(), size: texture.size())
self.velocityVector = normalizeVector(velocityVector)
self.position = position
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
Every time I try setting this up I run into a handful of errors such as :
"Use of instance member 'normalizeVector' on type GameScene; did you mean to use a value of type GameScene instead?"
normalizeVector is a function that is written above the Alien class (within GameScene). I'm not sure what this means, as this is a normal function within the GameScene. If I remove this bit, I still receive the error:
"Property self.velocityVector is not initialized at super.init call"
I'm confused because I had thought that super.init() was only necessary because I'm making a subclass of SKSpriteNode and that it wouldn't need to have the subclass-specific properties passed to it.
Lastly, is there a way to call super.init() without having an actual texture as this blueprint class isn't ever going to be "displayed"?
After looking through Apples Documentation on classes/initialization I'm still stuck. Any help would be great, thanks.

Answer 1

You have a couple of issues, first of all, as the error message says, you need to initialize all variables before you call super.init:
init(texture:SKTexture, startPosition startPos:CGPoint,moveSpeed: CGFloat,velocityVector:CGVector){
self.velocityVector = Alien.normalizeVector(velocityVector)
self.startPos = startPos
super.init(texture: texture, color: UIColor.clearColor(), size: texture.size())
self.position = position
}
Second, it sounds like you're defining normalizeVector in a subclass or somewhere else? What I did was to define it as a static method (since it's used before this is initialized, it can't be an instance method) and then you can use it in the init method. Put it all together and it looks like:
class Alien:SKSpriteNode {
static func normalizeVector(vector:CGVector) -> CGVector {
let len = sqrt(vector.dx * vector.dx + vector.dy * vector.dy)
return CGVector(dx:vector.dx / len, dy:vector.dy / len)
}
let velocityVector:CGVector
let startPos:CGPoint
init(texture:SKTexture, startPosition startPos:CGPoint,moveSpeed: CGFloat,velocityVector:CGVector){
self.velocityVector = Alien.normalizeVector(velocityVector)
self.startPos = startPos
super.init(texture: texture, color: UIColor.clearColor(), size: texture.size())
self.position = position
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}

Answer 2

You declared velocityVector as a non optional property so of course if your don't populate it within your initializer you get a compiler error.
This is why when you comment this line your get a compile error.
self.velocityVector = normalizeVector(velocityVector)