How do I avoid hard coding values? - ios

Question

In my application, I have items randomly popping up from the bottom of the screen. The way I set my code forced me to use hard coded values for x-position from where the items are popping up. Instead of those x-positions being hard coded, I want to change them to for instance GameScene.size.width / 4, so that the application's game play stays the same for all devices. Here is how I set up my code:
class Items{
var node = SKNode()
var item1 = SKSpriteNode(imageNamed: "CY")
var item2 = SKSpriteNode(imageNamed: "SY")
var item3 = SKSpriteNode(imageNamed: "PY")
var velocity = CGPoint.zero
var positionOffset = CGFloat(0)
var minVelocity = CGFloat(200)
init(pOffset: CGFloat) {
positionOffset = pOffset
node.zPosition = 1
node.addChild(item1)
node.addChild(item2)
node.addChild(item3)
node.hidden = true
}
....
class GameWorld{
var size = CGSize()
var node = SKNode()
var can1 = Items(pOffset: 208) //this is what is deciding the position
var can2 = Items(pOffset: 620)
init() {
node.addChild(can1.node)
node.addChild(can2.node)
}
....
The offset line in GameWorld class is what is deciding the position. What can I change in order to be able to say "GameScene.size.width / 4" for can 1 and similarly the same for can2 and not have an issue? I did try different ways to get it to work, but nothing seems to go my way. When I'm able to say GameScene.size.width / 4, for some reason, the app launches, but none of the gameplay loads up. Any help will be greatly appreciated.
Here is my GameScene Class:
class GameScene: SKScene {
... // added sprites but erased the code for now for space purposes
var touchLocation = CGPoint(x: 0, y: 0)
var nrTouches = 0
var rightTap: Bool = false
var leftTap: Bool = false
var delta: NSTimeInterval = 1/60
static var world = GameWorld()
override init(size: CGSize) {
super.init(size: size)
GameScene.world.size = size
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
override func didMoveToView(view: SKView) {
backgroundColor = UIColor.whiteColor()
let pos1 = CGPoint(x: size.width / 1.333, y: size.height / 1.1)
addChild(GameScene.world.node)
delta = NSTimeInterval(view.frameInterval) / 60
sprite1.position = pos1
sprite2.position = pos1
sprite3.position = pos1
sprite1.zPosition = 2
sprite2.zPosition = 2
sprite3.zPosition = 2
sprite2.hidden = true
sprite3.hidden = true
addChild(sprite1)
addChild(sprite2)
addChild(sprite3)
}
.....
Edit: added GameScene Class

Answer 1

For this scenario, you cannot declare:
var can1 = Items(pOffset: 208)
var can2 = Items(pOffset: 620)
The way you are doing it now. This is because at compile time, the game has no idea what the screen size is. Instead do not initialize the variable, just declare it like this:
var can1 : Items!
var can2 : Items!
Then this next part is tricky, if you are doing auto layouts, you need to make sure that the view is already created and sized before you present your scene. This does't happen till somewhere around viewDidAppear in the view controller
In your scenes didMoveToView, initialize your variables:
override func didMoveToView(view : SKView)
{
... //super and other code
can1 = Items(pOffset: view.frame.size.width/4)
can2 = Items(pOffset: view.frame.size.width/2)
}