I've been writing a game that has a subclass of the SKSpriteNode with some extra functions and variables. I'd like to set some of the variables when the object is created eg
let mySprite = MySubclass (width: 24, height 33)
I'm not sure this is possible which means I'll probably have to call a methos of the subclass to set the vars in a separate stage which is a bit clunky:
let mySprite = MySubclass ()
mySprite.setSize(24, height: 33)
Any ideas how I can do this in a more elegant way?
Many Thanks,
Kw
This is very fundamental OOP. Here is how you do it in Swift:
class MySubClass: SKSpriteNode {
var width: CGFloat // Declare your own properties
var height: CGFloat // ...
init(width: CGFloat, height: CGFloat) {
self.width = width // set up your own properties
self.height = height // ...
super.init() // call up to the super-class's init to set up its properties
}
}
Have you read Apple's book The Swift Programming Language? It's free and clearly covers this...
Related
TL;DR:
I want a protocol to provide default init behavior, but the compiler resists adopters adding more stored properties. I solved this with composition instead of inheritance, but what's wrong with my original approach?
Motivation
I want to automate the transformation of objects from design specifications to runtime specs. I use the example of scaling a CGSize but the intent is more general than just geometric layout. (IOW e.g. my solution won't be to adopt/reject/rewrite autolayout.)
Code
You can paste this right into a Playground, and it will run correctly.
protocol Transformable {
var size : CGSize { get } // Will be set automatically;
static var DESIGN_SPEC : CGSize { get } // could be any type.
init(size: CGSize) // Extension will require this.
}
// A simple example of transforming.
func transform(_ s: CGSize) -> CGSize {
CGSize(width: s.width/2, height: s.height/2)
}
// Add some default behavior.
// Am I sinning to want to inherit implementation?
extension Transformable {
init() { self.init(size: transform(Self.DESIGN_SPEC)) }
// User gets instance with design already transformed. No muss, fuss.
}
// Adopt the protocol...
struct T : Transformable {
let size: CGSize
static let DESIGN_SPEC = CGSize(width: 10, height: 10)
}
// ...and use it.
let t = T()
t.size // We get (5,5) as expected.
But every Eden must have its snake. I want a Transformable with another property:
struct T2 : Transformable {
// As before.
let size: CGSize
static let DESIGN_SPEC = CGSize(width: 10, height: 10)
let i : Int // This causes all sorts of trouble.
}
Whaa? Type 'T2' does not conform to protocol 'Transformable'
We have lost the synthesized initializer that sets the size member.
So... we put it back:
struct T3 : Transformable {
// As before.
let size: CGSize
static let DESIGN_SPEC = CGSize(width: 10, height: 10)
let i : Int
init(size: CGSize) {
self.size = size
self.i = 0 // But this is a hard-coded value.
}
}
But now our new member is statically determined. So we try adding another initializer:
struct T4 : Transformable {
// As before.
let size: CGSize
static let DESIGN_SPEC = CGSize(width: 10, height: 10)
let i : Int
init(size: CGSize) { self.size = size ; self.i = 0 }
// Try setting 'i':
init(i: Int) {
self.init() // Get the design spec properly transformed.
self.i = i // 'let' property 'i' may not be initialized directly;
} // use "self.init(...)" or "self = ..." instead
}
Declaring i as var shuts the compiler up. But i is immutable, and I want i that way. Explain to me why what I want is so wrong... This page is too small to include all the variations I tried, but perhaps I have missed the simple answer.
I'm new to Swift, and I'm still trying to get my head around many things. I made a class for a Meteorite:
class Meteorite {
var width: Int,
height: Int,
x: Int,
y : Int
init(width: Int, height: Int, x: Int, y: Int) {
self.width = width
self.height = height
self.x = x
self.y = y
let image = UIImage(named: "square")
let imageView = UIImageView(image: image!)
imageView.frame = CGRect(x: self.x, y: self.y, width: self.width, height: self.height)
view.addSubview(imageView)
}
}
... And I'm trying to make the meteors appear through UIImage View elements. However, on the line: view.addSubview(imageView)
I keep getting thrown the error:
Instance member 'view' cannot be used on type 'ViewController'
I might be doing this wrong, but this class is defined within the ViewController class, which is a subclass of UIViewController. I can't find anything that makes much sense to my situation online. Help is greatly appreciated :)
Meteorite may be nested within a UIViewController subclass, but you are still referencing a view property within the context of the Meteorite class. Essentially, you are sending a message to a variable that doesn't exist.
The thing to do here is to move any manipulation of the view hierarchy outside of the init for an element. This should be handled by the view controller, not the subview.
I would suggest configuring the Meteorite object in it's init, but adding it to the view controller's view within, say the viewDidLoad: method of the view controller.
I want to create a SKShapeNode at a higher level than the touchesBegan of a SpriteNode so when I want to add the SKShapeNode to the screen from the touchesBegun event on this sprite, the shape already exists, and I simply add it to the screen from within the touchesBegan override.
TL;DR, in my SKSpriteNode, I'm trying to pre-build the SKShapeNode that will be used as an animated ring when the Sprite is touched.
I'd like to create the SKShapeNode with variable/constants, so I can easily edit its values...
So in the root of the subclass I have variables for color, size, and linewidth, ready to be used in the creation of the SKShapeNode...
class Balls: SKSpriteNode {
var ringSize: CGFloat = 64
var ringColor: SKColor = SKColor.white
var ringWidth: CGFloat = 16
....
Further down, but still at the root of the class, I create my ring:
let ring = SKShapeNode(circleOfRadius: ringSize)
And am instantly greeted with the lovingly cryptic:
Can not use instance member 'ringSize' within property initializer,
property initializers run before 'self' is available.
Fine. Ok. I get it. You want to think that a functional call to a class to create a property should be done before values are assigned to self. Neither here nor there, I think I'm getting cunning and can get around that by wrapping everything in a function:
class Balls: SKSpriteNode {
var ringSize: CGFloat = 64
var ringColor: SKColor = SKColor.white
var ringWidth: CGFloat = 16
var myRing = SKShapeNode()
func createRing() -> SKShapeNode{
let ring = SKShapeNode(circleOfRadius: ringSize)
ring.strokeColor = ringColor
ring.lineWidth = ringWidth
return ring
}
This generates no errors, and my excitement builds.
So I add another line, to create the actual ring:
....
myRing = createRing()
Dead again:
! Expected
declaration
I have absolutely no idea what this means and began to randomly attempt weird things.
One of them is heading into my already messy convenience initializer and adding myRing = createRing() in there... and this WORKS!
How and why does this work, and is this the best/right/proper way to be circling the drain of initialization?
:: EDIT:: UPDATE :: Full Code Context ::
Here's the full class with my bizarre and misunderstood initialisers.
import SpriteKit
class Circle: SKSpriteNode {
var ringSize: CGFloat = 96
var ringColor: SKColor = SKColor.white
var ringWidth: CGFloat = 8
var myRing = SKShapeNode()
override init(texture: SKTexture?, color: UIColor, size: CGSize) {
super.init(texture: texture, color: color, size: size)
}
convenience init() {
self.init(color: SKColor.clear, size: CGSize(width: 100, height: 100))
myRing = createRing()
addChild(myRing)
print("I'm on the screen")
explodeGroup = create_explosionActionGroup()
}
convenience init(color: UIColor, size: CGSize, position: CGPoint) {
self.init(color: color, size: size)
self.position = position
myRing = createRing()
explodeGroup = create_explosionActionGroup()
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
func createRing() -> SKShapeNode{
let ring = SKShapeNode(circleOfRadius: ringSize)
ring.strokeColor = ringColor
ring.lineWidth = ringWidth
return ring
}
Your createRing() method is inside Ball class so you need to create an instance of Ball first.
Simple way - You can change creation of instance to
let ball = Balls()
let myRing = ball.createRing()
I'm slightly confused as to where you placed the
myRing = createRing()
line of code but I'm wondering if this setup would help solve your problem
lazy var myRing: SKShapeNode = {
let ring = SKShapeNode(circleOfRadius: ringSize)
ring.strokeColor = ringColor
ring.lineWidth = ringWidth
return ring
}()
This way myRing would be created when it was accessed which should be after the Balls class is instantiated which would mean that ringSize, ringColor and ringWidth would all exist.
Based on your update I think your best bet might be to just make your three ring variables ‘static let’ instead. That way they will exist and have the set value before initializing the main class. The errors you’re seeing are because you created instance variables. Those will only exist when the instance has been initialized. So if you tried to call the ring method as the declaration of the variable or if you did it within the init before self/super init is called then the instance variables wouldn’t be accessible. The most recent code you’ve added should be working because you create the instance before attempting to generate the ring. I hope that makes sense and helps.
And am instantly greeted with the lovingly cryptic:
Can not use instance member 'ringSize' within property initializer, property initializers run before 'self' is available.
So one way around this problem would be to make the default ringSize available another way, e.g.
static let defaultRingSize: CGFloat = 64
var ringSize: CGFloat = Circle.defaultRingSize
let ring = SKShapeNode(circleOfRadius: Circle.defaultRingSize)
... but I question why you even have a var ringSize property like that. Shouldn't you have a didSet observer on it, so that if you change its value, you can update the shape of ring?
Dead again:
! Expected declaration
You weren't clear, in your question, how you actually triggered this, but I guess you tried something like this:
class Circle: SKSpriteNode {
var ringSize: CGFloat = 96
var myRing = SKShapeNode()
myRing = createRing() // “Expected declaration” error on this line
The problem here is that you've placed a statement in the body of your class, but only declarations are allowed in the body.
One of them is heading into my already messy convenience initializer and adding myRing = createRing() in there... and this WORKS!
How and why does this work
All of your class's own instance variables must be initialized before a super.init call. Since myRing has a default value, the compiler effectively inserts the initialization of myRing before the call to super.init in your designated initializer, like this:
override init(texture: SKTexture?, color: UIColor, size: CGSize) {
// Compiler-inserted initialization of myRing to the default
// value you specified:
myRing = SKShapeNode()
super.init(texture: texture, color: color, size: size)
}
Since you declared var myRing, you can then change it later to the customized SKShapeNode you really want.
is this the best/right/proper way to be circling the drain of initialization?
Well, “circling the drain” means “failing”, so I guess you're asking if this is “the best/right/proper way” to fail at initialization… I suppose it's not the best way to fail, since you didn't actually fail in the end.
Or maybe you meant “I hate the way Swift does initialization so I'm going to throw some shade”, in which case, you ain't seen nothin' yet.
But maybe you really meant “is this the best/right/proper way to initialize my instance”, in which case, well, “best” and “right” and “proper” are pretty subjective.
But I can objectively point out that you're creating an SKShapeNode (as the default value of myRing) just to immediately throw it away and create another SKShapeNode. So that's a waste. You've also got calls to createRing in both of your convenience initializers, but you could factor them out into the designated initializer.
But I wouldn't even do it quite like that. SKShapeNode's path property is settable, so you can just create a default SKShapeNode and then change its path after the call to super.init. That also makes it easier to handle changes to ringSize and the other properties, because you can funnel all the changes through a single method that knows how to make myRing match the properties.
Here's how I'd probably write your class:
import SpriteKit
class Circle: SKSpriteNode {
var ringSize: CGFloat = 96 {
// Use an observer to update myRing if this changes.
didSet { configureMyRing() }
}
var ringColor = SKColor.white {
didSet { configureMyRing() }
}
var ringWidth: CGFloat = 8 {
didSet { configureMyRing() }
}
// This can be a let instead of a var because I'm never going to
// set it to a different object. Note that I'm not bothering to
// initialize myRing's path or any other property here, because
// I can just call configureMyRing in my init (after the call to
// super.init).
let myRing = SKShapeNode()
override init(texture: SKTexture?, color: SKColor, size: CGSize) {
super.init(texture: texture, color: color, size: size)
// Call this now to set up myRing's path and other properties.
configureMyRing()
}
convenience init() {
self.init(color: SKColor.clear, size: CGSize(width: 100, height: 100))
// No need to do anything to myRing now, because my designated
// initializer set it up completely.
addChild(myRing)
print("I'm on the screen")
// Commented out because you didn't provide this property
// or method in your question.
// explodeGroup = create_explosionActionGroup()
}
convenience init(color: SKColor, size: CGSize, position: CGPoint) {
self.init(color: color, size: size)
self.position = position
// Commented out because you didn't provide this property
// or method in your question.
// explodeGroup = create_explosionActionGroup()
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
private func configureMyRing() {
myRing.path = CGPath(ellipseIn: CGRect(x: -ringSize / 2, y: -ringSize / 2, width: ringSize, height: ringSize), transform: nil)
myRing.strokeColor = ringColor
myRing.lineWidth = ringWidth
}
}
If I create an instance of the class below and call the spawn function from my controller, the sprite will appear but I won't be able to change any of its properties.
class Hero: SKSpriteNode
{
var hero = SKSpriteNode(imageNamed: "hero3")
func spawn(parentNode: SKNode, position: CGPoint, size: CGSize = CGSize(width: 50, height: 50))
{
hero.size = size
hero.position = position
hero.physicsBody = SKPhysicsBody(circleOfRadius: 25)
hero.physicsBody?.allowsRotation = false
hero.zPosition = 10
parentNode.addChild(hero)
}
}
If I get rid of the hero property and change everything to self, it works fine.
class Hero: SKSpriteNode
{
func spawn(parentNode: SKNode, position: CGPoint, size:CGSize = CGSize(width: 50, height: 50))
{
self.size = size
self.position = position
self.texture = SKTexture(imageNamed: "hero3")
self.physicsBody = SKPhysicsBody(circleOfRadius: 25)
self.physicsBody?.allowsRotation = false
self.zPosition = 10
parentNode.addChild(self)
}
}
I'm sure this is swift 101, but can someone please explain why the first version doesn't work as expected?
In your first example, you created a var (basically a SpriteNode inside the SpriteNode).
When you instantiate the class like let hero = Hero(....) you now have a SpriteNode called hero, with a property called hero. You can change either. Calling hero.size would change the base hero, and hero.hero.size would change the inside SpriteNode....this is probably not the behavior you were looking for.
The second class looks correct, if you are just trying to create a SpriteNode and modify it. The class is a subclass of SpritNode, so it's already a SpriteNode - no need to create one inside it like the first one.
Hope this helps!
Your Hero class inherits from SKSpriteNode, so it is essentially an SKSpriteNode already, which means you don't need to create a hero SKSpriteNode variable.
In your first class, when you use hero.size = size, you're accessing the properties of the variable within your class instead of on the class itself. Then you add the hero SKSpriteNode as a child along with all its properties, but your class SKSpriteNode, which holds the variable doesn't have set properties size or a physics body. You can think of the class as a container that's holding the variable SKSpriteNode.
In your second function, when you use self.size = size, you're accessing the class's properties and giving the class SKSpriteNode all the properties you need to use it in other classes.
Basically, I have an SKScene class called GameScene. In GameScene, I have a variable called playableArea that is calculated depending on the size of the user's phone.
I have an enemy class that needs to know the width of the playableArea, and then use that value to move to to the x position by an SKAction depending on the width of playableArea.
This is my class (simplified version):
class PacuPiranha: Fish {
static var s = SKSpriteNode(imageNamed: "PacuPiranha1")
var width: CGFloat = 0
struct SharedAssets {
static var move: SKAction!
static var token: dispatch_once_t = 0
}
init(position: CGPoint, width: CGFloat) {
self.width = width
}
override class func preloadAssets() -> SKTexture? {
dispatch_once(&SharedAssets.token, {
SharedAssets.move = SKAction.sequence([SKAction.moveToX(width + s.size.width, duration: 2.5), SKAction.removeFromParent()])
return SharedAssets.texture
}
}
}
The enemy fish needs to move to the other size of the screen, but the size of the screen is determined by the size of the device the user is using, so I need to pass the width of the screen to the moveToX action which occurs in the init call. But I get the error "Instance member 'width' cannot be used on type 'PacuPiranha'."
How do I get the width of a variable that is from the GameScene class, which is where the new object of the enemy is being created?
let fish = PacuPiranha(position: CGPoint(...), width: playableArea.size.width)
I have also tried making a new function in the enemy class like this:
func getWidth() -> CGFloat {
let view = scene as! GameScene
view.playableArea.size.width
}
And then using getWidth() inside the moveToX, but that didn't work either since it's asking for an argument of type self: PacuPiranha.
Retrieving the Screen Size
You can get the screen size with this code
let screenSize = UIScreen.mainScreen().bounds.size
My point of view
I think you are overcomplicating the code.
Wouldn't it be easier if PacuPiranha was a subclass of SKSpriteNode added to GameScene?
And finally, do you really need all that code to preload the resources? SpriteKit is pretty good at managing the resources, you should let it do its work unless your game specifically needs a custom approach.
Update
IF PacuPiranha was a SKSpriteNode subclass (as it should be) added to the the SKScene you would be able to use this code to get the size of the current view.
class PacuPiranha: SKSpriteNode {
func foo() {
if let viewSize = self.scene?.view?.frame {
print(viewSize)
}
}
}
UIScreen.mainScreen().bounds.size.width * UIScreen.mainScreen().scale Will give you the screens width in pixels.