Swift Unable to Override Variables in Subclass

Question

I am working on a macOS project in Swift, and I've been having a lot of trouble with overriding variables in a few classes I've made. In classTwo Xcode is presenting the error Cannot override with a stored property 'texture' on the line;

override var texture: SKTexture?

This is a bit of the code I'm using.

     public class classOne: SKSpriteNode {

        required public init?(coder aDecoder: NSCoder) {
            fatalError("init(coder:) has not been implemented")
        }
// Other functions
    }

And the second class;

    class classTwo: classOne {
        override var texture: SKTexture? // Cannot override with a stored property 'texture'

        required init?(coder aDecoder: NSCoder) {
            fatalError("init(coder:) has not been implemented")
        }
// Some other functions
    }

I do plan to actually define a specific texture for classTwo, but for now I couldn't even make this work.. Thanks in advance, and I'd appreciate any help on solving this issue!

Possible duplicate of [Swift override instance variables](https://stackoverflow.com/questions/26188903/swift-override-instance-variables) — Arthur Sahakyan, Jun 30 '17 at 14:39
Is it even possible? SpriteKit is a framework by Apple, so I'd reckon this kind of overriding wouldn't be possible — Lior Pollak, Jun 30 '17 at 14:45
I don't understand what you mean, UIView is also apple class ... — Arthur Sahakyan, Jun 30 '17 at 14:49
https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Inheritance.html and search for `super.` include `.` in your search and read through... — mfaani, Jan 31 '20 at 16:54

Lawliet · Accepted Answer · 2017-07-01T00:10:56.650

4

EDIT

@Knight0fDragon was right, a better approach is to use super.texture

class classTwo: classOne {
    override var texture:SKTexture? {
        get {
            return super.texture
        }
        set {
            super.texture = newValue
        }
    }            
}

In order to override the property you need to initialise it. In other words, giving it an initial value. If you don't want, here is a workaround:

class classTwo: classOne {    
    var _texture:SKTexture
    override public var texture: SKTexture? {
        get {
            return _texture
        }
        set {
            _texture = newValue!
        }
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    // Some other functions
}

edited Jul 01 '17 at 00:10

answered Jun 30 '17 at 14:46

Lawliet

3,438
2
17
28

1

This is not recommended, there may be a case where something in SKSpriteNode may access texture via the stored variable, not the property, thus giving an undesired result – Knight0fDragon Jun 30 '17 at 18:17
use super.texture instead – Knight0fDragon Jun 30 '17 at 18:17
Thank you @Lawiet, @Knight0fDragon! I’ll try to implement this code and let you know on how it go goes. – Jake3231 Jul 01 '17 at 14:50
@Jake3231 why are you even doing this, this kind of override is pointless – Knight0fDragon Jul 01 '17 at 22:43

score 1 · Answer 2 · answered Jun 30 '17 at 14:36

1

Try this

override var texture: SKTexture? {
    get {
        return SKTexture()
    }
    set {

    }
}

obviously returning something a bit more useful.

answered Jun 30 '17 at 14:36

iCyberPaul

650
4
15

Thanks! My plan is to use `SKTexture.init(imageNamed: "someImage")` to give the class a specific texture. How would I do that with the code you provided? – Jake3231 Jun 30 '17 at 14:47
Have you tried replacing SKTexture with the init you have above. It should work. – iCyberPaul Jun 30 '17 at 14:51

score 1 · Answer 3 · answered Jun 30 '17 at 19:03

1

In your subclass you need to do this.

override var texture:SKTexture? {
    get { 
        return super.texture
    }
    set {
        super.texture = newValue
    }
}

answered Jun 30 '17 at 19:03

Kwaku Eshun

151
2
7

score 0 · Answer 4 · answered Jun 30 '17 at 18:27

From all my reading, I do not think overriding is the approach you want, you want to create a convenience init

class classTwo: classOne {
    convenience init()
    {
        let texture = SKTexture(imageNamed:"myImage")
        self.init(texture,.white,texure.size)
    }    

    required init?(coder aDecoder: NSCoder) {
        super.init(coder:aDecoder)
    }
}

Then to use it, you just need to do classTwo()

(Note, this has not been tested, so I may have typos, the general concept is here though)

Swift Unable to Override Variables in Subclass

4 Answers4