Testing GameplayKit's GKSKNodeComponent with SpriteKit.

GKSK.swift

/**
 
 # Testing GKSKNodeComponent
 
 Apple documentation: https://developer.apple.com/documentation/gameplaykit/gksknodecomponent
 
 A GKSKNodeComponent is a special class of component that contains a node by default.
 When a GKSKNodeComponent is added to an entity, the `node.entity` property of the node is automatically assigned.
 Whereas if we use a regular GKComponent with a node inside it, we must assign that property manually inside `didAddToEntity` and `willRemoveFromEntity`.
 Note that in both cases, the SpriteKit scene must hold a strong reference to the entity in order to retrieve it.
 
 
 Achraf Kassioui
 Created 28 October 2024
 updated 29 October 2024
 
 */

import SwiftUI
import SpriteKit
import GameplayKit

// MARK: SwiftUI

struct GKSKView: View {
    var body: some View {
         SpriteView(scene: GKSKScene())
            .ignoresSafeArea()
    }
}

#Preview {
    GKSKView()
}

class GKSKScene: SKScene {
    
    // MARK: Scene Setup
    
    /// An entity must be stored as a class property, not inside a closure, so that SpriteKit maintains a strong reference to it
    let myEntity = GKEntity()
    
    override func didMove(to view: SKView) {
        size = view.bounds.size
        anchorPoint = CGPoint(x: 0.5, y: 0.5)
        backgroundColor = .gray
        view.isMultipleTouchEnabled = true
        
        createEntities()
        
        /// An entity created inside this closure won't be retrievable outside the closure
        let entity = GKEntity()
        entity.addComponent(GKSKRenderingComponent(color: .systemRed, size: CGSize(width: 100, height: 100)))
        if let component = entity.component(ofType: GKSKRenderingComponent.self) {
            component.node.position.y = 100
            addChild(component.node)
            if let entity = component.node.entity {
                /// This works here, but not outside `didMove`
                print("Entity inside a closure: \(entity)")
            }
        }
    }
    
    func createEntities() {
        let component = GKSKRenderingComponent(color: .systemYellow, size: CGSize(width: 100, height: 100))
        /// We use the entity initialized with the class
        myEntity.addComponent(component)
        if let renderingComponent = myEntity.component(ofType: GKSKRenderingComponent.self) {
            addChild(renderingComponent.node)
        }
        print("Entity created with a strong reference: \(myEntity)")
    }
    
    // MARK: Touch
    
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        for touch in touches {
            let touchedNode = atPoint(touch.location(in: self))
            /// Only the strongly referenced entity will be found here
            print(touchedNode.entity ?? "No entity found on this node")
        }
    }
}

// MARK: Rendering Components

class GKSKRenderingComponent: GKSKNodeComponent {
    
    init(texture: SKTexture? = nil, color: SKColor, size: CGSize) {
        let sprite = SKSpriteNode(texture: texture, color: color, size: size)
        /// The passed in node will automatically manage its entity property
        super.init(node: sprite)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}