在 UserDefaults 上使用 NSKeyedArchiver 时属性重置

Question

我有一个 SKSpriteNode 对象数组，我想将它们持久化到 UserDefaults。在下面的代码 (or see demo project on GitHub) 中，我使用 NSKeyedUnarchiver 将数组编码为数据，然后再将其设置为默认值。但是当我取消归档数据时，对象的engineSize 属性被重置为默认值 0。

Car.swift

import SpriteKit

class Car: SKSpriteNode {
    var engineSize: Int = 0

    init() {
        super.init(texture: nil, color: .blue, size: CGSize(width: 100, height: 100))
    }

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

GameScene.swift

import SpriteKit

class GameScene: SKScene {
    let defaults = UserDefaults.standard
    var carArray = [Car]()

    override func didMove(to view: SKView) {
        for _ in 1...3 {
            let car = Car()
            car.engineSize = 2000
            carArray.append(car)
        }

        // Save to defaults
        defaults.set(NSKeyedArchiver.archivedData(withRootObject: carArray), forKey: "carArrayKey")

        // Restore from defaults
        let arrayData = defaults.data(forKey: "carArrayKey")
        carArray = NSKeyedUnarchiver.unarchiveObject(with: arrayData!) as! [Car]
    }

    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        for c in carArray {
            print("Car's engine size is \(c.engineSize)")
        }
    }
}

This answer 引导我尝试在 Car 类上实现编码器/解码器方法：

Car.swift（更新）

import SpriteKit

class Car: SKSpriteNode {
    var engineSize: Int = 0

    init() {
        super.init(texture: nil, color: .blue, size: CGSize(width: 100, height: 100))
    }

    required convenience public init(coder decoder: NSCoder) {
        self.init()

        if let engineSize = decoder.decodeObject(forKey: "engineSize") as? Int {
            self.engineSize = engineSize
        }
    }

    func encodeWithCoder(coder : NSCoder) {
        coder.encode(self.engineSize, forKey: "engineSize")
    }
}

但是，这似乎不起作用。 GameScene 仍在将 engineSize 打印为 0。我执行编码器/解码器是否错误？当engineSize 属性从默认值恢复时，我可以做些什么来防止它们重置为 0？

更新

这是我更新后的 Car 课程，因为我正试图让它与 rmaddy 的建议一起使用：

import SpriteKit

class Car: SKSpriteNode {
    var engineSize: Int = 0

    init() {
        super.init(texture: nil, color: .blue, size: CGSize(width: 100, height: 100))
    }

    required init?(coder decoder: NSCoder) {
        super.init(coder: decoder)
        if let engineSize = decoder.decodeObject(forKey: "engineSize") as? Int {
            self.engineSize = engineSize
        }
    }

    func encodeWithCoder(coder : NSCoder) {
        super.encode(with: coder)
        coder.encode(self.engineSize, forKey: "engineSize")
    }
}

代码编译并运行，但engineSize 属性在保存为默认值时仍被重置为 0。

Answer 1

我设法让这个工作。以下是更新后的GameScene 和Car 代码文件，其中NSCoding 已正确实现。

Car.swift

import SpriteKit

class Car: SKSpriteNode {
    var engineSize: Int = 0
    
    init() {
        super.init(texture: nil, color: .blue, size: CGSize(width: 100, height: 100))
    }
    
    required init(coder aDecoder: NSCoder) {
        engineSize = aDecoder.decodeInteger(forKey: "engineSize")
        super.init(texture: nil, color: .blue, size: CGSize(width: 100, height: 100))
    }
    
    override func encode(with aCoder: NSCoder) {
        aCoder.encode(engineSize, forKey: "engineSize")
    }
}

GameScene.swift

import SpriteKit

class GameScene: SKScene {
    let defaults = UserDefaults.standard
    var carArray = [Car]()
    
    override func didMove(to view: SKView) {
        for _ in 1...3 {
            let car = Car()
            car.engineSize = 2000
            carArray.append(car)
        }
        
        defaults.set(NSKeyedArchiver.archivedData(withRootObject: carArray), forKey: "carArrayKey")
        
        let arrayData = defaults.data(forKey: "carArrayKey")
        carArray = NSKeyedUnarchiver.unarchiveObject(with: arrayData!) as! [Car]
    }
    
    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
        for c in carArray {
            print("Car's engine size is \(c.engineSize)")
        }
    }
}

更新

如果您如上所示实现init(coder aDecoder: NSCoder) 和encode(with aCoder: NSCoder)，您可能会注意到某些类型属性（如color、position 或size）在您归档/取消归档它们后会重置为其初始值.这是因为您现在提供了您自己的这两种方法的实现，因此您不能再依赖超类来为您处理类型属性的编码/解码。

您现在必须为您关心的所有属性实现编码/解码，包括您自己的自定义属性和类型的属性。例如：

required init(coder aDecoder: NSCoder) {
    super.init(texture: nil, color: .blue, size: CGSize(width: 100, height: 100))
    engineSize = aDecoder.decodeInteger(forKey: "engineSize")
    self.position = aDecoder.decodeCGPoint(forKey: "position")
    self.alpha = aDecoder.decodeObject(forKey: "alpha") as! CGFloat
    self.zPosition = aDecoder.decodeObject(forKey: "zPosition") as! CGFloat
    self.name = aDecoder.decodeObject(forKey: "name") as! String?
    self.colorBlendFactor = aDecoder.decodeObject(forKey: "colorBlendFactor") as! CGFloat
    self.color = aDecoder.decodeObject(forKey: "color") as! UIColor
    self.size = aDecoder.decodeCGSize(forKey: "size")
    self.texture = aDecoder.decodeObject(forKey: "texture") as! SKTexture?
}

override func encode(with aCoder: NSCoder) {
    aCoder.encode(engineSize, forKey: "engineSize")
    aCoder.encode(self.position, forKey: "position")
    aCoder.encode(self.alpha, forKey: "alpha")
    aCoder.encode(self.zPosition, forKey: "zPosition")
    aCoder.encode(self.name, forKey: "name")
    aCoder.encode(self.colorBlendFactor, forKey: "colorBlendFactor")
    aCoder.encode(self.color, forKey: "color")
    aCoder.encode(self.size, forKey: "size")
    aCoder.encode(self.texture, forKey: "texture")
}