SpriteKit 无法从 sks 文件中解压 SKEmitterNode 子类

Question

我有以下代码：

final class PassthroughEmitterNode: SKEmitterNode {
  
  static func load(fnWithoutExtension: String, in bundle: Bundle) -> SKEmitterNode? {
    guard
      let sksPath = bundle.path(forResource: fnWithoutExtension, ofType: "sks"),
      let sksData = try? Data(contentsOf: URL(fileURLWithPath: sksPath)),
      let unarchiver = try? NSKeyedUnarchiver(forReadingFrom: sksData),
      let texturePath = bundle.path(forResource: fnWithoutExtension, ofType: "png"),
      let textureImage = UIImage(contentsOfFile: texturePath)
    else { return nil }
    
    // Required to decode into subclass
    unarchiver.setClass(self.classForKeyedUnarchiver(), forClassName: "SKEmitterNode")
    let emitter = unarchiver.decodeObject(forKey: NSKeyedArchiveRootObjectKey) as? PassthroughEmitterNode
    unarchiver.finishDecoding()
    
    guard let emitter else { return nil }
    
    // We still need to set texture, because the texture file is not in main bundle
    emitter.particleTexture = SKTexture(image: textureImage)
    
    // Have to enable user interaction to receive touch
    emitter.isUserInteractionEnabled = true
    
    return emitter
  }
}

这与从 SKS 文件读取 SKScene 子类实例非常相似（例如：将 sks 文件与 SKScene 子类一起使用）。

但是，这行不通。解档器的解码始终返回 nil。

但是解档到

SKEmitterNode

类本身是有效的。子类不起作用。

Answer 1

我想我知道为什么这不起作用。

当您从

GameScene

文件解码自定义场景（例如

SKScene

的

sks

子类）时，您可以将自定义类的名称放入

sks

文件中。

不幸的是，似乎不可能对 SKEmitterNode 做同样的事情。事实上，如果您打开代表发射器的

sks

文件并将检查器转到右侧，则

Custom class inspector

面板不存在。

因此似乎不可能将包含发射器的 sks 文件解码为

SKEmitterNode

的子类。

另一种方法

但是，我们可以尝试其他方法：

1. 解码

   SKEmitterNode

2. 从

   PassthroughEmitterNode

    创建 

   SKEmitterNode

为了做到这一点，让我们添加这个 init

public final class PassthroughEmitterNode: SKEmitterNode {
    
    init(emitterNode: SKEmitterNode) {
        super.init()

        self.emissionAngle = emitterNode.emissionAngle
        self.emissionAngleRange = emitterNode.emissionAngleRange
        self.numParticlesToEmit = emitterNode.numParticlesToEmit
        self.particleAlpha = emitterNode.particleAlpha
        self.particleAlphaRange = emitterNode.particleAlphaRange
        self.particleAlphaSpeed = emitterNode.particleAlphaSpeed
        self.particleBirthRate = emitterNode.particleBirthRate
        self.particleBlendMode = emitterNode.particleBlendMode
        self.particleColor = emitterNode.particleColor
        self.particleColorBlendFactor = emitterNode.particleColorBlendFactor
        self.particleColorBlendFactorRange = emitterNode.particleColorBlendFactorRange
        self.particleColorBlendFactorSpeed = emitterNode.particleColorBlendFactorSpeed
        self.particleLifetime = emitterNode.particleLifetime
        self.particleLifetimeRange = emitterNode.particleLifetimeRange
        self.particlePositionRange = emitterNode.particlePositionRange
        self.particleRotation = emitterNode.particleRotation
        self.particleRotationRange = emitterNode.particleRotationRange
        self.particleRotationSpeed = emitterNode.particleRotationSpeed
        self.particleScale = emitterNode.particleScale
        self.particleScaleRange = emitterNode.particleScaleRange
        self.particleScaleSpeed = emitterNode.particleScaleSpeed
        self.particleSpeed = emitterNode.particleSpeed
        self.particleSpeedRange = emitterNode.particleSpeedRange
        self.particleTexture = emitterNode.particleTexture
        self.position = emitterNode.position
        self.xAcceleration = emitterNode.xAcceleration
        self.yAcceleration = emitterNode.yAcceleration
        // TODO: Add additional properties I might have forgot.
    }
    
    @available(*, unavailable)
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

就是这样。

现在您可以解码标准

SKEmitterNode

并将其转换为您的

PassthroughEmitterNode

let emitterNode: SKEmitterNode = ... // Decode as usual
let passthroughEmitterNode = PassthroughEmitterNode(emitterNode: emitterNode)

如果

PassthroughEmitterNode

与

SKEmitterNode

相比具有额外的属性怎么办？

这些附加属性的值不能来自 sks 文件，因为它们没有位置。因此，您需要使用一些默认值或自定义逻辑来填充它们。