如何在 Swift 中访问其他类中的枚举值？

Question

我正在尝试使用场景工具包快速设置粒子发射器的属性。 我觉得很愚蠢，因为我不知道如何设置设置为枚举的常量。 代码如下：

//Create emitter
let emitter = SCNParticleSystem()

//set up the emitter trying to use the enum values
emitter.birthLocation = SCNParticleBirthLocation.SCNParticleBirthLocationSurface

//I have tried a few other ways including:
emitter.birthLocation = .SCNParticleBirthLocationSurface
emitter.birthLocation = SCNParticleSystem.SCNParticleBirthLocation.SCNParticleBirthLocationSurface

这不是我在不同类中使用枚举时遇到的唯一问题，所以我认为我有一些根本性的错误。 苹果框架参考链接，以防万一：https://developer.apple.com/library/prerelease/ios/documentation/SceneKit/Reference/SCNParticleSystem_Class/index.html#//apple_ref/occ/cl/SCNParticleSystem

最后是我的整个代码，以防万一我做错了完全不同的事情

import Foundation
import SceneKit

class NextLevelScene: SCNScene{

override init(){
    super.init()
    let nextLevel: SCNNode = SCNNode()
    let text: SCNGeometry = SCNText(string: "Next Level", extrusionDepth: 0.0)
    let material = UIColor.blueColor()
    text.firstMaterial!.diffuse.contents = material
    nextLevel.geometry = text

    let exp = SCNParticleSystem()
    exp.loops = true
    exp.birthRate = 5000
    exp.emissionDuration = 0.2
    exp.spreadingAngle = 180
    exp.particleDiesOnCollision = true
    exp.particleLifeSpan = 0.2
    exp.particleLifeSpanVariation = 0.05
    exp.particleVelocity = 20
    exp.particleVelocityVariation = 3
    exp.particleSize = 0.05
    exp.stretchFactor = 0.02
    exp.particleColor = UIColor.redColor()
    exp.emitterShape = text
    //Error here
    exp.birthLocation = SCNParticleBirthLocation.SCNParticleBirthLocationSurface
    self.addParticleSystem(exp, withTransform: SCNMatrix4MakeRotation(0, 0, 0, 0))


    self.rootNode.addChildNode(nextLevel)
}

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

提前致谢！

Answer 1

如果您在 Xcode 源文件中按住 Command 键单击 birthLocation 以获取 定义属性，然后按住 Command 键单击 SCNParticleBirthLocation 然后你会看到它在 Swift 中被声明为

enum SCNParticleBirthLocation : Int {

    case Surface //particles are emitted on the surface of the emitter shape.
    case Volume //particles are emitted inside the volume of the emitter shape.
    case Vertex //particles are emitted on the vertices of the emitter shape.
}

所以你只需要

emitter.birthLocation = SCNParticleBirthLocation.Surface

可以缩短（由于自动类型推断）

emitter.birthLocation = .Surface