Swift：Enum’无法构造,因为它没有可访问的初始值设定项’

‘BlockColor’ cannot be constructed because it has no accessible
initializers

import Foundation
import SpriteKit

let NumberOfColors: UInt32 = 6

enum BlockColor: Int,Printable {

case Blue = 0,Orange,Purple,Red,Teal,Yellow

var spriteName: String {
    switch self {
    case .Blue:
        return "blue"
    case .Orange:
        return "orange"
    case .Purple:
        return "purple"
    case .Red:
        return "red"
    case .Teal:
        return "teal"
    case .Yellow:
        return "yellow"
        }
}

var description: String {
    return self.spriteName
}

static func random() -> BlockColor {
    return BlockColor(rawValue:Int(arc4random_uniform(NumberOfColors)))!
}
}

我在这一行得到了一个错误

return BlockColor(rawValue:Int(arc4random_uniform(NumberOfColors)))!

我已多次查看我的代码,但我找不到错误的位置