我已经为我的项目中的一些类实现了自定义JSON解码.我已经设置了常用的CodingKeys枚举，并实现了自定义的编码和解码函数.一切正常.

但是我还为解码过程实现了一些方便的函数，这些函数可以捕获JSONDecoder的KeyedDecodingContainer抛出的任何错误，并返回一些正常的结果.因为这些函数不需要在类之间变化，所以我想将它们移出类，但大多数示例将编码键定义为类中的硬编码枚举.

下面是要解码的类:

class User : Equatable, Codable
{
    var ID: String = ""
    var pw: String = ""
    var username:  String = ""
    var firstName: String = ""
    var lastName: String = ""
    var EMail: String = ""
    var phoneNbr: String = ""
    var avatarURL: String = ""
    var mediaServiceID: String = ""
    var validated: Bool = false // E-mail is confirmed.

    // Equatable
    static func == (lhs: User, rhs: User) -> Bool
    {
        return lhs.ID == rhs.ID
    }

    // Codable
    enum CodingKeys: String, CodingKey
    {
        case ID = "ID"
        case pw = "pw"
        case username = "username"
        case firstName = "firstName"
        case lastName = "lastName"
        case EMail = "EMail"
        case phoneNbr = "phoneNbr"
        case avatarURL = "avatarURL"
        case mediaServiceID = "mediaServiceID"
        case validated = "validated"
    }

    required init(from decoder: Decoder) throws
    {
        var container: KeyedDecodingContainer<CodingKeys>
        do
        {
            container = try decoder.container(keyedBy: CodingKeys.self)
        }
        
        ID =                safeStringDecode(container: container, forKey: .ID)
        pw =                safeStringDecode(container: container, forKey: .pw)
        username =          safeStringDecode(container: container, forKey: .username)
        firstName =         safeStringDecode(container: container, forKey: .firstName)
        lastName =          safeStringDecode(container: container, forKey: .lastName)
        EMail =             safeStringDecode(container: container, forKey: .EMail)
        phoneNbr =          safeStringDecode(container: container, forKey: .phoneNbr)
        avatarURL =         safeStringDecode(container: container, forKey: .avatarURL)
        mediaServiceID =    safeStringDecode(container: container, forKey: .mediaServiceID)
        validated =         safeBoolDecode(container: container, forKey: .validated)
    }

    func safeStringDecode(container: KeyedDecodingContainer<CodingKeys>, forKey: CodingKeys) -> String
    {
        var result: String
        do
        {
            result = try container.decode(String.self, forKey: forKey)
        }
        catch
        {
            result = ""
        }
        
        return result
    }
    
    func safeBoolDecode(container: KeyedDecodingContainer<CodingKeys>, forKey: CodingKeys) -> Bool
    {
        // First try int, because that's what MySQL/MariaDB return for bools.
        var result: Int
        do
        {
            result = try container.decode(Int.self, forKey: forKey)
            return result == 1
        }
        catch
        {
            // Let's see if it's a 'true'/'false' string.
            var stringResult: String
            do
            {
                stringResult = try container.decode(String.self, forKey: forKey)
                return stringResult == "true"
            }
            catch
            {
                return false
            }
        }
    }

I want to move those safeDecode methods out of this class and into a general utility namespace. But that means I can't hard-code the coding keys as an enum in the class, so I need to pass them in as an array or dictionary. It seems like it should be simple, but thus far I haven't seen a succinct solution. #3 in this post seems close, but I don't really understand some of the logic: How do I use custom keys with Swift 4's Decodable protocol?

"safeDecode"函数的基本原理是，如果任何值丢失或为nil，解码对象将完全失败，这是完全可能的，因为这些列在我的数据库中是可为nullable的.为了防止没有方便的功能，我想我必须在一个单独的do/catch对中 for each 成员进行解码try .非常乏味但我并不知道你在try ？语法来逐行捕获此内容.因此，现在我只需要布尔帮助器来处理不同数据库的布尔类型.我把它放在一个KeyedDecodingContainer扩展中，就像@Alexander善意建议的那样.