与枚举类型的属性的可解码一致性

Posted 2023-02-18

【中文标题】与枚举类型的属性的可解码一致性

【英文标题】：Decodable conformance with property of enum type

【发布时间】：2018-07-24 19:35:26

【问题描述】：

我有这个枚举：

enum DealStatus:String 
    case PENDING = "Pending"
    case ACTIVE = "Active"
    case STOP = "Stop"
    case DECLINED = "Declined"
    case PAUSED = "Paused"

和结构：

struct ActiveDeals: Decodable 
    let keyword:            String
    let bookingType:        String
    let expiryDate:         Int
    let createdAt:          Int?
    let shopLocation:       String?
    let dealImages:         [DealImages]?
    let dealStatus:         String?
    let startingDate:       Int?

在结构中，我试图将枚举分配为dealStatus 的类型，如下所示：

struct ActiveDeals: Decodable 
        let keyword:            String
        let bookingType:        String
        let expiryDate:         Int
        let createdAt:          Int?
        let shopLocation:       String?
        let dealImages:         [DealImages]?
        let dealStatus:         DealStatus
        let startingDate:       Int?
    

但是我得到了一些编译器错误：

类型“ActiveDeals”不符合协议“Decodable”

协议需要类型为“Decodable”的初始化程序“init(from:)” (Swift.Decodable)

无法自动合成“可解码” 因为“DealStatus”不符合“Decodable”

【参考方案1】：

根据 Federico Zanetello 在他的帖子 Swift 4 Decodable: Beyond The Basics 中的说法，如果您需要解析原语子集（字符串、数字、布尔值等），Codable 和 Decobable 协议将可以正常工作。

在您的情况下，只需使 DealStatus 符合 Decodable （如建议 JeremyP) 应该可以解决您的问题。您可以检查 Playgrounds 创建自己的 JSON 数据并尝试解析它：

import UIKit

enum DealStatus: String, Decodable 
    case PENDING = "Pending"
    case ACTIVE = "Active"
    case STOP = "Stop"
    case DECLINED = "Declined"
    case PAUSED = "Paused"


struct ActiveDeals: Decodable 
    let keyword:            String
    let bookingType:        String
    let expiryDate:         Int
    let createdAt:          Int?
    let shopLocation:       String?
    let dealStatus:         DealStatus
    let startingDate:       Int?


let json = """

    "keyword": "Some keyword",
    "bookingType": "A type",
    "expiryDate": 123456,
    "createdAt": null,
    "shopLocation": null,
    "dealStatus": "Declined",
    "startingDate": 789456

""".data(using: .utf8)!

do 
    let deal = try JSONDecoder().decode(ActiveDeals.self, from: json)
    print(deal)
    print(deal.dealStatus)
 catch 
    print("error info: \(error)")

输出将是：

ActiveDeals(keyword: "Some keyword", bookingType: "A type", expiryDate: 123456, createdAt: nil, shopLocation: nil, dealStatus: __lldb_expr_61.DealStatus.DECLINED, startingDate: Optional(789456))
DECLINED

但是，要成为更好的程序员，您应该始终保持好奇心并尝试了解事物的原理，因此，如果您对如何遵守 Decodable 协议感兴趣（假设您需要自定义键、自定义错误或更复杂的数据结构），您可以这样做：

import UIKit

enum DealStatus: String 
    case PENDING = "Pending"
    case ACTIVE = "Active"
    case STOP = "Stop"
    case DECLINED = "Declined"
    case PAUSED = "Paused"


struct ActiveDeals 
    let keyword:            String
    let bookingType:        String
    let expiryDate:         Int
    let createdAt:          Int?
    let shopLocation:       String?
    let dealStatus:         DealStatus
    let startingDate:       Int?


extension ActiveDeals: Decodable 
    enum StructKeys: String, CodingKey 
        case keyword = "keyword"
        case bookingType = "booking_type"
        case expiryDate = "expiry_date"
        case createdAt = "created_at"
        case shopLocation = "shop_location"
        case dealStatus = "deal_status"
        case startingDate = "starting_date"
    

    enum DecodingError: Error 
        case dealStatus
    

    init(from decoder: Decoder) throws 
        let container = try decoder.container(keyedBy: StructKeys.self)

        let keyword = try container.decode(String.self, forKey: .keyword)
        let bookingType = try container.decode(String.self, forKey: .bookingType)
        let expiryDate = try container.decode(Int.self, forKey: .expiryDate)
        let createdAt = try container.decode(Int?.self, forKey: .createdAt)
        let shopLocation = try container.decode(String?.self, forKey: .shopLocation)

        //Get deal status as a raw string and then convert to your custom enum
        let dealStatusRaw = try container.decode(String.self, forKey: .dealStatus)
        guard let dealStatus = DealStatus(rawValue: dealStatusRaw) else 
            throw DecodingError.dealStatus
        

        let startingDate = try container.decode(Int?.self, forKey: .startingDate)

        self.init(keyword: keyword, bookingType: bookingType, expiryDate: expiryDate, createdAt: createdAt, shopLocation: shopLocation, dealStatus: dealStatus, startingDate: startingDate)
    


let json = """

    "keyword": "Some keyword",
    "booking_type": "A type",
    "expiry_date": 123456,
    "created_at": null,
    "shop_location": null,
    "deal_status": "Declined",
    "starting_date": 789456

""".data(using: .utf8)!

do 
    let deal = try JSONDecoder().decode(ActiveDeals.self, from: json)
    print(deal)
    print(deal.dealStatus)
 catch 
    print("error info: \(error)")

这种情况下输出还是一样的：

ActiveDeals(keyword: "Some keyword", bookingType: "A type", expiryDate: 123456, createdAt: nil, shopLocation: nil, dealStatus: __lldb_expr_67.DealStatus.DECLINED, startingDate: Optional(789456))
DECLINED

【讨论】：

感谢您的详细回答。对我帮助很大。

【参考方案2】：

错误表示类的某些属性不符合可解码协议。

将 Decodable 一致性添加到您的枚举中应该没问题。

extension DealStatus: Decodable  

【讨论】：

Codable => Decodable

是的，可解码。谢谢

@Sandeep 感谢您的回答。现在我在解析时遇到此错误： dataCorrupted(Swift.DecodingError.Context(codingPath: [O3.ActiveDealsContent.(CodingKeys in _300B97B81632ECD4F45F86E6B039153F).content, Foundation.(_JSONKey in _12768CA107A31EF2DCE034FD75B541C9)(stringValue: "Index 0," (0)), O3.ActiveDeals.(CodingKeys in _300B97B81632ECD4F45F86E6B039153F).dealStatus], debugDescription: "Cannot initialize DealStatus from invalid String value PENDING", underlyingError: nil))

【参考方案3】：

问题是 Swift 可以自动合成 Decodable 所需的方法，前提是结构的所有属性也是 Decodable 并且您的枚举不是 Decodable。

刚刚在操场上试了一下，看来你可以让你的枚举Decodable只需声明它是，Swift 会自动为你合成方法。即

enum DealStatus:String, Decodable  
//                      ^^^^^^^^^ This is all you need

    case PENDING = "Pending"
    case ACTIVE = "Active"
    case STOP = "Stop"
    case DECLINED = "Declined"
    case PAUSED = "Paused"

【讨论】：

感谢您的回答。现在我在解析时遇到此错误： dataCorrupted(Swift.DecodingError.Context(codingPath: [O3.ActiveDealsContent.(CodingKeys in _300B97B81632ECD4F45F86E6B039153F).content, Foundation.(_JSONKey in _12768CA107A31EF2DCE034FD75B541C9)(stringValue: "Index 0," (0)), O3.ActiveDeals.(CodingKeys in _300B97B81632ECD4F45F86E6B039153F).dealStatus], debugDescription: "Cannot initialize DealStatus from invalid String value PENDING", underlyingError: nil))

@SushilSharma 是的。您的数据包含字符串PENDING。 PENDING 案例的原始值是 Pending。将原始值设为大写。

但我需要原始值 CamelCased。因为我需要在我的一个标签中显示原始值。

@SushilSharma 然后将您的数据设为驼峰式大小写或为enum 创建自定义description，以“显示格式”返回值。或者实现init(from:)进行转换。