可编码的自定义类类型属性不能从 JSON 初始化自己的属性

Question

My Json：

{  
"message":"OK",
"response":[  
{  
"article_id":"201802062200722818",
"lead":"Poliisi vapautti naisen ja otti miehen kiinni. Satakunnan käräjäoikeus vangitsi miehen tiistaina.",
"headline":"Poliisi epäilee: 19-vuotias raumalaismies piti alaikäistä naista mökillä vankina",
"title":"Poliisi epäilee: 19-vuotias raumalaismies piti alaikäistä naista mökillä vankina",
"service_name":"iltalehti",
"main_image_name":"cae51c694cc7f31257290ff96489f3cf852329a887509621b29a27fbaa0f8894.jpg",
"category":{  
"category_name":"kotimaa",
"description":"Kotimaan uutiset",
"parent_category":{  
"category_name":"uutiset",
"description":"Uutiset",
"parent_category":null
}
},
"main_image_urls":{  
"default":"https://img.ilcdn.fi/PcWFp0weItXN2WAWKBXCO_H2VsQ=/510x/img-s3.ilcdn.fi/cae51c694cc7f31257290ff96489f3cf852329a887509621b29a27fbaa0f8894.jpg",
"size30":"https://img.ilcdn.fi/_LNHr84u93ntg3tX37oHyGBlRNA=/30x/img-s3.ilcdn.fi/cae51c694cc7f31257290ff96489f3cf852329a887509621b29a27fbaa0f8894.jpg",
"size98":"https://img.ilcdn.fi/r624bQFqaJ3xqrMScif38JH6SBM=/98x/img-s3.ilcdn.fi/cae51c694cc7f31257290ff96489f3cf852329a887509621b29a27fbaa0f8894.jpg",
"size138":"https://img.ilcdn.fi/dyemZCdMpjAFTnnD5JiYLh3WGJI=/138x/img-s3.ilcdn.fi/cae51c694cc7f31257290ff96489f3cf852329a887509621b29a27fbaa0f8894.jpg",
"size244":"https://img.ilcdn.fi/2AiJpLa4oLxEDE0jL_LazhOiTMM=/244x/img-s3.ilcdn.fi/cae51c694cc7f31257290ff96489f3cf852329a887509621b29a27fbaa0f8894.jpg",
"size293":"https://img.ilcdn.fi/iyAZVQ0ufAHrX2inGCiE9QPQjMU=/293x/img-s3.ilcdn.fi/cae51c694cc7f31257290ff96489f3cf852329a887509621b29a27fbaa0f8894.jpg",
"size310":"https://img.ilcdn.fi/XGmL7EEqo0OR5Vzvbel1hSeTmHI=/310x/img-s3.ilcdn.fi/cae51c694cc7f31257290ff96489f3cf852329a887509621b29a27fbaa0f8894.jpg",
"size510":"https://img.ilcdn.fi/PcWFp0weItXN2WAWKBXCO_H2VsQ=/510x/img-s3.ilcdn.fi/cae51c694cc7f31257290ff96489f3cf852329a887509621b29a27fbaa0f8894.jpg",
"size820":"https://img.ilcdn.fi/N-XV5ZqQASGpvUe-3DAcq4i1928=/820x/img-s3.ilcdn.fi/cae51c694cc7f31257290ff96489f3cf852329a887509621b29a27fbaa0f8894.jpg",
"size1024":"https://img.ilcdn.fi/J5Cm5P2SJMNymHza7s3LdEEvKLg=/1024x/img-s3.ilcdn.fi/cae51c694cc7f31257290ff96489f3cf852329a887509621b29a27fbaa0f8894.jpg"
},
"published_at":"2018-02-06T10:42:40+02:00",
"updated_at":null
}
]
}

我的Codable模型类

文章.swift

import Foundation
struct Articles : Codable {
let message : String?
let response : [Article]?
enum CodingKeys: String, CodingKey {
case message = "message"
case response = "response"
}
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
message = try values.decodeIfPresent(String.self, forKey: .message)
response = try values.decodeIfPresent([Article].self, forKey: .response)
}
}

文章.swift

import Foundation
struct Article : Codable {
let article_id : String?
let lead : String?
let headline : String?
let title : String?
let service_name : String?
let main_image_name : String?
let category : Category?
let main_image_urls : Main_image_urls?
let published_at : String?
let updated_at : String?
enum CodingKeys: String, CodingKey {
case article_id = "article_id"
case lead = "lead"
case headline = "headline"
case title = "title"
case service_name = "service_name"
case main_image_name = "main_image_name"
case category
case main_image_urls
case published_at = "published_at"
case updated_at = "updated_at"
}
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
article_id = try values.decodeIfPresent(String.self, forKey: .article_id)
lead = try values.decodeIfPresent(String.self, forKey: .lead)
headline = try values.decodeIfPresent(String.self, forKey: .headline)
title = try values.decodeIfPresent(String.self, forKey: .title)
service_name = try values.decodeIfPresent(String.self, forKey: .service_name)
main_image_name = try values.decodeIfPresent(String.self, forKey: .main_image_name)
category = try Category(from: decoder)
main_image_urls = try Main_image_urls(from: decoder)
published_at = try values.decodeIfPresent(String.self, forKey: .published_at)
updated_at = try values.decodeIfPresent(String.self, forKey: .updated_at)
}
}

类别.swift

import Foundation
struct Category : Codable {
let category_name : String?
let description : String?
let parent_category : Parent_category?
enum CodingKeys: String, CodingKey {
case category_name = "category_name"
case description = "description"
case parent_category
}
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
category_name = try values.decodeIfPresent(String.self, forKey: .category_name)
description = try values.decodeIfPresent(String.self, forKey: .description)
parent_category = try Parent_category(from: decoder)
}
}

Parent_category.swift

import Foundation
struct Parent_category : Codable {
let category_name : String?
let description : String?
let parent_category : String?
enum CodingKeys: String, CodingKey {
case category_name = "category_name"
case description = "description"
case parent_category = "parent_category"
}
init(from decoder: Decoder) throws {
let values = try decoder.container(keyedBy: CodingKeys.self)
category_name = try values.decodeIfPresent(String.self, forKey: .category_name)
description = try values.decodeIfPresent(String.self, forKey: .description)
parent_category = try values.decodeIfPresent(String.self, forKey: .parent_category)
}
}

问题：

我正在尝试使用Codable协议从 JSON 初始化我的模型类。它适用于本机数据类型(字符串、Int 等)，但如果结构包含自定义类型属性对象，则不会初始化该自定义结构(类)的属性。

示例：Category是结构Article中的自定义类型对象。每个自定义类都负责初始化其属性，确认Codable协议并具有自己的init(from decoder: Decoder)方法。

但不知何故，category和其他自定义类型无法初始化自己的属性。(例如category_name = nilCategory类中，Parent_category和Main_image_urls也发生了同样的情况)，我得到以下结果：(某些值为零)

控制台登录 xcode

po article
▿ Optional<Article>
▿ some : Article
▿ article_id : Optional<String>
- some : "201802062200722818"
▿ lead : Optional<String>
- some : "Poliisi vapautti naisen ja otti miehen kiinni. Satakunnan käräjäoikeus vangitsi miehen tiistaina."
▿ headline : Optional<String>
- some : "Poliisi epäilee: 19-vuotias raumalaismies piti alaikäistä naista mökillä vankina"
▿ title : Optional<String>
- some : "Poliisi epäilee: 19-vuotias raumalaismies piti alaikäistä naista mökillä vankina"
▿ service_name : Optional<String>
- some : "iltalehti"
▿ main_image_name : Optional<String>
- some : "cae51c694cc7f31257290ff96489f3cf852329a887509621b29a27fbaa0f8894.jpg"
▿ category : Optional<Category>
▿ some : Category
- category_name : nil
- description : nil
▿ parent_category : Optional<Parent_category>
▿ some : Parent_category
- category_name : nil
- description : nil
- parent_category : nil
▿ main_image_urls : Optional<Main_image_urls>
▿ some : Main_image_urls
- default : nil
- size30 : nil
- size98 : nil
- size138 : nil
- size244 : nil
- size293 : nil
- size310 : nil
- size510 : nil
- size820 : nil
- size1024 : nil
▿ published_at : Optional<String>
- some : "2018-02-06T10:42:40+02:00"
- updated_at : nil

我错过了什么吗？ 请帮助大家：-)

Answer 1

在Article.swift尝试更改以下行

category = try Category(from: decoder)
main_image_urls = try Main_image_urls(from: decoder)

自

category = values.decodeIfPresent(Category.self, forKey: .category)
main_image_urls = values.decodeIfPresent(Main_image_urls.self, forKey: .main_image_urls)

您的类Main_image_urls也应符合可编纂的内容。

您也可以尝试省略init(from decoder: Decoder)方法，让编译器合成它。这在具有自定义编码键枚举时也有效。

更新：

同时更改Category.swift中的以下行

parent_category = try Parent_category(from: decoder)

自

parent_category = values.decodeIfPresent(Parent_category.self, forKey: .parentCategory)