json - 使用 Swift 4 Decodable 解析 JSON

Question

每次尝试在我的程序中解析 JSON 时，我都会遇到以下错误。我似乎无法弄清楚。

“预期解码 String 但发现了一个数组。”, underlyingError: nil

这是我一直在纠结的代码:

struct Book: Decodable {
    let id: Int
    let title: String
    let chapters: Int
    var pages: [Page]?
}

struct Page: Decodable {
    let id: Int
    let text: [String]
}

struct Chapter: Decodable {
    var chapterNumber: Int
}

func fetchJSON() {
    let urlString = "https://api.myjson.com/bins/kzqh3"
    guard let url = URL(string: urlString) else { return }

    URLSession.shared.dataTask(with: url) { (data, _, err) in
        if let err = err {
            print("Failed to fetch data from", err)
            return
        }
        guard let data = data else { return }
        do {
            let decoder = JSONDecoder()
            let books = try decoder.decode([Book].self, from: data)
            books.forEach({print($0.title)})
        } catch let jsonErr {
            print("Failed to parse json:", jsonErr)
        }
    }.resume()
}

Answer 1

您确定这是真正的错误消息吗？

其实错误应该是

"Expected to decode String but found a dictionary instead."

key text 的值不是字符串数组，而是字典数组

struct Page: Decodable {
    let id: Int
    let text: [[String:String]]
}

不需要结构 Chapter。

---

或者编写一个自定义初始化程序，并将包含章节编号作为键和文本作为值的字典解码到 Chapter 的数组中

struct Book: Decodable {
   let id: Int
   let title: String
   let chapters: Int
   let pages: [Page]
}

struct Page: Decodable {
    let id: Int
    var chapters = [Chapter]()

    private enum CodingKeys : String, CodingKey { case id, chapters = "text" }

    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        id = try container.decode(Int.self, forKey: .id)
        var arrayContainer = try container.nestedUnkeyedContainer(forKey: .chapters)
        while !arrayContainer.isAtEnd {
            let chapterDict = try arrayContainer.decode([String:String].self)
            for (key, value) in chapterDict {
                chapters.append(Chapter(number: Int(key)!, text: value))
            }
        }
    }
}

struct Chapter: Decodable {
    let number : Int
    let text : String
}