将 JSON 转换为 Swift 时出现问题“无法读取数据，因为它的格式不正确。”

Question

当我从 coinapi.com (https://rest-sandbox.coinapi.io/v1/assets/?apikey=72869C8A-D49B-4DC5-9A3B-17D9804AEE97) 转换 JSON 时，我遇到了一个问题“无法读取数据，因为它的格式不正确”。

转换后的结果是：

struct CryptListStruct: Codable {

    let assetID, name: String
    let typeIsCrypto: Int
    let dataQuoteStart, dataQuoteEnd, dataOrderbookStart, dataOrderbookEnd: String
    let dataTradeStart, dataTradeEnd: String
    let dataSymbolsCount: Int
    let volume1HrsUsd, volume1DayUsd: Double
    let volume1MthUsd: Int
    let priceUsd: Double?
    let idIcon, dataStart, dataEnd: String

    enum CodingKeys: String, CodingKey {
        case assetID = "asset_id"
        case name
        case typeIsCrypto = "type_is_crypto"
        case dataQuoteStart = "data_quote_start"
        case dataQuoteEnd = "data_quote_end"
        case dataOrderbookStart = "data_orderbook_start"
        case dataOrderbookEnd = "data_orderbook_end"
        case dataTradeStart = "data_trade_start"
        case dataTradeEnd = "data_trade_end"
        case dataSymbolsCount = "data_symbols_count"
        case volume1HrsUsd = "volume_1hrs_usd"
        case volume1DayUsd = "volume_1day_usd"
        case volume1MthUsd = "volume_1mth_usd"
        case priceUsd = "price_usd"
        case idIcon = "id_icon"
        case dataStart = "data_start"
        case dataEnd = "data_end"
    }
}

我认为这是因为那里有很多数据，而且它们不一样。如何获得正确的模型？

这就是我的函数的样子：

    
    
    func getCryptList(_ completion: @escaping (CryptListStruct) -> Void, _ error: @escaping (String) -> Void){
    let header: [String: String] = [:]
       self.get(url: "https://rest.coinapi.io/v1/assets/?apikey=367FB27A-371B-4DBD-AB81-E98AAFE857B2", header: header, completion: {
            (data) in
            do {
                guard let data = data else {return}
                let crpytList = try JSONDecoder().decode(CryptListStruct.self, from: data)
                DispatchQueue.main.async {
                    completion(crpytList)
                }
            } catch let err {
                       error(err.localizedDescription)
                   }
               }, error: error)
    }
``

Answer 1

首先

从不print(error.localizedDescription)。

在 JSONDecoder 捕获块中。您会收到一条通用但毫无意义的错误消息。

总是打印整个错误，DecodingErrors 非常具有描述性

print(error)

---

您的代码包含三个主要错误，其中一个（错误 #3）多次出现

错误 #1

typeMismatch(Swift.Dictionary, Swift.DecodingError.Context(codingPath: [], debugDescription: "应解码 Dictionary 但找到了一个数组。强>”，基础错误：无））

表示根对象为数组，JSON明确以[开头

解决方案：解码[CryptListStruct].self

---

错误 #2

dataCorrupted(Swift.DecodingError.Context(codingPath: [_JSONKey(stringValue: "Index 0", intValue: 0), CodingKeys(stringValue: "volume_1mth_usd", intValue: nil)], debugDescription: "解析的 JSON 编号 不适合 Int。”，underlyingError: nil))

表示接收到的值3699822674922524.74实际上是一个Double。

解决方案：声明

let volume1MthUsd: Double

---

错误 #3

keyNotFound(CodingKeys(stringValue: "id_icon", intValue: nil), Swift.DecodingError.Context(codingPath: [_JSONKey(stringValue: "Index 4", intValue: 4)], debugDescription: "没有值关联键 CodingKeys(stringValue: "id_icon", intValue: nil) ("id_icon").", underlyingError: nil))

表示在数组的第 5 项中（至少）缺少键 id_icon。

解决方案：将类型声明为可选

let idIcon : String?

dataTradeStart、dataTradeEnd、dataQuoteStart、dataQuoteEnd、dataOrderbookStart、dataOrderbookEnd、dataStart、dataEnd 出现同样的错误

let dataQuoteStart, dataQuoteEnd, dataOrderbookStart, dataOrderbookEnd: String?
let dataTradeStart, dataTradeEnd : String?
let dataStart, dataEnd: String?

---

旁注：

如果将assetID 替换为assetId 并添加convertFromSnakeCase 密钥解码策略，则可以删除整个 CodingKeys 枚举

let decoder = JSONDecoder()
decoder.keyDecodingStrategy = .convertFromSnakeCase
let crpytList = try decoder.decode([CryptListStruct].self, from: data)

Answer 2

响应模型

typealias CryptResult = [CryptListElement]

// MARK: - CryptListElement
struct CryptListElement: Codable {
    let assetID, name: String
    let typeIsCrypto: Int
    let dataQuoteStart, dataQuoteEnd, dataOrderbookStart, dataOrderbookEnd: String?
    let dataTradeStart, dataTradeEnd: String?
    let dataSymbolsCount: Int
    let volume1HrsUsd, volume1DayUsd, volume1MthUsd: Double
    let priceUsd: Double?
    let idIcon, dataStart, dataEnd: String?

    enum CodingKeys: String, CodingKey {
        case assetID = "asset_id"
        case name
        case typeIsCrypto = "type_is_crypto"
        case dataQuoteStart = "data_quote_start"
        case dataQuoteEnd = "data_quote_end"
        case dataOrderbookStart = "data_orderbook_start"
        case dataOrderbookEnd = "data_orderbook_end"
        case dataTradeStart = "data_trade_start"
        case dataTradeEnd = "data_trade_end"
        case dataSymbolsCount = "data_symbols_count"
        case volume1HrsUsd = "volume_1hrs_usd"
        case volume1DayUsd = "volume_1day_usd"
        case volume1MthUsd = "volume_1mth_usd"
        case priceUsd = "price_usd"
        case idIcon = "id_icon"
        case dataStart = "data_start"
        case dataEnd = "data_end"
    }
}

解码器代码：

 let result = try? newJSONDecoder().decode(CryptResult.self, from: jsonData)

我们需要使用 CryptResult 而不是 CryptListElement

Answer 3

试试这个（注意选项和volume1MthUsd：Double），对我有用：

struct CryptListStruct: Codable {

    let assetID, name: String
    let typeIsCrypto: Int
    let dataQuoteStart, dataQuoteEnd, dataOrderbookStart, dataOrderbookEnd: String?
    let dataTradeStart, dataTradeEnd: String?
    let dataSymbolsCount: Int
    let volume1HrsUsd, volume1DayUsd, volume1MthUsd: Double
    let priceUsd: Double?
    let idIcon, dataStart, dataEnd: String?

    enum CodingKeys: String, CodingKey {
        case assetID = "asset_id"
        case name
        case typeIsCrypto = "type_is_crypto"
        case dataQuoteStart = "data_quote_start"
        case dataQuoteEnd = "data_quote_end"
        case dataOrderbookStart = "data_orderbook_start"
        case dataOrderbookEnd = "data_orderbook_end"
        case dataTradeStart = "data_trade_start"
        case dataTradeEnd = "data_trade_end"
        case dataSymbolsCount = "data_symbols_count"
        case volume1HrsUsd = "volume_1hrs_usd"
        case volume1DayUsd = "volume_1day_usd"
        case volume1MthUsd = "volume_1mth_usd"
        case priceUsd = "price_usd"
        case idIcon = "id_icon"
        case dataStart = "data_start"
        case dataEnd = "data_end"
    }
}

编辑1：

这就是我测试答案的方式：

import SwiftUI

@main
struct TestApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}
    struct ContentView: View {
    @State var cryptList = [CryptListStruct]()
    
    var body: some View {
        Text(cryptList.count > 0 ? "fetched \(cryptList.count)" : "fetching...")
            .task {
                cryptList = await fetchThem()
                print("\n----> cryptList: \(cryptList.count) \n")
            }
        // using closure
        //.onAppear {
        //    getCryptList() { list in
        //        cryptList = list
        //    }
        // }
    }
    
    private func fetchThem<T: Decodable>() async -> [T] {
        var url = URL(string: "https://rest-sandbox.coinapi.io/v1/assets/?apikey=72869C8A-D49B-4DC5-9A3B-17D9804AEE97")!
        do {
            let (data, response) = try await URLSession.shared.data(for: URLRequest(url: url))
            guard let httpResponse = response as? HTTPURLResponse, httpResponse.statusCode == 200 else {
                print(URLError(.badServerResponse))
                return []
            }
            return try JSONDecoder().decode([T].self, from: data)
        }
        catch {
            return []
        }
    }
}

EDIT2：使用闭包样式：

private func getCryptList(_ completion: @escaping ([CryptListStruct]) -> Void) {
    URLSession.shared.dataTask(with: URL(string: "https://rest-sandbox.coinapi.io/v1/assets/?apikey=72869C8A-D49B-4DC5-9A3B-17D9804AEE97")!,
                               completionHandler: { data, response, error in
        guard let data = data, error == nil else {
            print("error: \(error?.localizedDescription as Optional)")
            return
        }
        do {
            let cryptList = try JSONDecoder().decode([CryptListStruct].self, from: data)
            completion(cryptList)
        }
        catch {
            print(String(describing: error))
        }
    }).resume()
}