如何从 JSON 文件构建模型

Question

这是我第一次在 Swift 中使用 JSON，当我尝试使用我的模型解析文件时，出现以下错误：

给定的数据不是有效的 JSON。

我认为问题在于我如何制作模型。

我解析 JSON 的方式：

import SwiftUI

struct EmergencyView: View {
    let emergency: [EmergencyNumberModel]
    init() {
        let url = Bundle.main.url(forResource: "emergency",
                                  withExtension: "json")!
        let data = try! Data(contentsOf: url)
        emergency = try! JSONDecoder().decode([EmergencyNumberModel].self, from: data) //Error
    }
    
    var body: some View {
        List(emergency, id: \.id) { emer in
            
            if emer.Country != nil {
                Label(emer.Country, systemImage: "quote.bubble")
                    .font(.headline)
            } else{
                Text(emer.Country)
            }
        }
        navigationTitle("Emergency")
    }
}

这是我使用的 JSON 的一部分，“emergency.json”：

[
  {
    "Country": {
      "Name": "Afghanistan",
      "ISOCode": "AF",
      "ISONumeric": "4"
    },
    "Ambulance": {
      "All": [
        "112"
      ]
    },
    "Fire": {
      "All": [
        "119"
      ]
    },
    "Police": {
      "All": [
        "119"
      ]
    },
    "Dispatch": {
      "All": [
        null
      ]
    },
    "Member_112": false,
    "LocalOnly": true,
    "Notes": false
  },
 
 .
 .
 .

]

这是我的模型，“EmergencyNumberModel.swift”：

struct EmergencyNumberModel: Codable, Identifiable {
    var id = UUID()
    let Country: String
    let Ambulance: String
    let Fire: String
    let Police: String
    let Dispatch: String
}

我的模型中是否需要其他变量才能访问内部键或变量的数据类型错误？

Answer 1

使用https://app.quicktype.io/，生成快速结构， 这是使用 json 数据的一种基本方法：

struct EmergencyView: View {
    @State var emergencies: [EmergencyModel] = []  // <--- here
    
    var body: some View {
        List(emergencies) { emer in
            if emer.country.name.isEmpty {
                Text("no country name")
            } else {
                Label(emer.country.name, systemImage: "quote.bubble").font(.headline)
            }
        }
        .onAppear {
            if let emrgncy = loadData(from: "emergency") {  // <--- here
                emergencies = emrgncy
            }
        }
    }
    
    func loadData(from file: String) -> [EmergencyModel]? {
        do {
            if let filePath = Bundle.main.path(forResource: file, ofType: "json") {
                let data = try Data(contentsOf: URL(fileURLWithPath: filePath))
                let results = try JSONDecoder().decode([EmergencyModel].self, from: data)
                return results
            }
        } catch {
            print("----> error: \(error)") // <-- todo, deal with errors
        }
        return nil
    }
    
}

struct EmergencyModel: Identifiable, Codable {
    let id = UUID()  // <--- here
    let country: Country
    let ambulance, fire, police: Ambulance
    let dispatch: Dispatch
    let member112, localOnly, notes: Bool
    
    enum CodingKeys: String, CodingKey {
        case country = "Country"
        case ambulance = "Ambulance"
        case fire = "Fire"
        case police = "Police"
        case dispatch = "Dispatch"
        case member112 = "Member_112"
        case localOnly = "LocalOnly"
        case notes = "Notes"
    }
}

struct Ambulance: Codable {
    let all: [String]
    
    enum CodingKeys: String, CodingKey {
        case all = "All"
    }
}

struct Country: Codable {
    let name, isoCode, isoNumeric: String
    
    enum CodingKeys: String, CodingKey {
        case name = "Name"
        case isoCode = "ISOCode"
        case isoNumeric = "ISONumeric"
    }
}

struct Dispatch: Codable {
    let all: [JSONNull?]
    
    enum CodingKeys: String, CodingKey {
        case all = "All"
    }
}

class JSONNull: Codable, Hashable {
    
    public static func == (lhs: JSONNull, rhs: JSONNull) -> Bool {
        return true
    }
    
    func hash(into hasher: inout Hasher) {
       hasher.combine(0)
    }
    
    public init() {}
    
    public required init(from decoder: Decoder) throws {
        let container = try decoder.singleValueContainer()
        if !container.decodeNil() {
            throw DecodingError.typeMismatch(JSONNull.self, DecodingError.Context(codingPath: decoder.codingPath, debugDescription: "Wrong type for JSONNull"))
        }
    }
    
    public func encode(to encoder: Encoder) throws {
        var container = encoder.singleValueContainer()
        try container.encodeNil()
    }
}