将解码的 JSON 数据传递给 SwiftUI ContentView

Question

API 调用和 JSON 解码工作正常，因为我可以毫无问题地打印以控制 JSON 数据集中的任何项目。

这里是 API 调用和测试打印：

import Foundation
import SwiftUI
import Combine

class APICall : ObservableObject {

    @Published var summary: Summary?

        init () {
            pullSummary()
        }

    func pullSummary() {
        let urlCall = URL(string: "https://api.covid19api.com/summary")
        guard urlCall != nil else {
            print("Error reaching API")
            return
        }
        let session = URLSession.shared
        let dataTask = session.dataTask(with: urlCall!) { (data, response, error) in
            if error == nil && data != nil {
                let decoder = JSONDecoder()
                do {
                    let summary = try decoder.decode(Summary.self, from: data!)
                    print(summary.byCountry[40].cntry as Any)
                    DispatchQueue.main.async {
                        self.summary = summary
                    }
                }
                catch {
                    print("Server busy, try again in 5 min.")
                }
            }
        }
        dataTask.resume()
    }
}

这里是用于解码和数据对象结构的“摘要”数据模型的结构：

import Foundation

struct Summary: Decodable {
    let global: Global
    let byCountry: [ByCountry]
    let date: String

    enum CodingKeys: String, CodingKey {
        case global = "Global"
        case byCountry = "Countries"
        case date = "Date"
    }

    struct Global: Decodable {
        let globalNC: Int
        let globalTC: Int
        let globalND: Int
        let globalTD: Int
        let globalNR: Int
        let globalTR: Int

        enum CodingKeys: String, CodingKey {
            case globalNC = "NewConfirmed"
            case globalTC = "TotalConfirmed"
            case globalND = "NewDeaths"
            case globalTD = "TotalDeaths"
            case globalNR = "NewRecovered"
            case globalTR = "TotalRecovered"
        }
    }

    struct ByCountry: Decodable {
        let cntry: String?
        let ccode: String
        let slug: String
        let cntryNC: Int
        let cntryTC: Int
        let cntryND: Int
        let cntryTD: Int
        let cntryNR: Int
        let cntryTR: Int
        let date: String

        enum CodingKeys: String, CodingKey {
            case cntry = "Country"
            case ccode = "CountryCode"
            case slug = "Slug"
            case cntryNC = "NewConfirmed"
            case cntryTC = "TotalConfirmed"
            case cntryND = "NewDeaths"
            case cntryTD = "TotalDeaths"
            case cntryNR = "NewRecovered"
            case cntryTR = "TotalRecovered"
            case date = "Date"
        }
    }
}

如图所示，API 调用和 JSON 解码的结果根据需要使用 ObserveableObject 和 @Published 发布。

在 ContentView 中，我遵循 ObservedObject 规则，只想在 UI 上显示来自 JSON 数据的数据点以确认它正在工作：

import SwiftUI
import Foundation
import Combine

struct ContentView: View {

    @ObservedObject var summary = APICall()

    var body: some View {

        Text($summary.date)

        .onAppear {
            self.summary.pullSummary()
        }
    }

    struct ContentView_Previews: PreviewProvider {
        static var previews: some View {
            ContentView()
        }
    }
}

但是...我在文本显示行收到这 2 个错误，1) Initializer 'init(_:)' requires that 'Binding<Subject>' conform to 'StringProtocol' 和 2) Value of type 'ObservedObject<APICall>.Wrapper' has no dynamic member 'date' using the key path from root type 'APICall'。

我猜测第二个错误是问题的根本原因，表明数据没有正确传递到 ContentView。

感谢任何建议。

谢谢。

Answer 1

内部属性混乱的视图模型

struct ContentView: View {

    @ObservedObject var viewModel = APICall()

    var body: some View {

        Text(viewModel.summary?.date ?? "Loading...") // << no $ sign !!!

        .onAppear {
            self.viewModel.pullSummary()
        }
    }
}