从公共 API 获取 JSON 以在 SwiftUI 的列表视图中呈现

Question

我正在尝试从Rest Api获取数据以在SwiftUI的列表视图中下载和呈现。 我想我设法让JSON下载并正确分配给所有相关的结构，但是当我去构建它时，模拟器的列表视图中没有显示任何内容。

我什至不确定我是否需要在那里拥有 ' Enum CodingKeys 。

谁能指出我可能出错的地方？

import Foundation
import SwiftUI
import Combine


struct ContentView: View {
    @ObservedObject var fetcher = LaunchDataFetcher()

    var body: some View {
        VStack {
            List(fetcher.launches) { launch in
                VStack (alignment: .leading) {
                    Text(launch.mission_name)
                    Text(launch.details)
                        .font(.system(size: 11))
                        .foregroundColor(Color.gray)
                }
            }
        }
    }
}

public class LaunchDataFetcher: ObservableObject {

    @Published var launches = [launch]()
    init(){
        load()
    }

    func load() {
        let url = URL(string: "https://api.spacexdata.com/v3/launches")!
        URLSession.shared.dataTask(with: url) {(data,response,error) in
            do {
                if let d = data {
                    let decodedLists = try JSONDecoder().decode([launch].self, from: d)
                    DispatchQueue.main.async {
                        self.launches = decodedLists
                    }
                }else {
                    print("No Data")
                }
            } catch {
                print ("Error")
            }

        }.resume()

    }
}

struct launch: Codable {
    public var flight_number: Int
    public var mission_name: String
    public var details: String

    enum CodingKeys: String, CodingKey {
           case flight_number = "flight_number"
           case mission_name = "mission_name"
           case details = "details"
        }
}

// Now conform to Identifiable
extension launch: Identifiable {
    var id: Int { return flight_number }
}


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

Answer 1

首先，我尝试找出您的代码中的哪个错误，并识别某处响应数据的launch.details为空。 这样我就可以将此属性标记为 Optional 并且它可以工作。

有关更多详细信息，您可以参考以下代码：

struct launch: Codable {
    public var flight_number: Int
    public var mission_name: String
    public var details: String?

    enum CodingKeys: String, CodingKey {
           case flight_number = "flight_number"
           case mission_name = "mission_name"
           case details = "details"
        }
}

在 catch 行，获取错误消息以确切了解发生了什么

func load() {
        let url = URL(string: "https://api.spacexdata.com/v3/launches")!
        URLSession.shared.dataTask(with: url) {(data,response,error) in
            do {
                if let d = data {
                    let decodedLists = try JSONDecoder().decode([launch].self, from: d)
                    DispatchQueue.main.async {
                        print(decodedLists)
                        self.launches = decodedLists
                    }
                }else {
                    print("No Data")
                }
            } catch let parsingError {
                print ("Error", parsingError)
            }

        }.resume()
    }

希望这有帮助！

Answer 2

控制台中有任何消息吗？ 我认为您需要在 .plist 中添加 NSAppTransportSecurity>NSAllowsArbitraryLoads>YES

传输安全阻止了明文 HTTP

Answer 3

在 Trai Nguyen 的帮助下，我设法让模拟器显示数据。

我所缺少的只是确保名为“详细信息”的变量具有可选属性（通过添加“？”） - 如下所示：

 public var details: String?

然后确保当我在视图中呈现文本时，如果返回为空，我必须给它一个值以插入 - 像这样：

Text(launch.details ?? "No Data Found")

这是对我有用的完整代码：

import Foundation
import SwiftUI
import Combine


struct ContentView: View {
    @ObservedObject var fetcher = LaunchDataFetcher()

    var body: some View {
        VStack {
            List(fetcher.launches) { launch in
                VStack (alignment: .leading) {
                    Text(launch.mission_name)

                    Text(launch.details ?? "No Data Found")
                        .font(.system(size: 11))
                        .foregroundColor(Color.gray)
                }
            }
        }
    }
}


public class LaunchDataFetcher: ObservableObject {

    @Published var launches = [launch]()

    init(){
        load()
    }

    func load() {
        let url = URL(string: "https://api.spacexdata.com/v3/launches")!
        URLSession.shared.dataTask(with: url) {(data,response,error) in
            do {
                if let d = data {
                    let decodedLists = try JSONDecoder().decode([launch].self, from: d)
                    DispatchQueue.main.async {
                        print(decodedLists)
                        self.launches = decodedLists
                    }
                }else {
                    print("No Data")
                }
            } catch let parsingError {
                print ("Error", parsingError)
            }

        }.resume()
    }
}

struct launch: Codable {
    public var flight_number: Int
    public var mission_name: String
    public var details: String?
}

/// Now conform to Identifiable
extension launch: Identifiable {
    var id: Int { return flight_number }
}


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