从公共 API 获取 JSON 以在 SwiftUI 的列表视图中呈现答案

【问题标题】：Getting JSON from a public API to render in a list view in SwiftUI从公共 API 获取 JSON 以在 SwiftUI 的列表视图中呈现
【发布时间】：2019-12-03 04:29:02
【问题描述】：

我正在尝试从Rest Api 获取数据以下载并在SwiftUI 的列表视图中呈现。我想我设法让JSON 正确下载并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。

我什至不确定是否需要在其中添加“Enum CodingKeys”。

谁能指出我哪里出错了？

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()
    }
}

【问题讨论】：

如果键和结构成员具有相同的名称，则不需要 CodingKeys。如果您将结构成员命名为 camelCased 并添加 convertFromSnakeCase 键解码策略，您甚至不需要 CodingKeys。
我以为是这样。感谢您的建议。

标签： ios swiftui xcode11 swift5.1 swiftui-list

【解决方案1】：

首先，我尝试找出您的代码的哪个错误，并识别某处响应数据的launch.details为空。所以我只是将此属性标记为可选并且它可以工作。

更多细节，你可以参考下面的代码：

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"
        }
}

在捕获线，获取错误消息以准确了解发生了什么

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()
    }

希望对您有所帮助！

【讨论】：

@Lofty 给我投票吧，这会让我更有动力^_^

【解决方案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

Transport security has blocked a cleartext HTTP

【讨论】：

我不需要这样做。

【解决方案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“？”） - 就像这样：

 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 - 就像这样：

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

这是适合我的完整代码：

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()
    }
}

【讨论】：