SwiftUIでAPI呼び出しでJSONをパース&画像URLから画像を表示するサンプルコード

ContentView.swift

import SwiftUI

struct Dog: Codable, Identifiable {
    public var id: String
    public var status: String
    
    enum CodingKeys: String, CodingKey {
        case id = "message"
        case status = "status"
    }
    
    init() {
        self.id = ""
        self.status = ""
    }
}

public class DogFetcher: ObservableObject {
    @Published var dog = Dog()
    
    init() {
        load()
    }
    
    func load() {
        guard let url = URL(string: "https://dog.ceo/api/breeds/image/random") else { return }
        URLSession.shared.dataTask(with: url) { (data, response, error) in
            DispatchQueue.main.async {
                self.dog = try! JSONDecoder().decode(Dog.self, from: data!)
            }
        }.resume()
    }
}

class ImageDownloader : ObservableObject {
    @Published var downloadData: Data? = nil

    func downloadImage(url: String) {

        guard let imageURL = URL(string: url) else { return }

        DispatchQueue.global().async {
            let data = try? Data(contentsOf: imageURL)
            DispatchQueue.main.async {
                self.downloadData = data
            }
        }
    }
}

struct URLImage: View {

    let url: String
    @ObservedObject private var imageDownloader = ImageDownloader()

    init(url: String) {
        self.url = url
        self.imageDownloader.downloadImage(url: self.url)
    }

    var body: some View {
        if let imageData = self.imageDownloader.downloadData {
            let img = UIImage(data: imageData)
            return Image(uiImage: img!).resizable()
        } else {
            return Image(systemName: "arrow.2.circlepath")
        }
    }
}

struct ContentView: View {
    @ObservedObject var fetcher = DogFetcher()
    
    var body: some View {
        VStack {
            URLImage(url: fetcher.dog.id)
                .aspectRatio(contentMode: .fit)
            Spacer()
            Button(action: {
                self.fetcher.load()
            }) {
                Text("Tap")
            }
        }
        
    }
}

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