Custom @Environment Objects (aka Apple DI Container)

README.md

Trying the trick that @azamsharp shared here and here

In Action:

Mocked	Real

ContentView.swift

import SwiftUI

struct Post: Decodable, Identifiable {
    let id: Int
    let title: String
}

protocol HttpClientProtocol {
    func fetchPosts() async throws -> [Post]
}

class HttpClient: HttpClientProtocol {
    
    func fetchPosts() async throws -> [Post] {
        let url = URL(string: "https://jsonplaceholder.typicode.com/posts")!
        let (data, _) = try await URLSession.shared.data(from: url)
        return try JSONDecoder().decode([Post].self, from: data)
    }
}

class MockedHttpClient: HttpClientProtocol {
    func fetchPosts() async throws -> [Post]{
        return [Post(id: 1, title: "Post #1"), Post(id: 2, title: "Post #2")]
    }
}


struct HttpClientEnvironmentKey: EnvironmentKey {
    static var defaultValue: HttpClientProtocol = HttpClient()
}

extension EnvironmentValues {
    var httpClient: (HttpClientProtocol) {
        get { self[HttpClientEnvironmentKey.self] }
        set { self[HttpClientEnvironmentKey.self] = newValue }
    }
}

struct ContentView: View {
    @Environment(\.httpClient) private var httpClient

    @State private var posts: [Post] = []
    
    var body: some View {
        VStack {
            List(posts) { post in
                Text(post.title)
            }.task {
                do {
                    posts = try await httpClient.fetchPosts()
                } catch {
                    print(error.localizedDescription)
                }
            }
        }
    }
}

#Preview {
    ContentView()
        .environment(\.httpClient, MockedHttpClient())
}