viewmodel.swift

import SwiftUI

@MainActor class ViewModel: ObservableObject {
    private let events = AsyncStream<AwaitableEvent>.makeStream()

    struct AwaitableEvent {
        let event: Event
        let continuation: CheckedContinuation<Void, Never>
    }

    enum Event {
        case loadSomeData
        case exit
    }

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

    init() {
        bind()
    }

    @Published var posts: [Post] = []

    func send(_ event: Event) async {
        return await withCheckedContinuation { continuation in
            let awaitable = AwaitableEvent(
                event: event,
                continuation: continuation
            )

            events.continuation.yield(awaitable)
        }
    }

    func bind() {
        Task {
            for await awaitable in self.events.stream {
                switch awaitable.event {
                case .loadSomeData:
                    try? await self.loadDataMainActor()
                case .exit:
                    exit(0) // hoorayy!
                }
                
                
                awaitable.continuation.resume()
            }
        }
    }

    func loadDataMainActor() async throws{
        posts = []
        let url = URL(string: "https://jsonplaceholder.typicode.com/posts")!
        let (data, _) = try await URLSession.shared.data(from: url)
        do {
            posts = try JSONDecoder().decode([Post].self, from: data)
        } catch {
            print("error=\(error)")
        }
        print("posts.count=\(posts.count)")
    }
}

struct ContentView: View {
    @StateObject var viewModel: ViewModel

    var body: some View {
        List(viewModel.posts) { row in
            Text("Row \(row)")
        }
        .refreshable {
            print("[aaa] Refreshable.start")
            await viewModel.send(.loadSomeData)
            print("[aaa] Refreshable.end")
        }
    }
}