MacOS combine swiftui example

ContentView.swift

import SwiftUI
import Combine

struct Todo:Codable {
    let userId:Int
    let id:Int
    let title:String
    let completed:Bool
}


class StaticPublisherMaker {
    
    static func makeNetworkPublisher() -> AnyPublisher<String,Error> {
        print("Make publisher")
        let url = URL(string:"https://jsonplaceholder.typicode.com/todos/\((1..<5).randomElement()!)")!
        var request = URLRequest(url: url)
        request.httpMethod = "GET"
        request.cachePolicy = .reloadIgnoringLocalAndRemoteCacheData
        URLSession.shared.configuration.urlCache = .none
        
        return URLSession.shared
            .dataTaskPublisher(for: request)
            .map(\.data)
            .decode(type: Todo.self, decoder: JSONDecoder())
            .print()
            .map(\.title)
            .eraseToAnyPublisher()
    }
    
}


class HelperClass:ObservableObject {
    @Published var output:String = "not set"
    
    var cancellable:AnyCancellable? = nil
    
    var isOn:Bool = false
   
    init() {
        print("Making helper class")
    }

    deinit {
        print("De init")
    }
    
    func getBinding() -> Binding<Bool> {
        return Binding<Bool>(get: {
            print("Getting",self.isOn)
            return self.isOn
        }, set: {
            print("Setting",self.isOn,$0)
            self.isOn = $0
        })
    }
    


    func goDo() {
        self.cancellable = StaticPublisherMaker.makeNetworkPublisher().replaceError(with: "error").receive(on: DispatchQueue.main).assign(to: \.output, on: self)
    }
}

extension View {
    func eraseToAnyView() -> AnyView {
        return AnyView(self)
    }
}


struct ContentView: View {
    
    @State var showSubView = false
    
    var body: some View {
        VStack {
            SubView()
            Spacer()
        }.frame(width: 300, height: 200)
    }
}

struct SubView: View {

    @ObservedObject var helper = HelperClass()
    
    var body: some View {
        VStack {
            Button(action: {
                self.helper.goDo()
            }) {
                Text("Fetch!")
            }
            Text("Output: \(self.helper.output)")
                    .frame(maxWidth: .infinity, maxHeight: .infinity)
        }

    }
    
}



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