Some SwiftUI/Combine examples

PublishedViewModel.swift

//
//  ContentView.swift
//  Pub
//
//  Created by Ray Fix on 5/16/20.
//  Copyright © 2020 Ray Fix. All rights reserved.
//

import SwiftUI
import Combine

final class ViewModel: ObservableObject {
    
  @Published var number: CGFloat = 9
  // The manual way to do @Published
  //  {
  //    willSet {
  //      objectWillChange.send()
  //    }
  //  }
  
  // This gets synthesize by the ObservableObject protocol
  // let objectWillChange = PassthroughSubject<Void, Never>()

  var roundedNumberString: String {
    String(describing: Int(number.rounded()))
  }
  
  @Published var buzz: Int = 0
  
  var subscriptions = Set<AnyCancellable>()
  
  // View models tend to put a lot in the initializer
  init() {
    $number
      .map { Int($0.rounded()) }
      .removeDuplicates()
      .filter { $0.isMultiple(of: 5) }
      .handleEvents(receiveOutput: { value in
        // You can put a side effect in here
        print("BUZZ \(value)")
      })
      .assign(to: \.buzz, on: self)
      .store(in: &subscriptions)
  }
}


struct ContentView: View {
  
  @ObservedObject var viewModel = ViewModel()
  
  var body: some View {
    VStack {
      Slider(value: $viewModel.number, in: 1...20)
      Text(viewModel.roundedNumberString)
      Text("\(viewModel.buzz)")
    }.padding()
  }
}

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