StateObject-vs-State.swift

import SwiftUI

class Model1: ObservableObject {
  
  static let shared = Model1()
  
  var value: Int = 0
  
  @Published
  var date: Date = Date()
  
}

struct Model2 {
  
  class Heap {
    
    static let shared = Heap()
    
    var value: Int = 0
    
    var date: Date = Date()
    
  }
  
  let heap = Heap.shared
  
  var value: Int {
    get {
      heap.value
    }
    set {
      heap.value = newValue
    }
  }
  
  var date: Date {
    get {
      heap.date
    }
    set {
      heap.date = newValue
    }
  }
  
}

let timer = Timer.publish(every: 1, on: .main, in: .common).autoconnect()

struct ContentView: View {
  
  var body: some View {
    HStack {
      SwiftUIView1()
      UIKitView1()
    }
  }
  
}

struct SwiftUIView2: View {
  
  struct Subview: View {
    
    @Binding
    var value: Int
    
    init(value: Binding<Int>) {
      self._value = value
    }
    
    var body: some View {
      Text("\(value)")
    }
    
  }
  
  @State
  var model = Model2()
  
  var body: some View {
    Subview(value: $model.value)
      .onReceive(timer) { input in
        self.model.date = input
      }
  }
  
}

class MyUIKitView2: UIView {
  
  var model = Model2()
  
  override func layoutSubviews() {
    super.layoutSubviews()
    DispatchQueue.main.asyncAfter(deadline: .now().advanced(by: .seconds(1))) {
      self.model.value += 1
      self.setNeedsLayout()
    }
  }
  
}

struct UIKitView2: UIViewRepresentable {

  func makeUIView(context: Context) -> UIView {
    MyUIKitView2()
  }
  
  func updateUIView(_ uiView: UIView, context: Context) {
    
  }

}

struct SwiftUIView1: View {
  
  struct Subview: View {
    
    @Binding
    var value: Int
    
    init(value: Binding<Int>) {
      self._value = value
    }
    
    var body: some View {
      Text("\(value)")
    }
    
  }
  
  @StateObject
  var model: Model1 = .shared
  
  var body: some View {
    Subview(value: $model.value)
      .onReceive(timer) { input in
        self.model.date = input
      }
  }

}

class MyUIKitView1: UIView {
  
  var myModel = Model1.shared
  
  override func layoutSubviews() {
    super.layoutSubviews()
    DispatchQueue.main.asyncAfter(deadline: .now().advanced(by: .seconds(1))) {
      self.myModel.value += 1
      self.setNeedsLayout()
    }
  }
  
}

struct UIKitView1: UIViewRepresentable {

  func makeUIView(context: Context) -> UIView {
    MyUIKitView1()
  }
  
  func updateUIView(_ uiView: UIView, context: Context) {
    
  }

}

#Preview {
    ContentView()
}