import SwiftUI

class CounterModel: ObservableObject {
  @Published var count = 0
  func increment() { count += 1 }
}

struct ChildView: View {
  @ObservedObject var model: CounterModel
  var body: some View {
    HStack {
      Text("Count: \(model.count)")
      Button("Inc") { model.increment() }
    }
  }
}

struct ParentView: View {
  @StateObject private var model = CounterModel()
  var body: some View {
    VStack(spacing: 12) {
      ChildView(model: model)
    }
    .padding()
  }
}

                    

import SwiftUI

struct ContentView: View {
  var body: some View {
    ParentView()
  }
}

                    

import SwiftUI

@main
struct MyApp: App {
  var body: some Scene {
    WindowGroup { ContentView() }
  }
}