This sample shows Observable object instances with `@Observable and @State` are created many times when a view that has the property is evaluated. So avoid heavy initializations on the Observable classes.

sample-vm-problem.swift

//
//  ObservableTwiceInitProblemTestApp.swift
//  ObservableTwiceInitProblemTest
//
//  Created by Yasuhito Nagatomo on 2024/05/20.
//
//  Modified christianselig/sample-view-model-init.swift
//  https://gist.github.com/christianselig/d88b1a4d1989b973689ae62d4691162f
//
//  This sample shows Observable object instances with `@Observable and @State`
//  are created many times when a view that has the property is evaluated.
//  So avoid heavy initializations on the Observable classes.

import SwiftUI

@main
struct WindowPresentationFunApp: App {
    @State var appState = AppState()

    var body: some Scene {
        WindowGroup {
            InitialView(appState: appState)
        }
    }
}

struct InitialView: View {
    let appState: AppState
    @State private var showing = false

    var body: some View {
        Button(action: { showing.toggle() }, label: { Text("Tap Me")})
            .sheet(isPresented: $showing) {
                RootView(appState: appState)
            }
    }
}

struct RootView: View {
    let appState: AppState

    var body: some View {
        VStack {
            Text("Swipe down to close").padding()

            SpecialView()

            Button(action: { appState.show.toggle() }) {
                Text("Change the show flag").padding()
            }

            Text("Show flag: " + (appState.show ? "True" : "False")).padding()
        }
    }
}

struct SpecialView: View {
    @State private var viewModel = ViewModel()

    var body: some View {
        let _ = print("SpecialView will be evaluated.")
        Text("Special stuff, VM's MyID: \(viewModel.myID)")
    }
}

@Observable class AppState {
    var show: Bool = false
}

@Observable class ViewModel {
    let myID = UUID()

    // This cannot be `lazy` when using @Observable
    let attribute1: Int = {
        print("Heavy Calculation #1 ...")
        return 0
    }()

    init() {
        print("✅ View model was inited ID: \(myID)")
    }

    deinit {
        print("❌ View model was deinited ID: \(myID)")
    }
}