ContentView.swift

//
//  ContentView.swift
//  Learn
//
//  Created by Mohammad Azam on 6/29/22.
//

import SwiftUI

class AppState: ObservableObject {
    
    @Published var value: Int = 0
    @Published var isAuthenticated: Bool = false
    
    var counterState = CounterState()
    var authState = AuthState()
}

class CounterState: ObservableObject {
    @Published var value: Int = 0
}

class AuthState: ObservableObject {
    @Published var isAuthenticated: Bool = false
}

protocol IncrementCounterViewModelProtocol {
    func increment()
}

protocol DisplayCounterViewModelProtocol {
    var counter: Int { get }
}

class IncrementCounterViewModel: IncrementCounterViewModelProtocol {
    
    var appState: AppState
    
    init(appState: AppState) {
        self.appState = appState
    }
    
    func increment() {
        appState.value += 1
    }
    
}

class DisplayCounterViewModel: DisplayCounterViewModelProtocol {
    
   private var appState: AppState
    
    init(appState: AppState) {
        self.appState = appState
    }
    
    var counter: Int {
        appState.value
    }
    
}

struct DisplayCounterView: View {
    
    let vm: DisplayCounterViewModelProtocol
    
    init(vm: any DisplayCounterViewModelProtocol) {
        self.vm = vm
    }
    
    var body: some View {
        let _ = Self._printChanges()
        Text("\(vm.counter)")
    }
}

struct IncrementCounterView: View {
    
    let vm: IncrementCounterViewModelProtocol
    
    init(vm: any IncrementCounterViewModelProtocol) {
        self.vm = vm
    }
    
    var body: some View {
        let _ = Self._printChanges()
        VStack {
            Button("Increment") {
                vm.increment()
            }
        }
    }
}

struct FancyCounterView: View {
    
    let counter: Int
    
    var body: some View {
        Text("\(counter)")
    }
}



struct FancyView: View {
    
    let vm: FancyViewModel
    
    var body: some View {
        FancyCounterView(counter: vm.counter)
    }
}

class FancyViewModel {
    
    private var appState: AppState
     
    init(appState: AppState) {
        self.appState = appState
    }
    
    var counter: Int {
        self.appState.value
    }
}

struct GrandChildView: View {
    
    @EnvironmentObject var counterState: CounterState
    
    var body: some View {
        let _ = Self._printChanges()
        VStack {
            Text("GRAND CHILD VIEW")
            Text("\(counterState.value)")
        }
    }
}

struct ChildView: View {
    var body: some View {
        GrandChildView()
    }
}

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

struct AuthView: View {
    
    @EnvironmentObject var authState: AuthState
    
    var body: some View {
        VStack {
            Text(authState.isAuthenticated ? "AUTHENTICATED": "NOT AUTHENTICATED")
            Button("Toggle Auth") {
                authState.isAuthenticated.toggle()
            }
        }
    }
}

struct ContentView: View {
    
    @EnvironmentObject var appState: AppState
    
    var body: some View {
        let _ = Self._printChanges()
        VStack {
            DisplayCounterView(vm: DisplayCounterViewModel(appState: appState))
            IncrementCounterView(vm: IncrementCounterViewModel(appState: appState))
            ParentView()
            AuthView()
        }
    }
}

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

LearnApp.swift

//
//  LearnApp.swift
//  Learn
//
//  Created by Mohammad Azam on 6/29/22.
//

import SwiftUI

@main
struct LearnApp: App {
    
    let appState = AppState()
    
    var body: some Scene {
        WindowGroup {
            ContentView()
                .environmentObject(appState)
                .environmentObject(appState.counterState)
                .environmentObject(appState.authState)
        }
    }
}