ContentView.swift

//
//  ContentView2.swift
//  MVVM
//
//  Created by Ivan Ornes on 10/8/22.
//

import SwiftUI

class Model: ObservableObject { // Rich domain
    @Published var counter: Int = 0
    
    func increment() {
        counter += 1
    }
}

// <GrandChildView: View> Avoids requiring AnyView
struct ChildView<GrandChildView: View>: View { 
    
    private let vm: ChildViewModel
    private let grandChildView: GrandChildView
    
    init(vm: ChildViewModel, grandChildView: GrandChildView) {
        self.vm = vm
        self.grandChildView = grandChildView
    }
    
    var body: some View {
        VStack {
            grandChildView
        }
    }
}

class GrandChildViewModel: ObservableObject {
    
    private let model: Model
    
    init(model: Model) {
        self.model = model
    }
    
    func increment() {
        model.increment()
    }
}

struct GrandChildView: View {
    
    private let vm: GrandChildViewModel
    
    init(vm: GrandChildViewModel) {
        self.vm = vm
    }
    
    var body: some View {
        VStack {
            Button("Increment from GrandChildView") {
                vm.increment()
            }
        }
    }
}

class ContentViewModel: ObservableObject {
    
    private let model: Model

    @Published var counter: String = "0"
    
    init(model: Model) {
        self.model = model
        _ = model.$counter.sink {
            // Adapt domain model to what the UI should show
            self.counter = "\($0)"
        }
    }
    
    func increment() {
        model.increment()
    }
}

class ChildViewModel: ObservableObject {
    
    private let model: Model
    
    init(model: Model) {
        self.model = model
    }
}

struct ContentView<ChildView: View>: View {

    let vm: ContentViewModel
    let childView: ChildView
    
    var body: some View {
        VStack {
            // Follow the Demeter law, do not go too deep in the dependency dependencies
            // Uses the formatted counter of the view model
            Text(vm.counter) 
                .font(.largeTitle)
            Button("Increment from ContentView") {
                vm.increment()
            }
            childView
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    
    static var previews: some View {
        let model = Model()
        let grandChildView = GrandChildView(vm: GrandChildViewModel(model: model))
        let childView = ChildView(vm: ChildViewModel(model: model), grandChildView: grandChildView)
        ContentView(vm: ContentViewModel(model: model), childView: childView)
    }
}

LearnApp.swift

//
//  MVVMApp.swift
//  MVVM
//
//  Created by Ivan Ornes on 10/8/22.
//

import SwiftUI

@main
struct MVVMApp: App {
    
    @StateObject private var model = Model()
    
    var body: some Scene {
        WindowGroup { // App composition
            let grandChildView = GrandChildView(vm: GrandChildViewModel(model: model))
            let childView = ChildView(vm: ChildViewModel(model: model), grandChildView: grandChildView)
            ContentView(vm: ContentViewModel(model: model), childView: childView)
        }
    }
}