ContentView with NavigationController in the environment

MainContentView.swift

import SwiftUI

struct ContentView: View {
    
    @EnvironmentObject var nav: NavigationController
   
    var body: some View {
     // binding TabView selection to NavigationController
        TabView(selection: self.$nav.selection){
            FirstView()
                .tabItem {
                    Text("First")
            }.tag(0)
            
            Text("Second View")
                .font(.title)
                .tabItem {
                    Text("Second")
                    
            }.tag(1)
        }
    }
}

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

struct FirstView: View {
    @EnvironmentObject var nav: NavigationController
    var body: some View {
        NavigationView {
            VStack {
                Text("Main view")
                    .font(.title)
                // binding NavigationLink isAcitve to NavigationController
                NavigationLink(destination: FirstDetailView(), isActive: self.$nav.detailIsShown) {
                    Text("show me the details")
                }
            }
        }.navigationViewStyle(StackNavigationViewStyle())
    }
}