using NavigationController to switch between tabs

FirstDetailView.swift

import SwiftUI

struct FirstDetailView: View {
    @EnvironmentObject var nav: NavigationController
    var body: some View {
        VStack {
        Text("show me the details")
            Button(action: {
                self.nav.selection = 1
            }) {
                Text("get me to second section")
            }
        }
    }
}