nested-navigation.swift

/*

 I expect the following to be printed from running this playground 
 and drilling down to the child view:

 nextIsActive true
 childIsActive false
 ------------
 nextIsActive true
 childIsActive true

 But instead I get:

 nextIsActive true
 childIsActive false
 ------------
 nextIsActive true
 childIsActive true
 ------------
 nextIsActive false
 childIsActive true
 ------------

 Notice that both booleans switch to true, but then nextIsActive 
 switches to false.

 */

import PlaygroundSupport
import SwiftUI

class AppState: ObservableObject {
  @Published var nextIsActive = false {
    didSet {
      print("nextIsActive", nextIsActive)
      print("childIsActive", childIsActive)
      print("------------")
    }
  }
  @Published var childIsActive = false {
    didSet {
      print("nextIsActive", nextIsActive)
      print("childIsActive", childIsActive)
      print("------------")
    }
  }
}

struct GrandView: View {
  @ObservedObject var state = AppState()

  var body: some View {
    NavigationView {
      VStack {
        Text("Grand")
        NavigationLink(
          destination: NextView(state: self.state),
          isActive: self.$state.nextIsActive
        ) {
          Text("go to next view")
        }
      }
    }
  }
}

struct NextView: View {
  @ObservedObject var state: AppState

  var body: some View {
    VStack {
      Text("Next")
      NavigationLink(
        destination: Text("Child"),
        isActive: self.$state.childIsActive
      ) {
        Text("go to child view")
      }
    }
  }
}

PlaygroundPage.current.setLiveView(GrandView())