@EnvironmentObject doesn't work well through navigationLink

Question

I use my @EnvironmentObject to let my TeamData can use by different but it doesn't work well. When I go to another view by navigationLink in List, it's fine. When I tap a button to the same View, it crashed..
I think I put something wrong. Can somebody help for this issue? Is it mean I need to add @EnvironmentObject at the NavigationView first so that I can use it? Thanks

Demo: https://youtu.be/-iRadrHd94c

import SwiftUI

struct GameRecordListView: View {
@EnvironmentObject var teamResult : TeamResult

@State var hint : String = ""
@State var successRegistration : Bool = false
@State var sheetPresented: Bool = false
var body: some View {
     VStack{

        List(0 ..< 12){ item in
            NavigationLink(destination: GameDetailRecordView()){   <-this works well
                Text("444")

            }
        }
        VStack{
            Spacer()
            HStack{
                Spacer()
                NavigationLink(destination: GameDetailRecordView())  <-this doesn't works well and crashed
                {
                    Image(systemName: "pencil.circle")
                        .resizable()
                        .frame(width: 35, height: 35)
                        .padding(12)
                        .background(Color.blue)
                        .foregroundColor(Color.white)
                        .clipShape(Circle())

                }
            }.padding(15)

        }

     }.onAppear(perform: {
        print("teamResult:\(self.teamResult.groupID):\(self.teamResult.groupName)")
     })
}
}

I create a enviromentObject in this View

import SwiftUI
import SwiftyJSON

struct TeamDetail: View {
@EnvironmentObject var teamResult : TeamResult
//    @ObservedObject var teamResult: TeamResult
var roles = ["GameRecord", "Schedule", "Money", "Member"]
@State var show = false
@State private var selectedIndex = 0
var body: some View {
    ZStack{
        VStack {
            Picker(selection: $selectedIndex, label: Text("")) {
                ForEach(0..<roles.count) { (index) in
                    Text(self.roles[index])
                }
            }
            .pickerStyle(SegmentedPickerStyle())

            HStack{
                containedView()

            }
            Spacer()

            }


        }.navigationBarTitle(teamResult.groupName)
        .onAppear(perform:{

        })
}



//select different view by selectedIndex
func containedView() -> AnyView {
   switch selectedIndex {
   case 0:
       return AnyView(
            GameRecordListView().environmentObject(teamResult)   <-create environmentObject here
       )

   case 1:

      return AnyView(Text("")
           .padding(30))


   case 2:
      return AnyView(
        BookkeepingView().environmentObject(teamResult)

    )


   default:
    return AnyView(
        TeamMemberListView().environmentObject(teamResult))
}

}
}

The view I use the @EnviromentObject

import SwiftUI

struct GameDetailRecordView: View {
  @EnvironmentObject var teamResult : TeamResult
  var body: some View {
     Text("ID:\(teamResult.groupID)Name:\(teamResult.groupName)")
  }
}

Error message:

Fatal error: No ObservableObject of type TeamResult found.
A View.environmentObject(_:) for TeamResult may be missing as an ancestor of this view.: file /BuildRoot/Library/Caches/com.apple.xbs/Sources/Monoceros_Sim/Monoceros-39.4.3/Core/EnvironmentObject.swift, line 55
2020-01-20 01:14:58.466655+0800 Fitness(SwiftUI)[49035:4851345] Fatal error: No ObservableObject of type TeamResult found.
A View.environmentObject(_:) for TeamResult may be missing as an ancestor of this view.: file /BuildRoot/Library/Caches/com.apple.xbs/Sources/Monoceros_Sim/Monoceros-39.4.3/Core/EnvironmentObject.swift, line 55

Corrinecorrinne

Answer 1

try adding environmentObject on the view in the NavigationLink

 NavigationLink(destination: GameDetailRecordView().environmentObject(teamResult))

Turnstile

Hi, I use this method and this can work. But I want to know why the NavigationLink in the list doesn't need to add .environmentObject(teamResult) and another need to add .environmentObject(teamResult). Is it means that NavigationLink create a new environment? I think all View below GameRecordListView().environmentObject(teamResult) can use the @environmentObject teamResult at all. – Corrinecorrinne

Hi @frank61003, have you managed to figure out why this happens? I am in the same situation. – Expostulatory

It appears that all environmentObjects are not passed down when NavigationLink is "created" dynamically at runtime. In those cases, you have to supply environmentObjects again. – Soemba

interesting gotcha...probably a bug – Moorfowl

Answer 2

Is it mean I need to add @EnvironmentObject at the NavigationView first so that I can use it?

Correct, NavigationLinks cannot pass environment objects onto their destinations; only the NavigationView can do that, since it owns the view hierarchy.

So, if somewhere in your code you did something like this:

NavigationView {
  ContentView()
    .environmentObject(teamResult)
}

You need to change it to:

NavigationView {
  ContentView()
}
.environmentObject(teamResult)

Then the ContentView will be able to receive the @EnvironmentObject, as well as any destination view of a NavigationLink therein, without needing to use the environmentObject(_:) view modifier on each destination view.

Opposite

This should be the top answer. It accurately addresses the question of how to make an environment object work properly, as an environment object should. If I wanted to pass the environment object explicitly through all my navigation links, I would just make it an explicit @Binding on the view itself. – Lycian