EnvironmentObject not injected for .navigationDestination

Question

Consider code

@EnvironmentObject var navModel: NavigationModel
var body: some View {
    someView
       .navigationDestination(for: ImageModel.self) { imageModel in
                ImageDetailedView(image: imageModel)
                    .environmentObject(navModel)   //this is required 
       }
}

Is navigation not considered a child of the view? And if so, is it normal to keep throwing around environemntObjects around the navigation stack?

import Combine
import SwiftUI

enum Destination {
    case firstPage
    case secondPage
}

enum Category: Int, Hashable, CaseIterable, Identifiable, Codable {
    case dessert
    case pancake
    case salad
    case sandwich
    
    var id: Int { rawValue }
    
    var localizedName: LocalizedStringKey {
        switch self {
        case .dessert:
            return "Dessert"
        case .pancake:
            return "Pancake"
        case .salad:
            return "Salad"
        case .sandwich:
            return "Sandwich"
        }
    }
}

@available(iOS 16.0, *)
class Coordinator3: ObservableObject {
    @Published var path = NavigationPath()
    
    func gotoHomePage() {
        path.removeLast(path.count)
    }
    
    func tapOnEnter() {
        path.append(Destination.firstPage)
    }
    
    func tapOnFirstPage() {
        path.append(Destination.secondPage)
    }
    
    func tapOnSecondPage() {
        path.removeLast()
    }
    
    func test() {
        path.removeLast(path.count)
        path.append(2)
    }
}

class Test :ObservableObject {
    var name = "test"
}

@available(iOS 16.0, *)
struct SplitTestView: View {
    @State var selectedCategory: Category?
    var categories = Category.allCases
    @ObservedObject var coordinator = Coordinator3()
    @StateObject var test = Test()
    
    var body: some View {
        NavigationSplitView {
            List(categories, selection: $selectedCategory) { category in
                NavigationLink(category.localizedName, value: category)
            }
        } detail: {
            NavigationStack(path: $coordinator.path) {
                switch selectedCategory {
                case .dessert:
                    Text(selectedCategory!.localizedName)
                case .pancake:
                    VStack {
                        Text("Navigation stack")
                            .padding()
                        NavigationLink("NavigationLink to enter first page", value: Destination.firstPage)
                            .padding()
                        NavigationLink("NavigationLink to enter second page", value: Destination.secondPage)
                            .padding()
                    }
                    .navigationDestination(for: Destination.self) { destination in
                        if destination == .firstPage {
                            FirstPage()
                        } else {
                            Text(
                                "SecondPage()"
                            )
                        }
                    }
                case .salad: Text(selectedCategory!.localizedName)
                case .sandwich: Text(selectedCategory!.localizedName)
                case .none: Text("hi")
                }
            }.environmentObject(test)
        }
    }
}

@available(iOS 16.0, *)
struct SplitTestView_Previews: PreviewProvider {
    static var previews: some View {
        SplitTestView()
    }
}
struct FirstPage: View {
    @EnvironmentObject var test: Test
    var body: some View {
        Text("First Page \(test.name)")
    }
}

Answer 1

This is why MREs are important that is why I mentioned it in my first comment, you introduced NavigationSplitView.

Scenario 1

If you are using NavigationSplitView you have to inject the EnvironmentObject to the NavigationSplitView.

NavigationSplitView{
    /*other stuff that includes a navigationDestination*/
}.environmentObject(navModel)

Scenerio 2

When working with just NavigationStack you have to inject on the NavigationStack

NavigationStack{
    /*other stuff that includes a navigationDestination*/
}.environmentObject(navModel)

Scenerio 3 - Deprecated

When working with just NavigationView you have to inject on the NavigationView

NavigationView{
    /*other stuff that includes a NavigationLink*/
}.environmentObject(navModel)

Your Sample

Just move the injection code one line down.

import Combine
import SwiftUI

@available(iOS 16.0, *)
struct SplitTestView: View {
    @State var selectedCategory: Category?
    var categories = Category.allCases
    @StateObject var coordinator = Coordinator3() //<-- Switch to StateObject
    @StateObject var test = Test()
    
    var body: some View {
        NavigationSplitView {
            List(categories, selection: $selectedCategory) { category in
                NavigationLink(category.localizedName, value: category)
            }
        } detail: {
            NavigationStack(path: $coordinator.path) {
                switch selectedCategory {
                case .dessert:
                    Text(selectedCategory!.localizedName)
                case .pancake:
                    VStack {
                        Text("Navigation stack")
                            .padding()
                        NavigationLink("NavigationLink to enter first page", value: Destination.firstPage)
                            .padding()
                        NavigationLink("NavigationLink to enter second page", value: Destination.secondPage)
                            .padding()
                    }
                    .navigationDestination(for: Destination.self) { destination in
                        if destination == .firstPage {
                            FirstPage()
                        } else {
                            Text(
                                "SecondPage()"
                            )
                        }
                    }
                case .salad: Text(selectedCategory!.localizedName)
                case .sandwich: Text(selectedCategory!.localizedName)
                case .none: Text("hi")
                }
            }
        }.environmentObject(test) //<<--- Add to the NavigationSplitView - The NavigationLink's are presenting in a separate column than the Stack, the only thing they share is the split view.
    }
}
enum Destination {
    case firstPage
    case secondPage
}

enum Category: Int, Hashable, CaseIterable, Identifiable, Codable {
    case dessert
    case pancake
    case salad
    case sandwich
    
    var id: Int { rawValue }
    
    var localizedName: LocalizedStringKey {
        switch self {
        case .dessert:
            return "Dessert"
        case .pancake:
            return "Pancake"
        case .salad:
            return "Salad"
        case .sandwich:
            return "Sandwich"
        }
    }
}

@available(iOS 16.0, *)
class Coordinator3: ObservableObject {
    @Published var path = NavigationPath()
    
    func gotoHomePage() {
        path.removeLast(path.count)
    }
    
    func tapOnEnter() {
        path.append(Destination.firstPage)
    }
    
    func tapOnFirstPage() {
        path.append(Destination.secondPage)
    }
    
    func tapOnSecondPage() {
        path.removeLast()
    }
    
    func test() {
        path.removeLast(path.count)
        path.append(2)
    }
}

class Test :ObservableObject {
    var name = "test"
}



@available(iOS 16.0, *)
struct SplitTestView_Previews: PreviewProvider {
    static var previews: some View {
        SplitTestView()
    }
}
struct FirstPage: View {
    @EnvironmentObject var test: Test
    var body: some View {
        Text("First Page \(test.name)")
    }
}

Addl Info

In the Migration Guide apple talks about the differences between the 2 types.

https://developer.apple.com/documentation/swiftui/migrating-to-new-navigation-types

They call the inside of the NavigationStack "content"

NavigationStack {
    /* content */
}

And the inside of the NavigationSplitView "columns"

NavigationSplitView {
    /* column 1 */
} content: {
    /* column 2 */
} detail: {
    /* column 3 */
}

In their respective setups the "columns" and "content" only share the NavigationSplitView or NavigationStack respectively with the NavigationLinks/navigationDestination.

A NavigationLink inside NavigationStack that is inside NavigationSplitView presents in its own column.

The injection should always happen at the uppermost shared View.