SwiftEnvironmentObjectPropagation.swift

import SwiftUI

class AppState: ObservableObject {
  @Published var counter = 0
}

struct ContentView: View {
  @EnvironmentObject var state: AppState
  @State var presentDetailsView = false
  @State var presentDetailsViewNoEnvironment = false
  
  var body: some View {
    NavigationView {
      VStack {
        Button(action: { self.state.counter += 1 }) {
          Text("Current value: \(state.counter)")
        }
        // 1: this works fine
        NavigationLink(destination: DetailsView()) {
          Text("Navigate to details")
        }
        Button(action: { self.presentDetailsView = true }) {
          Text("Present details")
        }
        Button(action: { self.presentDetailsViewNoEnvironment = true }) {
          Text("Present details w/o Environment (will crash)")
        }
      }
      .navigationBarTitle("@EnvironmentObject: Master")
      // 2: this crashes
      .sheet(isPresented: $presentDetailsViewNoEnvironment) {
        DetailsView()
      }
      // 3: (instead of 2): this works fine
      .sheet(isPresented: $presentDetailsView) {
        DetailsView().environmentObject(self.state)
      }
    }
  }
}

struct DetailsView: View {
  @EnvironmentObject var state: AppState
  
  var body: some View {
    Text("The value is \(state.counter)")
  }
  
}

Looking at the view hierarchy in the view debugger, we can see that thethis actually makes sense, as a modal screen is added to the view hierarchy in parallel to the original ContentView.

When navigating from ContentView to DetailsView using a NavigationLink, DetailsView becomes a child of ContentView:

When displaying a modal sheet using sheet(isPresented:content:), however, DetailsView will not become a child of ContentView. Instead, the hosting view will be instantiated in parallel to the originating view:

The entire project can be found here: https://github.com/peterfriese/Swift-EnvironmentObject-Demo