SwiftUI Updating Environment and Sheets

ContentView.swift

//
//  ContentView.swift
//  EnvTest
//
//  Created by Kai Oelfke on 03.02.23.
//

import SwiftUI

struct Inner: View {
  @Environment(\.myCustomValue) private var value
  var body: some View {
    Text("Inner Child: \(value)")
      .transformEnvironment(\.myCustomValue, transform: { print("inner", $0) })
  }
}

struct SheetView: View {
  @Environment(\.myCustomValue) private var value
  var body: some View {
    Text("Child Sheet: \(value)")
  }
}

struct ContentView: View {
  @State private var showSheet = true
  var body: some View {
    VStack {
      Inner()
      Button("Show sheet") {
        showSheet = true
      }
      .sheet(isPresented: $showSheet) {
        SheetView()
          .transformEnvironment(\.myCustomValue, transform: { print("sheet", $0) })
        // Applying it inside makes updates available.
        // .modifier(MyModifier())
        //.presentationDetents([.fraction(0.1)]) // to see both values
      }
    }
    .modifier(MyModifier())
  }
}

struct MyModifier: ViewModifier {
  @State var value = "Initial value from modifier"
  @State var color: Color = .primary
  func body(content: Content) -> some View {
    content
    .onAppear {
      Task {
        while true {
          try? await Task.sleep(nanoseconds: NSEC_PER_SEC)
          value = "value \((0...100).randomElement()!)"
          color = [Color.blue, .red, .yellow, .orange, .green].randomElement()!
        }
      }
    }
    .myCustomValue(value)
    .foregroundColor(color)
  }
}

private struct MyEnvironmentKey: EnvironmentKey {
  static let defaultValue: String = "Default value from Environment Key"
}

extension EnvironmentValues {
  var myCustomValue: String {
    get { self[MyEnvironmentKey.self] }
    set { self[MyEnvironmentKey.self] = newValue }
  }
}

extension View {
  func myCustomValue(_ myCustomValue: String) -> some View {
    environment(\.myCustomValue, myCustomValue)
  }
}

struct ContentView_Previews: PreviewProvider {
  static var previews: some View {
    ContentView()
  }
}