ContentView.swift

struct ContentView: View {
  @StateObject var viewModel = ViewModel()
    
  var body: some View {
    NavigationView {
      Form {
        Section {
          // …
            DateDurationPicker(
              selection: $viewModel.selection, 
              values: Array(1..<100), 
              units: DateDuration.Unit.allCases
            )
          // …
        }
      }
      .navigationTitle("Reminders")
    }
  }
}

extension ContentView {
  final class ViewModel: ObservableObject {
    @Published var selection = DateDuration(value: 1, unit: .days)
    // …
  }
}