SwiftUI 2.0 App crash when Picker selectedValue changed - xcode

Question

Here is my sample code:
import SwiftUI
final class ViewModel: ObservableObject {
#Published var countries: [Country?] = [
Country(id: 0, name: "country1", cities: ["c1 city1", "c1 city2", "c1 city3"]),
Country(id: 1, name: "country2", cities: ["c2 city1", "c2 city2", "c2 city3"]),
Country(id: 2, name: "country3", cities: ["c3 city1", "c3 city2", "c3 city3"])
]
}
struct ContentView: View {
#ObservedObject var viewModel = ViewModel()
#State private var selectedCountry: Country? = nil
#State private var selectedCity: String? = nil
var body: some View {
VStack {
Picker("", selection: $selectedCountry) {
ForEach(viewModel.countries, id: \.self) { country in
Text(country!.name).tag(country)
}
}
.pickerStyle(SegmentedPickerStyle())
Text(selectedCountry?.name ?? "no selection")
if selectedCountry != nil {
Picker("", selection: $selectedCity) {
ForEach(selectedCountry!.cities, id: \.self) { city in
Text(city!).tag(city)
}
}
.pickerStyle(SegmentedPickerStyle())
Text(selectedCity ?? "no selection")
}
}
.padding()
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
struct Country: Codable, Hashable, Identifiable {
var id: Int
var name: String
var cities: [String?]
}
It works at first but when select a country then select another country then go back to the first choice it crashes,
I am using latest Xcode beta I don't know if it is the cause or my approach is wrong.

Answer 1

The problem is in cached binding. We need to recreate picker if source of data changed.
Find below a fix. Tested with Xcode 12.4 / iOS 14.4
if selectedCountry != nil {
Picker("", selection: $selectedCity) {
ForEach(selectedCountry!.cities, id: \.self) { city in
Text(city!).tag(city)
}
}
.pickerStyle(SegmentedPickerStyle())
.id(selectedCountry!) // << here !!
Text(selectedCity ?? "no selection")
}