How to change picker based on text field input - ios

Question

I'm currently trying to change the data the picker will display based on the value in the series text field. I'm not getting the picker to show up, I'm not getting any errors but I'm getting this warning "Non-constant range: not an integer range" for both the ForEach lines below.
struct ConveyorTracks: View {
#State private var series = ""
#State private var selectedMaterial = 0
#State private var selectedWidth = 0
#State private var positRack = false
let materials8500 = ["HP", "LF", "Steel"]
let widths8500 = ["3.25", "4", "6"]
let materials882 = ["HP", "LF", "PS", "PSX"]
let widths882 = ["3.25", "4.5", "6","7.5", "10", "12"]
var materials: [String] {
if series == "8500" {
return materials8500
} else if series == "882" {
return materials882
} else {
return []
}
}
var widths: [String] {
if series == "8500" {
return widths8500
} else if series == "882" {
return widths882
} else {
return []
}
}
var body: some View {
VStack(alignment: .leading) {
HStack {
Text("Series:")
TextField("Enter series", text: $series)
}.padding()
HStack {
Text("Material:")
Picker("Materials", selection: $selectedMaterial) {
ForEach(materials.indices) { index in
Text(self.materials[index])
}
}.pickerStyle(SegmentedPickerStyle())
}.padding()
HStack {
Text("Width:")
Picker("Widths", selection: $selectedWidth) {
ForEach(widths.indices) { index in
Text(self.widths[index])
}
}.pickerStyle(SegmentedPickerStyle())
}.padding()
HStack {
Text("Positive Rack:")
Toggle("", isOn: $positRack)
}.padding()
}
}
}
struct ConveyorTrack_Previews: PreviewProvider {
static var previews: some View {
ConveyorTracks()
}
}
I would like the pickers to change based on which value is input in the series text field, for both materials and width.
Perhaps pickers isn't the best choice, I am open to any suggestions.
Thanks!

Answer 1

ForEach(materials.indices)
Needs to be
ForEach(materials.indices, id: \.self)
Because you are not using a compile-time constant in ForEach.
In general for fixed selections like this your code can be much simpler if you make everything enums, and make the enums Identifiable. This simplified example only shows one set of materials but you could return an array of applicable materials depending on the selected series (which could also be an enum?)
enum Material: Identifiable, CaseIterable {
case hp, lf, steel
var id: Material { self }
var title: String {
... return an appropriate title
}
}
#State var material: Material
...
Picker("Material", selection: $material) {
ForEach(Material.allCases) {
Text($0.title)
}
}