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I try now since a while to use data from a entity that be selected in a picker. But I feel in the moment like running again a wall and don't see the next step. So I hope I can get a tip from you which push me into the better way.

I have the following two entities, who be related with one-to-many (one manufacturer can have multiple type of devices)

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In the application I list all types in a picker that it can be choosen for the calculation.

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The code for the picker is

Picker("Select Type", selection: $selectedType) { ForEach(0..<types.count, id: \.self) { index in Text("\(types[index].wrappedName)") .tag(index) } }

I can't get the origin indexkey for the row that I select in the picker. Is this the uuid? Also I can't add the manufacturer.name to the text in the picker.

Please give me a tip in which way I have to look.

Thanks a lot.

Here is the fully View

import SwiftUI import CoreData struct CalculateCopyView: View { @Environment(\.managedObjectContext) private var viewContext @FetchRequest( sortDescriptors: [], predicate: NSPredicate(format: "favorite == %@", true as NSNumber), animation: .default) var types: FetchedResults<TypeEntity> @State private var selectedType: Int = 0 @State private var selectedBarString = "Top" let barOptions: [String] = ["Top","Front"] //This Data should be filled from database @State private var winkel: Double = 15 @State private var laengeSchleifstueck: Double = 140 @State private var durchmesserSchleifrad: Double = 250.3 @State private var horizontal: Double = 50 @State private var vertikal: Double = 29 //*********************** let formatter: NumberFormatter = { let formatter = NumberFormatter() formatter.numberStyle = .decimal return formatter }() func calculateBar(h: Double,v: Double) -> Double { let t = h + v return t } //This function should called always when one of the pickers would be //changed and when the view would viewed for the first time with the //first automatically selected value from the type-picker func fetchDataforSelectedType (v: String) { // v = value of the picker for the types (devices) @FetchRequest( sortDescriptors: [], predicate: NSPredicate(format: "name == %@", v), animation: .default ) var types: FetchedResults<TypeEntity> switch selectedBarString { case "top": horizontal = types[0].topHorizontal vertikal = types[0].topVertical case "front": horizontal = types[0].frontHorizontal vertikal = types[0].frontVertical default: print("no kind of bar is choosen") } } var body: some View { Form { Section { VStack { Picker("Select Type", selection: $selectedType) { ForEach(0..<types.count, id: \.self) { type in Text("\(types[type].wrappedName)") .tag(types[type]) } } } } Section { VStack { Picker(selection: $selectedBarString, label: Text("Select Bar")) { ForEach(barOptions.indices, id: \.self) { index in Text(barOptions[index]) .tag(barOptions[index]) } } .pickerStyle(SegmentedPickerStyle()) } } Section { VStack { HStack { Text("Schleifrad") TextField("Enter your score", value: $durchmesserSchleifrad, formatter: formatter) .textFieldStyle(OutlinedTextFieldStyle(icon: Image(systemName: "pencil"))) } } .onTapGesture { hideKeyboard() } VStack { HStack { Text("length tool") TextField("Enter your score", value: $laengeSchleifstueck, formatter: formatter) .textFieldStyle(OutlinedTextFieldStyle(icon: Image(systemName: "pencil"))) } } .onTapGesture { hideKeyboard() } VStack { Text("angle") .frame(maxWidth: .infinity, alignment: .leading) HStack { Slider(value: $winkel , in: 7.0...32.0, step: 1.0) Text( String(format: "%.0f °", winkel) ) } } .onTapGesture { hideKeyboard() } } .padding() Section { VStack { HStack { Text("Topbar: " ) .font(.title) Text(String(format: "%.1f mm", calculateBar(h: horizontal, v: vertikal))) .font(.title) .frame(maxWidth: .infinity, alignment: .trailing) } } .onTapGesture { hideKeyboard() } } } } }
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2 Answers 2

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Alternatively you could let the Picker pick a 'Type' directly. Just define selectedType as type TypeEntity?.

The manufacturer can be accessed directly from the type through the to-one relation: type.manufacturer

struct TypesView: View { @FetchRequest( sortDescriptors: [NSSortDescriptor(keyPath: \TypeEntity.name, ascending: true)], animation: .default) private var types: FetchedResults<TypeEntity> @State private var selectedType: TypeEntity? = nil // directly pick an (optional) TypeEntity var body: some View { Form { Picker("Select Type", selection: $selectedType) { Text("keine Auswahl").tag(nil as TypeEntity?) ForEach(types) { type in Text(type.name ?? "?").tag(type as TypeEntity?) } } if let type = selectedType { let hersteller = type.manufacturer // access manufacturer through type to-one relation Text("Hersteller: \(hersteller?.name ?? "?")") } } .padding() } }
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As selectedType is Int, the tag must be Int, too.

Renaming type as index makes it clearer

Picker("Select Type", selection: $selectedType) { ForEach(0..<types.count, id: \.self) { index in Text(types[index].wrappedName) .tag(index) } }

And – unrelated – string interpolating a string is pointless

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