Swiftui-Picker doesn't show selected value

Question

Initial position: making two pickers filled from database where the second depends on the first. I followed this Picker Values from a previous picker - CoreData/SwiftUI example and it works pretty good. Only one problem: the second picker doesn't show the selected value.

    @State var courtSelected = 0
    @State var judgeSelected = 0

HStack{
    Picker(selection: $courtSelected, label: Text("Gericht \(courtSelected)")){
        ForEach(0..<courts.count){ court in
            Text("\(courts[court].name ?? "Unknown")")
        }
    }
}
HStack {
    Picker(selection: $judgeSelected, label: Text("Richter: (\(judgeSelected))")){
        ForEach(Array(courts[courtSelected].courtsJudges! as! Set<Judges>), id: \.self) { judge in
            Text("\(judge.gender ?? "") \(judge.title ?? "") \(judge.name ?? "")")
        }
    }
}

Only differences:

1. the modification from NSSet to array
2. I had to change @Binding var judgeSelected:Int to @State, because otherwise I have to hand over the judge selected as Parameter beginning from App-Struct.

Printing the $judgeSelected inside the label demonstrates, that this var is never changed.

Answer 1

Your selection and presentation are differ by type, so add tag:

Picker(selection: $courtSelected, label: Text("Gericht \(courtSelected)")){
    ForEach(0..<courts.count){ court in
        Text("\(courts[court].name ?? "Unknown")").tag(court)  // << here !!
    }
}

Second picker presents objects, so selection should also be an object, like

@State var judgeSelected: Judges? = nil

Next shows similar case so should be helpful https://stackoverflow.com/a/68815871/12299030

Answer 2

try something like this:

    HStack{
        Picker(selection: $courtSelected, label: Text("Gericht \(courtSelected)")){
            ForEach(0..<courts.count){ court in
                Text("\(courts[court].name ?? "Unknown")")
            }
        }
    }
    HStack {
        Picker(selection: $judgeSelected, label: Text("Richter: (\(judgeSelected))")){
            // -- here
            ForEach(Array(Set(courts[courtSelected].courtsJudges!)), id: \.self) { judge in  
                Text("\(judge.gender ?? "") \(judge.title ?? "") \(judge.name ?? "")")
            }
        }.id(UUID())   // <-- here
    }
}

Note also the second ForEach with Set. PS, do not use forced unwrap, ie. no ! in your code.

EDIT-1: to avoid the error with arrayLiteral, try this:

    HStack {
        Picker(selection: $judgeSelected, label: Text("Richter: (\(judgeSelected))")){
            if let theJudges = courts[courtSelected].courtsJudges {
                ForEach(Array(Set(theJudges)), id: \.self) { judge in
                    Text("\(judge.gender ?? "") \(judge.title ?? "") \(judge.name ?? "")")
                }
            }
        }.id(UUID())
    }

EDIT-2:

here is my test code that allows the second picker to depend on the first picker. I used both the id marker, and tag that must match the selection type.

Since you don't show your struct code for court and judge, I created some example structs for those. You will have to adjust the code to cater for your structs.

Used the id of the Judge struct in the second picker for the tag. However, there are other ways to have a Int tag, for example using array indices, such as:

struct Judge: Identifiable, Hashable {
    var id: Int
    var gender: String?
    var name: String?
    var title: String?
}

struct Court: Identifiable, Hashable {
    var id: Int
    var name: String?
    var courtsJudges: [Judge]?
}

struct ContentView: View {
    @State var courtSelected = 0
    @State var judgeSelected = 0
    
    @State var courts: [Court] = [
        Court(id: 0, name: "one",
              courtsJudges: [
                Judge(id: 0, gender: "Male", name: "name1", title: "title1"),
                Judge(id: 1, gender: "Male", name: "name2", title: "title2"),
                Judge(id: 2, gender: "Male", name: "name3", title: "title3")
              ]),
        Court(id: 1, name: "two",
              courtsJudges: [
                Judge(id: 3, gender: "Female", name: "name7", title: "title7"),
                Judge(id: 4, gender: "Female", name: "name8", title: "title8"),
                Judge(id: 5, gender: "Female", name: "name9", title: "title9")
              ])
    ]

    var body: some View {
        VStack (spacing: 77) {
            HStack{
                Picker(selection: $courtSelected, label: Text("Gericht \(courtSelected)")){
                    ForEach(0..<courts.count) { court in
                        Text("\(courts[court].name ?? "Unknown")").tag(court)
                    }
                }
            }
            HStack {
                Picker(selection: $judgeSelected, label: Text("Richter: (\(judgeSelected))")){
                    if let theJudges = courts[courtSelected].courtsJudges {
                        ForEach(Array(Set(theJudges))) { judge in
                            Text("\(judge.gender ?? "") \(judge.title ?? "") \(judge.name ?? "")")
                                .tag(judge.id)
                        }
                    }
                }.id(UUID())
            }
        }.padding()
    }
}

Alternatively:

 HStack {
     Picker(selection: $judgeSelected, label: Text("Richter: (\(judgeSelected))")){
         if let theJudges = courts[courtSelected].courtsJudges, let arr = Array(Set(theJudges)) {
             ForEach(arr.indices, id: \.self) { index in
                 Text("\(arr[index].gender ?? "") \(arr[index].title ?? "") \(arr[index].name ?? "")")
                     .tag(index)
             }
         }
     }.id(UUID())
 }

Answer 3

First: thanks for all the great help so far.

Bringing it all together til now.

The following code creates a picker, but the selection is not shown. Changing to a radioGroup, you can't select anything.

Here's my edited code

struct ContentView: View {
    @Environment(\.managedObjectContext) private var viewContext
    
    @FetchRequest(
        sortDescriptors: [NSSortDescriptor(keyPath: \Courts.name, ascending: true)],
        animation: .default
    )
    private var courts: FetchedResults<Courts>
    
    @State var courtSelected = 0
    @State var judgeSelected = 0
    
    var body: some View {
        HStack{
            Picker(selection: $courtSelected, label: Text("Gericht")){
                ForEach(0..<courts.count){ court in
                    Text("\(courts[court].name ?? "Unknown")").tag(court)
                }
            }
        }
        HStack {
            Picker(selection: $judgeSelected, label: Text("Richter \(judgeSelected)")){
                ForEach(Array(courts[courtSelected].courtsJudges as! Set<Judges>), id: \.self) { judge in
                    Text("\(judge.gender ?? "") \(judge.title ?? "") \(judge.name ?? "")").tag(judge)
                }
            }.id(UUID())
        }
    }
}

The next code still leads to an error

HStack {
    Picker(selection: $judgeSelected, label: Text("Richter: (\(judgeSelected))")){
        if let theJudges = courts[courtSelected].courtsJudges {
            ForEach(Array(Set(theJudges)), id: \.self) { judge in
                Text("\(judge.gender ?? "") \(judge.title ?? "") \(judge.name ?? "")")
            }
        }
    }.id(UUID())
}

I think, the problem has to be anywhere else, because already at the start the picker doesn't show anything and the radios are grey.

Is it, because picker 2 depends on picker 1 and changes when a value in picker 1 is selected?

It's all for macOS on xcode 13.4.1

Answer 4

I created a complete new project with core data, added two entities (Courts and Judges) with two attributes each (id and name).

Then I only made this view:

import SwiftUI
import CoreData

struct ContentView: View {
    @Environment(\.managedObjectContext) private var viewContext
    
    @FetchRequest(
        sortDescriptors: [NSSortDescriptor(keyPath: \Courts.name, ascending: true)],
        animation: .default
    )
    private var courts: FetchedResults<Courts>
    @FetchRequest(
        sortDescriptors: [NSSortDescriptor(keyPath: \Judges.name, ascending: true)],
        animation: .default
    )
    private var judges: FetchedResults<Judges>
    
    @State var courtSelected = 0
    @State var judgeSelected = 0
    
    var body: some View {
        if(courts.count > 0) {
            HStack{
                Picker(selection: $courtSelected, label: Text("Gericht")){
                    ForEach(0..<courts.count){ court in
                        Text("\(courts[court].name ?? "Unknown")").tag(court)
                    }
                }
            }
            HStack {
                Picker(selection: $judgeSelected, label: Text("Richter \(judgeSelected)")){
                    ForEach(Array(courts[courtSelected].courtsJudges as! Set<Judges>), id: \.self) { judge in
                        Text("\(judge.name ?? "")").tag(judge)
                    }
                }.id(UUID())
            }
            HStack {
                Button("neue Gerichte") {
                    addItem()
                    addJudges()
                }
            }
        }
    }
    
    private func addItem() {
        for id in 0..<3 {
            let newItem = Courts(context: viewContext)
            newItem.id = UUID()
            newItem.name = "Gericht Nr. \(id)"
            
            
            do {
                try viewContext.save()
            } catch {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                let nsError = error as NSError
                fatalError("Unresolved error \(nsError), \(nsError.userInfo)")
            }
        }
        
    }
    
    
    private func addJudges() {
        for cd in 0..<courts.count {
            for jd  in 0..<3 {
                let newJudge = Judges(context: viewContext)
                newJudge.id = UUID()
                newJudge.name = "Richter \(jd) am Gericht \(courts[cd].name)"
                newJudge.judgesCourts = courts[cd]
                
                try? viewContext.save()
            }
        }
    }
    
}

The result: both pickers are shown, first ist ok, second shows the right judges, but they are not "selectable"