App crashes when SwiftUI view with Picker disappears (since iOS 16)

Question

We have an application with some 'chat' functionality where questions are asked and the user can answer with some predefined options: for every question a new view is presented. One of those options is a view with a Picker, since iOS 16 this Picker causes the app to crash when the view with the Picker disappears with following error: Thread 1: Fatal error: Index out of range positioned at class AppDelegate: UIResponder, UIApplicationDelegate { . In the log I can see this error: Swift/ContiguousArrayBuffer.swift:600: Fatal error: Index out of range .

To troubleshoot this issue I refactored the code to a bare minimum where the picker isn't even used but still cause the error to occur. When I remove the Picker from this view it works again.

View where error occurs

struct PickerQuestion: View {
    
    @EnvironmentObject() var questionVM: QuestionVM

    let question: Question
    
    var colors = ["A", "B", "C", "D"]
    @State private var selected = "A"

    var body: some View {
        VStack {
            // When removing the Picker from this view the error does not occur anymore
            Picker("Please choose a value", selection: $selected) {
                ForEach(colors, id: \.self) {
                    Text($0)
                }
            }.pickerStyle(.wheel) // with .menu style the crash does not occur

            Text("You selected: \(selected)")

            Button("Submit", action: {
                // In this function I provide an answer that is always valid so I do not
                // have to use the Picker it's value
                questionVM.answerQuestion(...)

                // In this function I submit the answer to the backend.
                // The backend will provide a new question which can be again a Picker
                // question or another type of question: in both cases the app crashes
                // when this view disappears. (the result of the backend is provided to
                // the view with `DispatchQueue.main.async {}`)
                questionVM.submitAnswerForQuestionWith(questionId: question.id)
            })
        }
    }
}

Parent view where the view above is used (Note: even with all the animation related lines removed the crash still occurs):

struct QuestionContainerView: View {
    
    @EnvironmentObject() var questionVM: QuestionVM
    
    @State var questionVisible = true
    @State var questionId = ""
    
    @State var animate: Bool = false
    
    var body: some View {
        VStack {
            HeaderView(...)
            Spacer()
            if questionVM.currentQuestion != nil {
                ZStack(alignment: .bottom) {
                    if questionVisible {
                        getViewForQuestion(question: questionVM.currentQuestion!)
                            .transition(.asymmetric(
                                insertion: .move(edge: self.questionVM.scrollDirection == .Next ? .trailing : .leading),
                                removal: .opacity
                            ))
                            .zIndex(0)
                            .onAppear {
                                self.animate.toggle()
                            }
                            .environmentObject(questionVM)
                    } else {
                        EmptyView()
                    }
                }
            }
        }
        .onAppear {
            self.questionVM.getQuestion()
        }
        .onReceive(self.questionVM.$currentQuestion) { q in
            if let question = q, question.id != self.questionId {
                self.questionVisible = false
                DispatchQueue.main.asyncAfter(deadline: .now() + 0.4) {
                    withAnimation {
                        self.questionVisible = true
                        self.questionId = question.id
                    }
                }
            }
        }
    }
    
    func getViewForQuestion(question: Question) -> AnyView {
        switch question.questionType {
        case .Picker:
            return AnyView(TestPickerQuestion(question: question))
        case .Other:
            ...
        case ...
        }
    }
}

The app was made originally for iOS 13 but is still maintained: with every new version of iOS the app kept working as expected until now with iOS 16.

Minimal reproducible code: (put TestView in your ContentView )

struct MinimalQuestion {
    var id: String = randomString(length: 10)
    var text: String
    var type: QuestionType
    var answer: String? = nil
    
    enum QuestionType: String {
        case Picker = "PICKER"
        case Info = "INFO"
        case Boolean = "BOOLEAN"
    }
    
    // https://stackoverflow.com/a/26845710/7142073
    private static func randomString(length: Int) -> String {
        let letters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
        return String((0..<length).map{ _ in letters.randomElement()! })
    }
}

class QuestionViewModel: ObservableObject {
    
    @Published var questions: [MinimalQuestion] = []
    
    @Published var current: MinimalQuestion? = nil//MinimalQuestion(text: "Picker Question", type: .Picker)
    
    @Published var scrollDirection: ScrollDirection = .Next
    
    func getQuestion() {
        DispatchQueue.global(qos: .userInitiated).async {
            DispatchQueue.main.asyncAfter(deadline: .now() + Double.random(in: 0.1...0.2)) {
                var question: MinimalQuestion
                switch Int.random(in: 0...2) {
                case 1:
                    question = MinimalQuestion(text: "Info", type: .Info)
                case 2:
                    question = MinimalQuestion(text: "Boolean question", type: .Boolean)
                default:
                    question = MinimalQuestion(text: "Picker Question", type: .Picker)
                }
                self.questions.append(question)
                self.current = question
            }
        }
    }
    
    func answerQuestion(question: MinimalQuestion, answer: String) {
        if let index = self.questions.firstIndex(where: { $0.id == question.id }) {
            self.questions[index].answer = answer
            self.current = self.questions[index]
        }
    }
    
    func submitQuestion(questionId: MinimalQuestion) {
        DispatchQueue.global(qos: .userInitiated).async {
            DispatchQueue.main.asyncAfter(deadline: .now() + Double.random(in: 0.1...0.2)) {
                self.getQuestion()
            }
        }
    }
    
    func restart() {
        self.questions = []
        self.current = nil
        self.getQuestion()
    }
}

struct TestView: View {
    
    @StateObject var questionVM: QuestionViewModel = QuestionViewModel()

    @State var questionVisible = true
    @State var questionId = ""
    
    @State var animate: Bool = false
    
    var body: some View {
        return VStack {
            Text("Questionaire")
            Spacer()
            if questionVM.current != nil {
                ZStack(alignment: .bottom) {
                    if questionVisible {
                        getViewForQuestion(question: questionVM.current!).environmentObject(questionVM)
                            .frame(maxWidth: .infinity)
                            .transition(.asymmetric(
                                insertion: .move(edge: self.questionVM.scrollDirection == .Next ? .trailing : .leading),
                                removal: .opacity
                            ))
                            .zIndex(0)
                            .onAppear {
                                self.animate.toggle()
                            }
                    } else {
                        EmptyView()
                    }
                }.frame(maxWidth: .infinity)
            }
            Spacer()
        }
        .frame(maxWidth: .infinity)
        .onAppear {
            self.questionVM.getQuestion()
        }
        .onReceive(self.questionVM.$current) { q in
            print("NEW QUESTION OF TYPE \(q?.type)")
            if let question = q, question.id != self.questionId {
                self.questionVisible = false
                DispatchQueue.main.asyncAfter(deadline: .now() + 0.4) {
                    withAnimation {
                        self.questionVisible = true
                        self.questionId = question.id
                    }
                }
            }
        }
    }
    
    func getViewForQuestion(question: MinimalQuestion) -> AnyView {
        switch question.type {
        case .Info:
            return AnyView(InfoQView(question: question))
        case .Picker:
            return AnyView(PickerQView(question: question))
        case .Boolean:
            return AnyView(BoolQView(question: question))
        }
    }
}

struct PickerQView: View {
    
    @EnvironmentObject() var questionVM: QuestionViewModel
    
    var colors = ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J"]
    @State private var selected: String? = nil

    let question: MinimalQuestion
    
    var body: some View {
        VStack {
            // When removing the Picker from this view the error does not occur anymore
            Picker("Please choose a value", selection: $selected) {
                ForEach(colors, id: \.self) {
                    Text("\($0)")
                }
            }.pickerStyle(.wheel)

            Text("You selected: \(selected ?? "")")

            Button("Submit", action: {
                questionVM.submitQuestion(questionId: question)
            })
        }.onChange(of: selected) { value in
            if let safeValue = value {
                questionVM.answerQuestion(question: question, answer: String(safeValue))
            }
        }
    }
}

struct InfoQView: View {
    
    @EnvironmentObject() var questionVM: QuestionViewModel
    
    let question: MinimalQuestion
    
    var body: some View {
        VStack {
            Text(question.text)
            Button("OK", action: {
                questionVM.answerQuestion(question: question, answer: "OK")
                questionVM.submitQuestion(questionId: question)
            })
        }
    }
}

struct BoolQView: View {
    
    @EnvironmentObject() var questionVM: QuestionViewModel
    
    let question: MinimalQuestion
    
    @State var isToggled = false
    
    var body: some View {
        VStack {
            Toggle(question.text, isOn: self.$isToggled)
            Button("OK", action: {
                questionVM.answerQuestion(question: question, answer: "\(isToggled)")
                questionVM.submitQuestion(questionId: question)
            })
        }
    }
}

Answer 1

It seems to be a bug in iOS 16.x while using Picker with "wheel style", I had the same issue in my app and used the following workaround:

extension Picker {
    @ViewBuilder
    func pickerViewModifier() -> some View {
        if #available(iOS 16.0, *) {
            self
        } else {
            self.pickerStyle(.wheel)
        }
    }
 }

 struct SomeView: View {
     var body: some View {
         Picker()
             .pickerViewModifier()
     }
 }

Answer 2

This crash still exists on iOS 16.2. It seems to only occur when you use ForEach within your Picker view. Thus the crash disappears when you manually provide each picker option's Text view in the Picker content instead of using ForEach to create the Text picker options.

Of course, hard-coding the picker options is not a feasible workaround in many cases.

But you can also work around the problem by moving the ForEach -loop that generates the picker options into another view. To achieve this define a helper view:

struct PickerContent<Data>: View where Data : RandomAccessCollection, Data.Element : Hashable {
    let pickerValues: Data
    
    var body: some View {
        ForEach(pickerValues, id: \.self) {
            let text = "\($0)"
            Text(text)
        }
    }
}

Then use PickerContent in your Picker instead of ForEach , eg (based on your example):

Picker("Please choose a value", selection: $selected) {
    PickerContent(pickerValues: colors)
}.pickerStyle(.wheel)

Answer 3

I found the same issue with iOS 16.0 and to get the exact same solution nothing worked and at last I had to used UIKit's wrapper with PickerView() in it. Also it only happens with wheel style I guess default works fine for me. Here's the working code to get the same exact wheel picker in iOS 16.

struct CustomUIPicker: UIViewRepresentable {
    
    @Binding var items: [String]
    @Binding var selectedIndex: Int
    
    func makeCoordinator() -> CustomPickerCoordinator {
        CustomPickerCoordinator(items: $items, selectedIndex: $selectedIndex)
    }
    
    func makeUIView(context: Context) -> UIPickerView {
        let pickerView = UIPickerView()
        pickerView.delegate = context.coordinator
        pickerView.dataSource = context.coordinator
        pickerView.selectRow(selectedIndex, inComponent: 0, animated: true)
        return pickerView
    }

    func updateUIView(_ uiView: UIPickerView, context: Context) {
    }
}

extension CustomUIPicker {
    
    class CustomPickerCoordinator: NSObject, UIPickerViewDelegate, UIPickerViewDataSource {
        
        @Binding private var items: [String]
        @Binding var selectedIndex: Int
        
        init(items: Binding<[String]>, selectedIndex: Binding<Int>) {
            _items = items
            _selectedIndex = selectedIndex
        }
        
        func numberOfComponents(in pickerView: UIPickerView) -> Int {
            1
        }
        
        func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
            items.count
        }
        
        func pickerView( _ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
            return items[row]
        }
        
        func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
            selectedIndex = row
        }
    }
}

Here items is list of data you want to display in your wheel picker and selectedIndex is current selected index of your picker view .