How to move to next field programmatically in nested custom form with custom fields in SwiftUI – Ios swift

I found my issue, I was using @State to track the current focused field, which is getting reset every time the view changes.

So I had to us @ObservableObject with @Published property.

Here is my final working code.

Custom field

enum InputFieldType {
    case text, number, dropdown
}

struct CustomField: View {
    let tag: Int
    let type: InputFieldType
    let title: String
    var dropdownItems: Array<String> = []
    var placeholder: String = ""
    @State var text: String = ""
    @State var enabled: Bool = true
    @Binding var focusTag: Int

    @FocusState private var focusField: Bool
    private let dropdownImage = Image(systemName: "chevron.down")
    @State private var showDropdown: Bool = false

    var body: some View {
        VStack(alignment: .leading, spacing: 8.0) {
            Text(title)
                .foregroundColor(.gray)
                .frame(alignment: .leading)
            ZStack(alignment: .leading) {
                // The placeholder view
                Text(placeholder).foregroundColor( enabled ? .gray.opacity(0.3) : .gray.opacity(0.5))
                    .opacity(text.isEmpty ? 1 : 0)
                    .padding(.horizontal, 8)
                // Text field
                TextField("", text: $text)
                    .disabled(!enabled)
                    .frame(height: 44)
                    .textInputAutocapitalization(.sentences)
                    .foregroundColor(.white)
                    .padding(.horizontal, 8)
                    .keyboardType( type == .number ? .decimalPad : .default)
                    .onChange(of: focusTag, perform: { newValue in
                        focusField = newValue == tag
                    })
                    .focused($focusField)
                    .onChange(of: focusField, perform: { newValue in
                        if type != .dropdown, newValue, focusTag != tag {
                            focusTag = tag
                        }
                    })

            }.background(Color.red.opacity(0.1))
                .cornerRadius(5)
        }
    }
}

Form view

fileprivate class FocusStateObserver: ObservableObject {
    @Published var focusFieldTag: Int = -1
}

struct FormView: View {

    @ObservedObject private var focusStateObserver = FocusStateObserver()

    func moveToNextField() -> Bool {
        if focusStateObserver.focusFieldTag < 4 {
            switch focusStateObserver.focusFieldTag {
            case 0:
                focusStateObserver.focusFieldTag = 1
            case 1:
                focusStateObserver.focusFieldTag = 2
            case 2:
                focusStateObserver.focusFieldTag = 4
            default:
                break
            }

            return true
        }

        return false
    }

    var body: some View {
        VStack {
            ScrollView(.vertical) {
                VStack(spacing: 24) {
                    CustomField(tag: 0, type: .text, title: "First name", placeholder: "John", text: "", enabled: false, focusTag: $focusStateObserver.focusFieldTag)
                    CustomField(tag: 1, type: .text, title: "Surname", placeholder: "Mike", text: "", focusTag: $focusStateObserver.focusFieldTag)
                    CustomField(tag: 2, type: .text, title: "Gender (Optional)", placeholder: "Optional", text: "", focusTag: $focusStateObserver.focusFieldTag)
                    CustomField(tag: 3, type: .dropdown, title: "Body type", dropdownItems: ["1", "2", "3"], placeholder: "Skinny", text: "", focusTag: $focusStateObserver.focusFieldTag)
                    CustomField(tag: 4, type: .number, title: "Year of birth", placeholder: "2000", text: "", focusTag: $focusStateObserver.focusFieldTag)
                    Spacer()
                }
            }
        }.onTapGesture {
            endEditing()
        }
        .background(Color.clear)
        .padding(.horizontal, 16)
    }
}

extension View {
    func endEditing() {
        UIApplication.shared.sendAction(#selector(UIResponder.resignFirstResponder), to: nil, from: nil, for: nil)
    }
}

Content view

struct ContentView: View {

    let formView = FormView()
    var body: some View {
        VStack {
            Spacer(minLength: 30)
            formView
                .padding(.vertical)
            Button("Next") {
                if formView.moveToNextField()  {
                    return
                }
                endEditing()
            }.frame(minWidth: 0, maxWidth: .infinity, minHeight: 44, maxHeight: 44, alignment: .center)
                .background(Color.secondary)
                .cornerRadius(5)
                .padding(.horizontal, 16)
            Spacer(minLength: 20)
        }.background(Color.primary)
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView().preferredColorScheme(.dark)
    }
}