SwiftUI Focus 2-way Binding

FocusTracking.swift

protocol FocusTracking<FocusField>: AnyObject {
    associatedtype FocusField: Hashable

    var focusedField: FocusField? { get set }
}

struct FocusTrackingView<Content, Target: FocusTracking>: View where Content: View, Target.FocusField: Hashable {
    @FocusState.Binding var focusedField: Target.FocusField?
    let content: Content
    let boundTo: Target
    let defaultValue: Target.FocusField?
    let defaultValueDelay: Double?

    @inlinable public init(
        focusedFieldBinding: FocusState<Target.FocusField?>.Binding,
        boundTo: Target,
        defaultValue: Target.FocusField? = nil,
        defaultValueDelay: Double? = nil,
        @ViewBuilder content: () -> Content
    ) {
        _focusedField = focusedFieldBinding
        self.boundTo = boundTo
        self.defaultValue = defaultValue
        self.defaultValueDelay = defaultValueDelay
        self.content = content()
    }

    var body: some View {
        content
            .onAppear {
                guard let defaultValue = defaultValue else { return }

                let setDefault = {
                    focusedField = defaultValue
                }

                // Delay is needed otherwise the focus won't actually be applied
                if let delay = defaultValueDelay {
                    DispatchQueue.main.asyncAfter(deadline: .now() + delay, execute: setDefault)
                } else {
                    setDefault()
                }
            }
            .onChange(of: boundTo.focusedField) { newValue in
                focusedField = newValue
            }
            .onChange(of: focusedField) { newValue in
                boundTo.focusedField = newValue
            }
    }
}

extension View {
    func bindFocus<T: FocusTracking>(
        from: FocusState<T.FocusField?>.Binding,
        to: T, defaultFocus: T.FocusField? = nil, // swiftlint:disable:this identifier_name
        defaultValueDelay: Double? = nil
    ) -> some View {
        FocusTrackingView(focusedFieldBinding: from, boundTo: to, defaultValue: defaultFocus, defaultValueDelay: defaultValueDelay) {
            self
        }
    }
}