Unexpected TextField Binding Invocations

[nickkohrn]

I'm hoping you can help me understand why I am seeing multiple invocations of a @BindableState var value: Int? whenever the related TextField is focused, defocused, and the containing view is dismissed.

The output that I see follows (some output omitted):

[ProjectFeature] Presenting filter configuration
[FilterConfigurationFeature] Filter changed to hydrogen
[FilterConfigurationFeature] Unit changed to hour
[FilterConfigurationFeature] Value changed to nil ⬅️ TextField-containing view presented
[FilterConfigurationFeature] Value changed to nil ⬅️ TextField-containing view presented
[FilterConfigurationFeature] Value changed to 1 ⬅️ TextField input changed
[FilterConfigurationFeature] Value changed to 1 ⬅️ TextField input changed
[FilterConfigurationFeature] Value changed to 10 ⬅️ TextField input changed
[FilterConfigurationFeature] Value changed to 10 ⬅️ TextField input changed
[FilterConfigurationFeature] Saving filter configuration
[ProjectFeature] Filter configuration: FilterConfiguration(filter: hydrogen, targetDuration: ExposureDuration(value: 10, unit: AstrophotographyTracker.ExposureDurationUnit.hours), id: AFEF1353-1E12-4EE1-BB1D-D4A0EAEF3B00
[ProjectFeature] Saved filter configuration
[ProjectFeature] Dismissing filter configuration
[FilterConfigurationFeature] Value changed to 10 ⬅️ After TextField-containing view dismissed
[FilterConfigurationFeature] Value changed to 10 ⬅️ After TextField-containing view dismissed

The basic structure follows (irrelevant code omitted):

struct FilterConfigurationFeature: ReducerProtocol {
    struct State: Equatable {
        @BindableState var value: Int?
    }

    enum Action: BindableAction, Equatable {
        case binding(BindingAction<State>)
        case cancel
        case save
    }

    var body: some ReducerProtocol<State, Action> {
        BindingReducer()
        Reduce { state, action in
            switch action {
            case .binding(\.$value):
                if let value = state.value {
                    Logger.filterConfigurationFeature.info("Value changed to \(value, privacy: .public)")
                } else {
                    Logger.filterConfigurationFeature.info("Value changed to nil")
                }
                return .none

            case .binding:
                return .none
                
            case .cancel:
                Logger.filterConfigurationFeature.info("Cancelled filter configuration")
                return .none
                
            case .save:
                Logger.filterConfigurationFeature.info("Saving filter configuration")
                return .none
            }
        }
    }
}

struct ProjectFeature: ReducerProtocol {
    struct State: Equatable {
        var filterConfigurationState: FilterConfigurationFeature.State?
        var showFilterConfiguration = false
    }
    
    enum Action: BindableAction, Equatable {
        case binding(BindingAction<State>)
        case dismissFilterConfiguration
        case filterConfiguration(FilterConfigurationFeature.Action)
        case showFilterConfiguration(Bool)
    }
    
    var body: some ReducerProtocol<State, Action> {
        BindingReducer()
        Reduce { state, action in
            switch action {
            case .binding:
                return .none

            case .dismissFilterConfiguration:
                state.showFilterConfiguration = false
                return .none
                
            case .filterConfiguration(.cancel):
                return .run {
                    await $0.send(.dismissFilterConfiguration)
                }
                
            case .filterConfiguration(.save):
                guard let filterConfigurationState = state.filterConfigurationState else {
                    Logger.projectFeature.critical("Expected \(String(describing: FilterConfigurationFeature.State.self))")
                    assertionFailure("Expected \(String(describing: FilterConfigurationFeature.State.self))")
                    return .none
                }
                guard let value = filterConfigurationState.value else {
                    Logger.projectFeature.critical("Expected \(String(describing: FilterConfigurationFeature.State.self)).value")
                    assertionFailure("Expected \(String(describing: FilterConfigurationFeature.State.self)).value")
                    return .none
                }
                let filterConfiguration = FilterConfiguration(
                    filter: filterConfigurationState.filter,
                    targetDuration: .init(
                        value: value,
                        unit: filterConfigurationState.unit
                    )
                )
                Logger.projectFeature.debug("Filter configuration: \(filterConfiguration, privacy: .public)")
                state.filterConfigurations.insert(filterConfiguration, at: 0)
                Logger.projectFeature.info("Saved filter configuration")
                return .run {
                    await $0.send(.dismissFilterConfiguration)
                }
                
            case .filterConfiguration:
                return .none
                
            case .showFilterConfiguration(let show):
                if show {
                    state.filterConfigurationState = .init()
                    Logger.projectFeature.info("Presenting filter configuration")
                } else {
                    Logger.projectFeature.info("Dismissing filter configuration")
                }
                state.showFilterConfiguration = show
                return .none
            }
        }
        .ifLet(\.filterConfigurationState, action: /Action.filterConfiguration) {
            FilterConfigurationFeature()
        }
    }
}

If it's helpful, this branch exhibits the behavior in question.

Is this caused by my ignorance?

[mbrandonw]

Hi @nickkohrn, this is a bug in SwiftUI unfortunately. Here's a few past discussions:

• Double Bindings - iOS 15 #800
• Action send object 2 time in one change #1431

The only work around we know is to add the Binding.removeDuplicates() helper to your project and apply it to the binding returned from viewStore.binding(…).

[nickkohrn]

@mbrandonw Whoa! I searched for related discussions, but I somehow missed those. I appreciate you pointing me to them and providing a solution.

I apologize for not finding the other discussions before submitting mine.

Many thanks!

[yuanhang]

There is another workaround I know. Just append .textFieldStyle(.plain) to TextField() and the problem would go (tested on Xcode 14.2).