TextField binding not updating on iOS17

[marioradonic]

Description

In the case where BindingState is updated directly in the action that updated it the TextField value is not updated.
Tested with SCA 1.6.0 on iOS17 where it happens, and iOS16 where it doesn't happen.

Minimal reproducible example:

import SwiftUI
import ComposableArchitecture

@main
struct TestBindingApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView().task {
                runTest()
            }
        }
    }
}

@Reducer
struct SomeReducer {
    struct State: Equatable {
        @BindingState var text = ""
    }
    enum Action: BindableAction {
        case binding(BindingAction<State>)
    }

    var body: some ReducerOf<Self> {
        BindingReducer()
        Reduce { state, action in
            switch action {
            case .binding(\.$text):
                if state.text == "123" {
                    state.text = ""
                }
            case .binding:
                break
            }
            return .none
        }
    }
}

struct ViewState: Equatable {
    @BindingViewState var text: String

    init(state: BindingViewStore<SomeReducer.State>) {
        self._text = state.$text
    }
}

struct ContentView: View {
    let store = Store(initialState: .init()) {
        SomeReducer()._printChanges()
    }

    var body: some View {
        WithViewStore(store, observe: ViewState.init) { viewStore in
            VStack {
                Text(viewStore.text)
                TextField("Title", text: viewStore.$text).textFieldStyle(.plain)
            }
        }
    }
}

Checklist

• I have determined whether this bug is also reproducible in a vanilla SwiftUI project.
• If possible, I've reproduced the issue using the main branch of this package.
• This issue hasn't been addressed in an existing GitHub issue or discussion.

Expected behavior

In the above example I would expect both Text and TextField values to reset to empty string if I type in "123".

Actual behavior

The value of the Text updates, but the value of the TextField stays "123".

Screen.Recording.2024-01-19.at.10.43.17.mov

Steps to reproduce

No response

The Composable Architecture version information

1.6.0

Destination operating system

iOS 17

Xcode version information

15.2

Swift Compiler version information

swift-driver version: 1.87.3 Apple Swift version 5.9.2 (swiftlang-5.9.2.2.56 clang-1500.1.0.2.5)
Target: arm64-apple-macosx13.0

[stephencelis]

@marioradonic How did you rule out this behavior in vanilla SwiftUI? If I use a vanilla observable object instead of a store I can reproduce the exact same behavior:

class Model: ObservableObject {
  @Published var text = "" {
    didSet {
      if text == "123" {
        text = ""
      }
    }
  }
}

struct ContentView: View {
  @ObservedObject var model = Model()
  
  var body: some View {
    VStack {
      Text(model.text)
      TextField("Title", text: $model.text).textFieldStyle(.plain)
    }
  }
}

Because this appears to be a vanilla SwiftUI behavior and not a bug in TCA, I'm going to convert to a discussion, where workarounds may be discussed.

[marioradonic]

Ah what a gnarly bug, my bad... I've used @State var and observed it onChange.
Do you think this bug could use a warning in the BindingState documentation?

[arkulpaKonstantin]

I have stumbled upon this issue today and for me the easiest fix was to add a new action which handles the validation of the input. In the binding action for the input I then used the .run effect to send that action back into the system. One has to use the .run effect and not the .send effect for it to work, I guess the .run effect does a thread hop that the .send effect does not.

This is clearly not ideal as the UI shows the entered character for a brief moment, but for our use case it was sufficient and easier then doing anything with @State and any kind of synchronization logic (which I not even got working correctly when I tried).