Changes on @ObservableObject inside State does not update UI

[raduncicen]

Description

Hello,
I'm building an ARCamera app. It requires me to wrap ARView to a swiftUI wrapper and provide a coordinator class for it which requires me to hold on to a coordinator class inside the ReducerProtocol's State. However the changes I impose on this ObservableObject do not trigger any update on the UI no matter what i do.

Do you guys have a solution for such cases where we need to use a manager observable class inside the state?
In other words, is there a way to trigger UI updates for the changes in ObservableObject(aka ARViewCoordinator) that is kept inside the state?

You can see the code below.

The ObservableObject that i need to use.

class ARViewCoordinator: NSObject, ObservableObject {
    public init(mode: Camera.CameraMode, layerGroup: LayerGroup) {
        self.mode = mode
        self.layerGroup = layerGroup
    }
    
    var parent: ARViewContainer?
    @Published var mode: Camera.CameraMode // Enum
    @Published var layerGroup: LayerGroup // This is a struct 
    
    func setParent(as parent: ARViewContainer) {
        self.parent = parent
    }
    
    func addLayer(_ layer: ClassicLayer) {
        layerGroup.layers.insert(layer, at: 0)
    }
}

extension ARViewCoordinator: ARSessionDelegate {
    func session(_ session: ARSession, didAdd anchors: [ARAnchor]) {
        //Some logic in here for adding anchors to ARView.
    }
}

The reducer which i use it

public struct Camera: ReducerProtocol {
    public init() {}
    
    public struct State: Equatable {
        @BindableState var arViewCoordinator: ARViewCoordinator
        var testBool: Bool = false // I'm toggling this so that the updates in arViewCoordinator appear in the screen
    }
    
    public enum Action: BindableAction {
        case binding(BindingAction<State>)
        case addNewLayer
    }
    
    public var body: some ReducerProtocol<State, Action> {
        BindingReducer()
        
        Reduce { state, action in
            switch action {
            case .binding(_):
                return .none
            case .addNewLayer:
                let newLayer = ClassicLayer(cameraMode: .classic,
                                            sublayers: .init(subLayers: ["Zoom", "Zoom", "Zoom"], selectedIndex: 0),
                                            opacity: 1,
                                            isHidden: false,
                                            transformation: .identity)
                state.arViewCoordinator.addLayer(newLayer)
//                state.testBool.toggle()
                return .none
            }
        }
    }
}

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

No response

Actual behavior

No response

Steps to reproduce

No response

The Composable Architecture version information

No response

Destination operating system

IOS 16

Xcode version information

14.0.1

Swift Compiler version information

No response

[tgrapperon]

Hey @raduncicen!
If you're using UIViewRepresentable, its Coordinator is not required to be an ObservableObject, and it will furthermore not be observed as such by the Representable. When using UIViewRepresentable, the Coordinator is private, and usually an implementation detail with which you don't talk directly (for example from a reducer).
I never tried to install the Coordinator as an ObservedObject directly in the UIViewRepresentable, so I don't know if it would work.
So the idea is to wrap UIKit in UIViewRepresentable, ideally with a value-type API and closures/bindings to control it. But in your case, it could maybe work if you simply rewrite your View's init like this:

let store: StoreOf<Camera>
@ObservedObject var viewStore: ViewStoreOf<Camera>
@ObservedObject var coordinator: ARViewCoordinator
init(store: StoreOf<Camera>) {
  self.store = store
  let viewStore = ViewStore(store, observe: { $0 })
  self.viewStore = viewStore
  self.coordinator = viewStore.arViewCoordinator
}

This is probably not how I would do it, but it can be enough to make it work in you case.

This is likely not a TCA bug, as there is nothing that changes in your case to warrant a new view rendering, so I would say that it's working as expected in this situation.

[saroar]

I am also thinking about how to use same login when webView loading to show is page didFinishLoading

[mbrandonw]

Hi @raduncicen, as @tgrapperon points out this is not a bug in TCA and so I'm going to convert this to a discussion.

In general, if you hold reference types in State (such as you are doing with ARViewCoordinator), then changes to those references types do not cause SwiftUI to update its view. This is true of vanilla SwiftUI too.