onChange(of:) not working for childState

[Eunno-An]

Hello?
I have a question..

This is a parent Feature code.
It use child feature 'ProfileHeaderFeature'
But, the BindingReducer Never called.
Why it happened?

*profileHeaderFeature inside, there is BindingReducer.
*So i tested another child feature not have BindingReducer.

@Reducer
struct ProfileFeature {
    @ObservableState
    struct State {
        var profileHeaderFeature: ProfileHeaderFeature.State?
        ...
        
        init(profileHeaderFeature: ProfileHeaderFeature.State, introFeature: IntroFeature.State, hashTagComponentFeatures: IdentifiedArrayOf<HashTagComponentFeature.State>, saveFeature: SaveFeature.State) {
            self.profileHeaderFeature = profileHeaderFeature
            ...
        }
    }
    enum Action: BindableAction {
        case binding(BindingAction<State>)
        case profileHeaderFeature(ProfileHeaderFeature.Action)
        ...
    }
    var body: some ReducerOf<Self> {
        BindingReducer()
            .onChange(of: \.introFeature) { oldValue, newValue in
                self._printChanges()
            }
        Scope(state: \.profileHeaderFeature!, action: \.profileHeaderFeature) {
            ProfileHeaderFeature()
        }
...
}

[stephencelis]

@Eunno-An We might need more info or a project to work with, but note that onChange only detects changes made by the reducer it's attached to, which means it'll only detect changes to \.introFeature by the BindingReducer installed in ProfileFeature. Also, note that re-embedding self._printChanges() inside the onChange is probably not what you want, as that will recursively re-run self again, which could lead to an infinite loop. If you want to simply debug in here, you could call let _ = print("introFeature", oldValue, newValue).

To detect changes made by all reducers in the body, you must wrap everything with CombineReducers and apply onChange to that:

 var body: some ReducerOf<Self> {
+  CombineReducers {
     BindingReducer()
-      .onChange(of: \.introFeature) { oldValue, newValue in
-        self._printChanges()
-      }
     Scope(state: \.profileHeaderFeature!, action: \.profileHeaderFeature) {
       ProfileHeaderFeature()
     }
     ...
+  }
+  .onChange(of: \.introFeature) { oldValue, newValue in
+    let _ = print("introFeature", oldValue, newValue)
+  }
 }