UIKit NavigateAndLoad does not work

[havilog]

I'm using TCA with UIKit.

my child reducer doesn't receive any action from view.

so i've tried it with official UIKitCaseStudies - NavigateAndLoad (EagerNavigation Reducer) on main branch,

and it still doesn't work.

is it TCA bug?

[tgrapperon]

There likely was an omission when converting this study to the Reducer protocol. I've submitted a PR to fix this in #1807. It consists in making sure that you embed your child reducer into the parent, here with an ifLet reducer modifier.
I'm not sure this is what's happening in your case, but forgetting to embed a child into a parent (with ifLet, forEach, Scope, …) is usually the principal reason for unresponsive or "dead" child features.

[havilog]

@tgrapperon

Unfortunately, it wasn't my case.
in my case, I made my parent reducer as follows.

    public var body: some ReducerProtocol<State, Action> {
        Reduce(reduce)
            .ifLet(\.optionalChild, action: /Action.optionalChild) { 
                Child()
            }
    }
    
    public func reduce(into state: inout State, action: Action) -> EffectTask<Action> {
        switch action {
        case .something:
            state.optionalChild = .init()
            return .none
        }
    }

my child reducer has not received any action, only the parent reducer received this action.

so I tried like this.

    public var body: some ReducerProtocol<State, Action> {
        Reduce { state, action in
            switch action {
            case .something:
                state.optionalChild = .init()
                return .none
            }
        }
        .ifLet(\.optionalChild, action: /Action.optionalChild) { 
            Child()
        }
    }

and it works.

what is the differance between Reduce(reduce) + ifLet and Reduce { ... } + ifLet ?

[tgrapperon]

The problem in you case was that you defined both body and reduce, and this is something that is not supported. You have to pick one of the styles, otherwise only reduce will be executed.
The thing you tried last is the way you should do. If you want to keep the "core" reducer's implementation out of body, (in the same style you used when it wasn't working), it could also work if you rename the reduce function differently. For example if your rename it core or something like this:

public func core(into state: inout State, action: Action) -> EffectTask<Action> { … }
public var body: some ReducerProtocol<State, Action> {
  Reduce(core)
    .ifLet(\.optionalChild, action: /Action.optionalChild) { 
      Child()
    }
  }

This approach is often used if you have many domains with many ifLet, forEach or Scope, to make the structure more visible to you. It doesn't change the way it works compared to body alone, provided you don't name it reduce!

So to sum up, you can use body, or you can use reduce. In the latter case, if you also implement a body, body will not be executed (which is what was happening). If you want more insight, the thing that is running body is the default implementation of reduce in ReducerProtocol, if you define a reduce function, you override this default implementation, and body is not used.

I wonder if one wouldn't be able to install safeguards about this easy mistake. Xcode doesn't help neither, because it autocompletes very easily the reduce function.

[havilog]

thanks bro. I totally understand :)