Migrating to 1.13

The Composable Architecture now provides first class tools for building features in UIKit, including minimal state observation, presentation and stack navigation.

Overview

The Composable Architecture is now integrated with the Swift Navigation library, which brings powerful navigation and observation tools to UIKit. You can model your domains as concisely as possible, just as you would in SwiftUI, but then implement your view in UIKit without losing any power.

The simplest tool to use is observe, which allows you to minimally observe changes to state in your feature and update the UI. Typically the best place to do this is in viewDidLoad:

let store: StoreOf<Feature>

func viewDidLoad() {
  super.viewDidLoad()

  // ...

  observe { [weak self] in
    countLabel.text = "Count: \(store.count)"
  }
}

Only the state accessed in the observe trailing closure will be observed. If any other state changes, the closure will not be invoked and no extra work will be performed.

The library also provides powerful navigation tools for UIKit. For example, suppose you have a feature that can present a child feature (see the docs on tree-based navigation for more information on these tools):

@Reducer 
struct Feature {
  @ObservableState
  struct State {
    @Presents var child: ChildFeature.State?
    // ...
  }
  // ...
}

Then you can present a view controller when the child state flips to a non-nil value by using the present(item:) API that comes with the library:

@UIBindable var store: StoreOf<Feature>

func viewDidLoad() {
  super.viewDidLoad()

  present(item: $store.scope(state: \.child, action: \.child)) { store in
    ChildViewController(store: store)
  }
}

Further, if your feature has a stack of features that can be presented, then you can model your domain like so (see the docs on stack-based for more information on these tools):

@Reducer
struct AppFeature {
  struct State {
    var path = StackState<Path.State>()
    // ...
  }

  @Reducer
  enum Path {
    case addItem(AddFeature)
    case detailItem(DetailFeature)
    case editItem(EditFeature)
  }

  // ...
}

And for the view you can subclass NavigationStackController in order to drive navigation from the stack state:

class AppController: NavigationStackController {
  private var store: StoreOf<AppFeature>!

  convenience init(store: StoreOf<AppFeature>) {
    @UIBindable var store = store

    self.init(path: $store.scope(state: \.path, action: \.path)) {
      RootViewController(store: store)
    } destination: { store in 
      switch store.case {
      case .addItem(let store):
        AddViewController(store: store)
      case .detailItem(let store):
        DetailViewController(store: store)
      case .editItem(let store):
        EditViewController(store: store)
      }
    }

    self.store = store
  }
}