AlertState

public struct AlertState<Action>

extension AlertState: Equatable where Action: Equatable

extension AlertState: Hashable where Action: Hashable

extension AlertState: Identifiable where Action: Hashable

A data type that describes the state of an alert that can be shown to the user. The Action generic is the type of actions that can be sent from tapping on a button in the alert.

This type can be used in your application’s state in order to control the presentation or dismissal of alerts. It is preferrable to use this API instead of the default SwiftUI API for alerts because SwiftUI uses 2-way bindings in order to control the showing and dismissal of alerts, and that does not play nicely with the Composable Architecture. The library requires that all state mutations happen by sending an action so that a reducer can handle that logic, which greatly simplifies how data flows through your application, and gives you instant testability on all parts of your application.

To use this API, you model all the alert actions in your domain’s action enum:

enum AppAction: Equatable {
  case cancelTapped
  case confirmTapped
  case deleteTapped

  // Your other actions
}

And you model the state for showing the alert in your domain’s state, and it can start off nil:

struct AppState: Equatable {
  var alert = AlertState<AppAction>?

  // Your other state
}

Then, in the reducer you can construct an AlertState value to represent the alert you want to show to the user:

let appReducer = Reducer<AppState, AppAction, AppEnvironment> { state, action, env in
  switch action
    case .cancelTapped:
      state.alert = nil
      return .none

    case .confirmTapped:
      state.alert = nil
      // Do deletion logic...

    case .deleteTapped:
      state.alert = .init(
        title: "Delete",
        message: "Are you sure you want to delete this? It cannot be undone.",
        primaryButton: .default("Confirm", send: .confirmTapped),
        secondaryButton: .cancel()
      )
    return .none
  }
}

And then, in your view you can use the .alert(_:send:dismiss:) method on View in order to present the alert in a way that works best with the Composable Architecture:

Button("Delete") { viewStore.send(.deleteTapped) }
  .alert(
    self.store.scope(state: \.alert),
    dismiss: .cancelTapped
  )

This makes your reducer in complete control of when the alert is shown or dismissed, and makes it so that any choice made in the alert is automatically fed back into the reducer so that you can handle its logic.

Even better, you can instantly write tests that your alert behavior works as expected:

let store = TestStore(
  initialState: AppState(),
  reducer: appReducer,
  environment: .mock
)

store.assert(
  .send(.deleteTapped) {
    $0.alert = .init(
      title: "Delete",
      message: "Are you sure you want to delete this? It cannot be undone.",
      primaryButton: .default("Confirm", send: .confirmTapped),
      secondaryButton: .cancel(send: .cancelTapped)
    )
  },
  .send(.deleteTapped) {
    $0.alert = nil
    // Also verify that delete logic executed correctly
  }
)