The Composable Architecture

Co-authored-by: Stephen Celis <stephen.celis@gmail.com>

Examples/CaseStudies/UIKitCaseStudies/LoadThenNavigate.swift

@@ -0,0 +1,137 @@
+import Combine
+import ComposableArchitecture
+import SwiftUI
+import UIKit
+
+struct LazyNavigationState: Equatable {
+  var optionalCounter: CounterState?
+  var isActivityIndicatorHidden = true
+}
+
+enum LazyNavigationAction: Equatable {
+  case optionalCounter(CounterAction)
+  case setNavigation(isActive: Bool)
+  case setNavigationIsActiveDelayCompleted
+}
+
+struct LazyNavigationEnvironment {
+  var mainQueue: AnySchedulerOf<DispatchQueue>
+}
+
+let lazyNavigationReducer = Reducer<
+  LazyNavigationState, LazyNavigationAction, LazyNavigationEnvironment
+>.combine(
+  Reducer { state, action, environment in
+    switch action {
+    case .setNavigation(isActive: true):
+      state.isActivityIndicatorHidden = false
+      return Effect(value: .setNavigationIsActiveDelayCompleted)
+        .delay(for: 1, scheduler: environment.mainQueue)
+        .eraseToEffect()
+    case .setNavigation(isActive: false):
+      state.optionalCounter = nil
+      return .none
+    case .setNavigationIsActiveDelayCompleted:
+      state.isActivityIndicatorHidden = true
+      state.optionalCounter = CounterState()
+      return .none
+    case .optionalCounter:
+      return .none
+    }
+  },
+  counterReducer.optional.pullback(
+    state: \.optionalCounter,
+    action: /LazyNavigationAction.optionalCounter,
+    environment: { _ in CounterEnvironment() }
+  )
+)
+
+class LazyNavigationViewController: UIViewController {
+  var cancellables: [AnyCancellable] = []
+  let store: Store<LazyNavigationState, LazyNavigationAction>
+  let viewStore: ViewStore<LazyNavigationState, LazyNavigationAction>
+
+  init(store: Store<LazyNavigationState, LazyNavigationAction>) {
+    self.store = store
+    self.viewStore = ViewStore(store)
+    super.init(nibName: nil, bundle: nil)
+  }
+
+  required init?(coder: NSCoder) {
+    fatalError("init(coder:) has not been implemented")
+  }
+
+  override func viewDidLoad() {
+    super.viewDidLoad()
+
+    self.title = "Load then navigate"
+
+    self.view.backgroundColor = .white
+
+    let button = UIButton(type: .system)
+    button.addTarget(self, action: #selector(loadOptionalCounterTapped), for: .touchUpInside)
+    button.setTitle("Load optional counter", for: .normal)
+
+    let activityIndicator = UIActivityIndicatorView()
+    activityIndicator.startAnimating()
+
+    let rootStackView = UIStackView(arrangedSubviews: [
+      button,
+      activityIndicator,
+    ])
+    rootStackView.translatesAutoresizingMaskIntoConstraints = false
+    self.view.addSubview(rootStackView)
+
+    NSLayoutConstraint.activate([
+      rootStackView.centerXAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.centerXAnchor),
+      rootStackView.centerYAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.centerYAnchor),
+    ])
+
+    self.viewStore.publisher.isActivityIndicatorHidden
+      .assign(to: \.isHidden, on: activityIndicator)
+      .store(in: &self.cancellables)
+
+    self.store
+      .scope(state: \.optionalCounter, action: LazyNavigationAction.optionalCounter)
+      .ifLet(
+        then: { [weak self] store in
+          self?.navigationController?.pushViewController(
+            CounterViewController(store: store), animated: true)
+        },
+        else: { [weak self] in
+          guard let self = self else { return }
+          self.navigationController?.popToViewController(self, animated: true)
+        }
+      )
+      .store(in: &self.cancellables)
+  }
+
+  override func viewDidAppear(_ animated: Bool) {
+    super.viewDidAppear(animated)
+
+    if !self.isMovingToParent {
+      self.viewStore.send(.setNavigation(isActive: false))
+    }
+  }
+
+  @objc private func loadOptionalCounterTapped() {
+    self.viewStore.send(.setNavigation(isActive: true))
+  }
+}
+
+struct LazyNavigationViewController_Previews: PreviewProvider {
+  static var previews: some View {
+    let vc = UINavigationController(
+      rootViewController: LazyNavigationViewController(
+        store: Store(
+          initialState: LazyNavigationState(),
+          reducer: lazyNavigationReducer,
+          environment: LazyNavigationEnvironment(
+            mainQueue: DispatchQueue.main.eraseToAnyScheduler()
+          )
+        )
+      )
+    )
+    return UIViewRepresented(makeUIView: { _ in vc.view })
+  }
+}