@focusstate case study. (#690)

* @focusstate case study.

* compiler version

Author: mbrandonw

Examples/CaseStudies/CaseStudies.xcodeproj/project.pbxproj

@@ -13,6 +13,7 @@
 		CA25E5D224463AD700DA666A /* 01-GettingStarted-Bindings-Basics.swift in Sources */ = {isa = PBXBuildFile; fileRef = CA25E5D124463AD700DA666A /* 01-GettingStarted-Bindings-Basics.swift */; };
 		CA27C0B7245780CE00CB1E59 /* 03-Effects-SystemEnvironment.swift in Sources */ = {isa = PBXBuildFile; fileRef = CA27C0B6245780CE00CB1E59 /* 03-Effects-SystemEnvironment.swift */; };
 		CA34170824A4E89500FAF950 /* 01-GettingStarted-AnimationsTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = CA34170724A4E89500FAF950 /* 01-GettingStarted-AnimationsTests.swift */; };
+		CA3E421F26B8337500581ABC /* 01-GettingStarted-FocusState.swift in Sources */ = {isa = PBXBuildFile; fileRef = CA3E421E26B8337500581ABC /* 01-GettingStarted-FocusState.swift */; };
 		CA3E4C5B24B4FA0E00447C0B /* 04-HigherOrderReducers-Lifecycle.swift in Sources */ = {isa = PBXBuildFile; fileRef = CA3E4C5A24B4FA0E00447C0B /* 04-HigherOrderReducers-Lifecycle.swift */; };
 		CA410EE0247A15FE00E41798 /* 02-Effects-WebSocket.swift in Sources */ = {isa = PBXBuildFile; fileRef = CA410EDF247A15FE00E41798 /* 02-Effects-WebSocket.swift */; };
 		CA410EE2247C73B400E41798 /* 02-Effects-WebSocketTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = CA410EE1247C73B400E41798 /* 02-Effects-WebSocketTests.swift */; };
@@ -156,6 +157,7 @@
 		CA25E5D124463AD700DA666A /* 01-GettingStarted-Bindings-Basics.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "01-GettingStarted-Bindings-Basics.swift"; sourceTree = "<group>"; };
 		CA27C0B6245780CE00CB1E59 /* 03-Effects-SystemEnvironment.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "03-Effects-SystemEnvironment.swift"; sourceTree = "<group>"; };
 		CA34170724A4E89500FAF950 /* 01-GettingStarted-AnimationsTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "01-GettingStarted-AnimationsTests.swift"; sourceTree = "<group>"; };
+		CA3E421E26B8337500581ABC /* 01-GettingStarted-FocusState.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "01-GettingStarted-FocusState.swift"; sourceTree = "<group>"; };
 		CA3E4C5A24B4FA0E00447C0B /* 04-HigherOrderReducers-Lifecycle.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "04-HigherOrderReducers-Lifecycle.swift"; sourceTree = "<group>"; };
 		CA410EDF247A15FE00E41798 /* 02-Effects-WebSocket.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "02-Effects-WebSocket.swift"; sourceTree = "<group>"; };
 		CA410EE1247C73B400E41798 /* 02-Effects-WebSocketTests.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "02-Effects-WebSocketTests.swift"; sourceTree = "<group>"; };
@@ -399,6 +401,7 @@
 				DC5B505025C86EBC000D8DFD /* 01-GettingStarted-Bindings-Forms.swift */,
 				DCC68EE02447C4630037F998 /* 01-GettingStarted-Composition-TwoCounters.swift */,
 				DC89C4432446111B006900B9 /* 01-GettingStarted-Counter.swift */,
+				CA3E421E26B8337500581ABC /* 01-GettingStarted-FocusState.swift */,
 				DCC68EDC2447A5B00037F998 /* 01-GettingStarted-OptionalState.swift */,
 				CA7BC8ED245CCFE4001FB69F /* 01-GettingStarted-SharedState.swift */,
 				CAA9ADC12446587C0003A984 /* 02-Effects-Basics.swift */,
@@ -744,6 +747,7 @@
 				DC89C45324465452006900B9 /* 03-Navigation-Lists-NavigateAndLoad.swift in Sources */,
 				CAF069D024ACC5AF00A1AAEF /* 00-Core.swift in Sources */,
 				DCC68EE32447C8540037F998 /* 04-HigherOrderReducers-ReusableFavoriting.swift in Sources */,
+				CA3E421F26B8337500581ABC /* 01-GettingStarted-FocusState.swift in Sources */,
 				DCC68EDF2447BC810037F998 /* TemplateText.swift in Sources */,
 				DCAC2A4F2452352E0094DEF5 /* 04-HigherOrderReducers-ElmLikeSubscriptions.swift in Sources */,
 				CA6AC2672451135C00C71CB3 /* DownloadClient.swift in Sources */,

Examples/CaseStudies/SwiftUICaseStudies/00-Core.swift

@@ -15,6 +15,7 @@ struct RootState {
   var effectsCancellation = EffectsCancellationState()
   var effectsTimers = TimersState()
   var episodes = EpisodesState(episodes: .mocks)
+  var focusDemo = FocusDemoState()
   var lifecycle = LifecycleDemoState()
   var loadThenNavigate = LoadThenNavigateState()
   var loadThenNavigateList = LoadThenNavigateListState()
@@ -45,6 +46,7 @@ enum RootAction {
   case effectsBasics(EffectsBasicsAction)
   case effectsCancellation(EffectsCancellationAction)
   case episodes(EpisodesAction)
+  case focusDemo(FocusDemoAction)
   case lifecycle(LifecycleDemoAction)
   case loadThenNavigate(LoadThenNavigateAction)
   case loadThenNavigateList(LoadThenNavigateListAction)
@@ -160,6 +162,12 @@ let rootReducer = Reducer<RootState, RootAction, RootEnvironment>.combine(
       action: /RootAction.episodes,
       environment: { .init(favorite: $0.favorite, mainQueue: $0.mainQueue) }
     ),
+  focusDemoReducer
+    .pullback(
+      state: \.focusDemo,
+      action: /RootAction.focusDemo,
+      environment: { _ in .init() }
+    ),
   lifecycleDemoReducer
     .pullback(
       state: \.lifecycle,

Examples/CaseStudies/SwiftUICaseStudies/00-RootView.swift

@@ -81,6 +81,18 @@ struct RootView: View {
               )
             )
 
+            #if compiler(>=5.5)
+            NavigationLink(
+              "Focus State",
+              destination: FocusDemoView(
+                store: self.store.scope(
+                  state: \.focusDemo,
+                  action: RootAction.focusDemo
+                )
+              )
+            )
+            #endif
+
             NavigationLink(
               "Animations",
               destination: AnimationsView(

Examples/CaseStudies/SwiftUICaseStudies/01-GettingStarted-FocusState.swift

@@ -0,0 +1,110 @@
+import ComposableArchitecture
+import SwiftUI
+
+private let readMe = """
+  This demonstrates how to make use of SwiftUI's `@FocusState` in the Composable Architecture. \
+  If you tap the "Sign in" button while a field is empty, the focus will be changed to that field.
+  """
+
+struct FocusDemoState: Equatable {
+  var focusedField: Field? = nil
+  var password: String = ""
+  var username: String = ""
+
+  enum Field: String, Hashable {
+    case username, password
+  }
+}
+
+enum FocusDemoAction: Equatable {
+  case binding(BindingAction<FocusDemoState>)
+  case signInButtonTapped
+}
+
+struct FocusDemoEnvironment {}
+
+let focusDemoReducer = Reducer<
+  FocusDemoState,
+  FocusDemoAction,
+  FocusDemoEnvironment
+> { state, action, _ in
+  switch action {
+  case .binding:
+    return .none
+
+  case .signInButtonTapped:
+    if state.username.isEmpty {
+      state.focusedField = .username
+    } else if state.password.isEmpty {
+      state.focusedField = .password
+    }
+    return .none
+  }
+}
+.binding(action: /FocusDemoAction.binding)
+
+#if compiler(>=5.5)
+struct FocusDemoView: View {
+  let store: Store<FocusDemoState, FocusDemoAction>
+  @FocusState var focusedField: FocusDemoState.Field?
+
+  var body: some View {
+    WithViewStore(self.store) { viewStore in
+      VStack(alignment: .leading, spacing: 32) {
+        Text(template: readMe, .caption)
+
+        VStack {
+          TextField(
+            "Username",
+            text: viewStore.binding(keyPath: \.username, send: FocusDemoAction.binding)
+          )
+            .focused($focusedField, equals: .username)
+
+          SecureField(
+            "Password",
+            text: viewStore.binding(keyPath: \.password, send: FocusDemoAction.binding)
+          )
+            .focused($focusedField, equals: .password)
+
+          Button("Sign In") {
+            viewStore.send(.signInButtonTapped)
+          }
+        }
+
+        Spacer()
+      }
+      .padding()
+      .synchronize(
+        viewStore.binding(keyPath: \.focusedField, send: FocusDemoAction.binding),
+        self.$focusedField
+      )
+    }
+    .navigationBarTitle("Focus demo")
+  }
+}
+
+extension View {
+  func synchronize<Value: Equatable>(
+    _ first: Binding<Value>,
+    _ second: FocusState<Value>.Binding
+  ) -> some View {
+    self
+      .onChange(of: first.wrappedValue) { second.wrappedValue = $0 }
+      .onChange(of: second.wrappedValue) { first.wrappedValue = $0 }
+  }
+}
+
+struct FocusDemo_Previews: PreviewProvider {
+  static var previews: some View {
+    NavigationView {
+      FocusDemoView(
+        store: Store(
+          initialState: .init(),
+          reducer: focusDemoReducer,
+          environment: .init()
+        )
+      )
+    }
+  }
+}
+#endif