[SwiftUI Case Studies] Revise initialState and layout in Animations (#1195)

* Remove some unnecessary 'nil' literals in State structs.

* Revise initialState and layout

- move Circle's initial location to center of the screen for better visibility
- align 'circleColor' property's value with actual color using colorInvert()
- remove top margin to display more text because we cannot apply ScrollView in this case

* Update AnimationTests

Author: mluisbrown

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

@@ -38,9 +38,9 @@ extension Effect where Error == Never {
 }
 
 struct AnimationsState: Equatable {
-  var alert: AlertState<AnimationsAction>? = nil
-  var circleCenter = CGPoint(x: 50, y: 50)
-  var circleColor = Color.white
+  var alert: AlertState<AnimationsAction>?
+  var circleCenter = CGPoint(x: UIScreen.main.bounds.width / 2, y: UIScreen.main.bounds.height / 2)
+  var circleColor = Color.black
   var isCircleScaled = false
 }
 
@@ -72,7 +72,7 @@ let animationsReducer = Reducer<AnimationsState, AnimationsAction, AnimationsEnv
 
   case .rainbowButtonTapped:
     return .keyFrames(
-      values: [Color.red, .blue, .green, .orange, .pink, .purple, .yellow, .white]
+      values: [Color.red, .blue, .green, .orange, .pink, .purple, .yellow, .black]
         .map { (output: .setColor($0), duration: 1) },
       scheduler: environment.mainQueue.animation(.linear)
     )
@@ -116,6 +116,7 @@ struct AnimationsView: View {
 
             Circle()
               .fill(viewStore.circleColor)
+              .colorInvert()
               .blendMode(.difference)
               .frame(width: 50, height: 50)
               .scaleEffect(viewStore.isCircleScaled ? 2 : 1)
@@ -149,6 +150,7 @@ struct AnimationsView: View {
         }
         .alert(self.store.scope(state: \.alert), dismiss: .dismissAlert)
       }
+      .navigationBarTitleDisplayMode(.inline)
     }
   }
 }

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

@@ -7,7 +7,7 @@ private let readMe = """
   """
 
 struct FocusDemoState: Equatable {
-  @BindableState var focusedField: Field? = nil
+  @BindableState var focusedField: Field?
   @BindableState var password: String = ""
   @BindableState var username: String = ""
 

Examples/CaseStudies/SwiftUICaseStudiesTests/01-GettingStarted-AnimationsTests.swift

@@ -53,8 +53,8 @@ class AnimationTests: XCTestCase {
     }
 
     self.mainQueue.advance(by: 1)
-    store.receive(.setColor(.white)) {
-      $0.circleColor = .white
+    store.receive(.setColor(.black)) {
+      $0.circleColor = .black
     }
 
     self.mainQueue.run()