Add ViewEnvironment (#739)

ViewEnvironment is a container of strongly-typed key/value pairs that can be
passed down the view-side of a workflow tree. This allows containers to provide
view-oriented hinting to their children as well as allows for view-side changes
to view-only environment without re-rendering the workflow tree (for example,
runtime theme changes).

swift/Samples/BackStackContainer/Sources/BackStackContainer.swift

@@ -19,10 +19,10 @@ import WorkflowUI
 public final class BackStackContainer: ScreenViewController<BackStackScreen>, UINavigationControllerDelegate {
     private let navController: UINavigationController
 
-    public required init(screen: BackStackScreen) {
+    public required init(screen: BackStackScreen, environment: ViewEnvironment) {
         self.navController = UINavigationController()
 
-        super.init(screen: screen)
+        super.init(screen: screen, environment: environment)
 
         update(with: screen)
     }
@@ -42,7 +42,7 @@ public final class BackStackContainer: ScreenViewController<BackStackScreen>, UI
         navController.view.frame = view.bounds
     }
 
-    public override func screenDidChange(from previousScreen: BackStackScreen) {
+    public override func screenDidChange(from previousScreen: BackStackScreen, previousEnvironment: ViewEnvironment) {
         update(with: screen)
     }
 
@@ -63,10 +63,10 @@ public final class BackStackContainer: ScreenViewController<BackStackScreen>, UI
                 viewController.matches(item: item)
             }) {
                 let existingViewController = existingViewControllers.remove(at: idx)
-                existingViewController.update(item: item)
+                existingViewController.update(item: item, environment: environment)
                 updatedViewControllers.append(existingViewController)
             } else {
-                updatedViewControllers.append(ScreenWrapperViewController(item: item))
+                updatedViewControllers.append(ScreenWrapperViewController(item: item, environment: environment))
             }
 
         }

swift/Samples/BackStackContainer/Sources/BackStackScreen.swift

@@ -23,8 +23,8 @@ public struct BackStackScreen: Screen {
         self.items = items
     }
 
-    public var viewControllerDescription: ViewControllerDescription {
-        return BackStackContainer.description(for: self)
+    public func viewControllerDescription(environment: ViewEnvironment) -> ViewControllerDescription {
+        return BackStackContainer.description(for: self, environment: environment)
     }
 }
 

swift/Samples/BackStackContainer/Sources/ScreenWrapperViewController.swift

@@ -22,13 +22,15 @@ import WorkflowUI
 final class ScreenWrapperViewController: UIViewController {
     let key: AnyHashable
     let screenType: Any.Type
+    let environment: ViewEnvironment
 
     let contentViewController: DescribedViewController
 
-    init(item: BackStackScreen.Item) {
+    init(item: BackStackScreen.Item, environment: ViewEnvironment) {
         self.key = item.key
         self.screenType = item.screenType
-        self.contentViewController = DescribedViewController(screen: item.screen)
+        self.environment = environment
+        self.contentViewController = DescribedViewController(screen: item.screen, environment: environment)
 
         super.init(nibName: nil, bundle: nil)
 
@@ -51,8 +53,8 @@ final class ScreenWrapperViewController: UIViewController {
         contentViewController.view.frame = view.bounds
     }
 
-    func update(item: BackStackScreen.Item) {
-        contentViewController.update(screen: item.screen)
+    func update(item: BackStackScreen.Item, environment: ViewEnvironment) {
+        contentViewController.update(screen: item.screen, environment: environment)
         update(barVisibility: item.barVisibility)
     }
 

swift/Samples/SampleApp/Sources/CrossFadeContainer.swift

@@ -39,18 +39,18 @@ struct CrossFadeScreen: Screen {
         return self.key == otherScreen.key
     }
 
-    var viewControllerDescription: ViewControllerDescription {
-        return CrossFadeContainerViewController.description(for: self)
+    func viewControllerDescription(environment: ViewEnvironment) -> ViewControllerDescription {
+        return CrossFadeContainerViewController.description(for: self, environment: environment)
     }
 }
 
 
 fileprivate final class CrossFadeContainerViewController: ScreenViewController<CrossFadeScreen> {
     var childViewController: DescribedViewController
 
-    required init(screen: CrossFadeScreen) {
-        childViewController = DescribedViewController(screen: screen.baseScreen)
-        super.init(screen: screen)
+    required init(screen: CrossFadeScreen, environment: ViewEnvironment) {
+        childViewController = DescribedViewController(screen: screen.baseScreen, environment: environment)
+        super.init(screen: screen, environment: environment)
     }
 
     override func viewDidLoad() {
@@ -67,13 +67,13 @@ fileprivate final class CrossFadeContainerViewController: ScreenViewController<C
         childViewController.view.frame = view.bounds
     }
 
-    override func screenDidChange(from previousScreen: CrossFadeScreen) {
+    override func screenDidChange(from previousScreen: CrossFadeScreen, previousEnvironment: ViewEnvironment) {
         if screen.isEquivalent(to: previousScreen) {
-            childViewController.update(screen: screen.baseScreen)
+            childViewController.update(screen: screen.baseScreen, environment: environment)
         } else {
             // The new screen is different than the previous. Animate the transition.
             let oldChild = childViewController
-            childViewController = DescribedViewController(screen: screen.baseScreen)
+            childViewController = DescribedViewController(screen: screen.baseScreen, environment: environment)
             addChild(childViewController)
             view.addSubview(childViewController.view)
             UIView.transition(

swift/Samples/SampleApp/Sources/DemoScreen.swift

@@ -29,8 +29,8 @@ struct DemoScreen: Screen {
     let isRefreshEnabled: Bool
     let onRefreshTap: () -> Void
 
-    var viewControllerDescription: ViewControllerDescription {
-        return DemoViewController.description(for: self)
+    func viewControllerDescription(environment: ViewEnvironment) -> ViewControllerDescription {
+        return DemoViewController.description(for: self, environment: environment)
     }
 }
 
@@ -42,12 +42,12 @@ fileprivate final class DemoViewController: ScreenViewController<DemoScreen> {
     private let statusLabel: UILabel
     private let refreshButton: UIButton
 
-    required init(screen: DemoScreen) {
+    required init(screen: DemoScreen, environment: ViewEnvironment) {
         titleButton = UIButton(frame: .zero)
         subscribeButton = UIButton(frame: .zero)
         statusLabel = UILabel(frame: .zero)
         refreshButton = UIButton(frame: .zero)
-        super.init(screen: screen)
+        super.init(screen: screen, environment: environment)
 
         update(with: screen)
     }
@@ -106,7 +106,7 @@ fileprivate final class DemoViewController: ScreenViewController<DemoScreen> {
             height: height)
     }
 
-    override func screenDidChange(from previousScreen: DemoScreen) {
+    override func screenDidChange(from previousScreen: DemoScreen, previousEnvironment: ViewEnvironment) {
         update(with: screen)
     }
 

swift/Samples/SampleApp/Sources/WelcomeScreen.swift

@@ -22,8 +22,8 @@ struct WelcomeScreen: Screen {
     var onNameChanged: (String) -> Void
     var onLoginTapped: () -> Void
 
-    var viewControllerDescription: ViewControllerDescription {
-        return WelcomeViewController.description(for: self)
+    func viewControllerDescription(environment: ViewEnvironment) -> ViewControllerDescription {
+        return WelcomeViewController.description(for: self, environment: environment)
     }
 }
 
@@ -33,11 +33,11 @@ fileprivate final class WelcomeViewController: ScreenViewController<WelcomeScree
     let nameField: UITextField
     let button: UIButton
 
-    required init(screen: WelcomeScreen) {
+    required init(screen: WelcomeScreen, environment: ViewEnvironment) {
         welcomeLabel = UILabel(frame: .zero)
         nameField = UITextField(frame: .zero)
         button = UIButton(frame: .zero)
-        super.init(screen: screen)
+        super.init(screen: screen, environment: environment)
 
         update(with: screen)
     }
@@ -89,7 +89,7 @@ fileprivate final class WelcomeViewController: ScreenViewController<WelcomeScree
             .insetBy(dx: inset, dy: 0.0)
     }
 
-    override func screenDidChange(from previousScreen: WelcomeScreen) {
+    override func screenDidChange(from previousScreen: WelcomeScreen, previousEnvironment: ViewEnvironment) {
         update(with: screen)
     }
 

swift/Samples/SplitScreenContainer/DemoApp/BarScreen.swift

@@ -22,8 +22,8 @@ struct BarScreen: Screen {
     let backgroundColors: [UIColor]
     let viewTapped: () -> Void
 
-    var viewControllerDescription: ViewControllerDescription {
-        return BarScreenViewController.description(for: self)
+    func viewControllerDescription(environment: ViewEnvironment) -> ViewControllerDescription {
+        return BarScreenViewController.description(for: self, environment: environment)
     }
 }
 
@@ -34,8 +34,8 @@ fileprivate final class BarScreenViewController: ScreenViewController<BarScreen>
     private lazy var tapGestureRecognizer: UITapGestureRecognizer = .init()
     private var gradientLayer: CAGradientLayer?
 
-    required init(screen: BarScreen) {
-        super.init(screen: screen)
+    required init(screen: BarScreen, environment: ViewEnvironment) {
+        super.init(screen: screen, environment: environment)
 
         update(with: screen)
     }
@@ -58,8 +58,8 @@ fileprivate final class BarScreenViewController: ScreenViewController<BarScreen>
 
         updateGradient(for: view, colors: screen.backgroundColors)
     }
-    
-    override func screenDidChange(from previousScreen: BarScreen) {
+
+    override func screenDidChange(from previousScreen: BarScreen, previousEnvironment: ViewEnvironment) {
         update(with: screen)
     }
 

swift/Samples/SplitScreenContainer/DemoApp/FooScreen.swift

@@ -22,8 +22,8 @@ struct FooScreen: Screen {
     let backgroundColor: UIColor
     let viewTapped: () -> Void
 
-    var viewControllerDescription: ViewControllerDescription {
-        return FooScreenViewController.description(for: self)
+    func viewControllerDescription(environment: ViewEnvironment) -> ViewControllerDescription {
+        return FooScreenViewController.description(for: self, environment: environment)
     }
 }
 
@@ -33,8 +33,8 @@ fileprivate final class FooScreenViewController: ScreenViewController<FooScreen>
     private lazy var titleLabel: UILabel = .init()
     private lazy var tapGestureRecognizer: UITapGestureRecognizer = .init()
 
-    required init(screen: FooScreen) {
-        super.init(screen: screen)
+    required init(screen: FooScreen, environment: ViewEnvironment) {
+        super.init(screen: screen, environment: environment)
 
         update(with: screen)
     }
@@ -54,8 +54,8 @@ fileprivate final class FooScreenViewController: ScreenViewController<FooScreen>
             titleLabel.centerYAnchor.constraint(equalTo: view.centerYAnchor),
         ])
     }
-    
-    override func screenDidChange(from previousScreen: FooScreen) {
+
+    override func screenDidChange(from previousScreen: FooScreen, previousEnvironment: ViewEnvironment) {
         update(with: screen)
     }
 

swift/Samples/SplitScreenContainer/SnapshotTests/SplitScreenContainerScreenSnapshotTests.swift

@@ -29,7 +29,8 @@ class SplitScreenContainerScreenSnapshotTests: FBSnapshotTestCase {
             )
 
             let viewController = SplitScreenContainerViewController(
-                screen: splitScreenContainerScreen
+                screen: splitScreenContainerScreen,
+                environment: .empty
             )
             viewController.view.layoutIfNeeded()
 
@@ -44,8 +45,8 @@ fileprivate struct FooScreen: Screen {
     let backgroundColor: UIColor
     let viewTapped: () -> Void
 
-    var viewControllerDescription: ViewControllerDescription {
-        return FooScreenViewController.description(for: self)
+    func viewControllerDescription(environment: ViewEnvironment) -> ViewControllerDescription {
+        return FooScreenViewController.description(for: self, environment: environment)
     }
 }
 
@@ -55,8 +56,8 @@ fileprivate final class FooScreenViewController: ScreenViewController<FooScreen>
     private lazy var titleLabel: UILabel = .init()
     private lazy var tapGestureRecognizer: UITapGestureRecognizer = .init()
 
-    required init(screen: FooScreen) {
-        super.init(screen: screen)
+    required init(screen: FooScreen, environment: ViewEnvironment) {
+        super.init(screen: screen, environment: environment)
 
         update(with: screen)
     }
@@ -76,8 +77,8 @@ fileprivate final class FooScreenViewController: ScreenViewController<FooScreen>
             titleLabel.centerYAnchor.constraint(equalTo: view.centerYAnchor),
             ])
     }
-    
-    override func screenDidChange(from previousScreen: FooScreen) {
+
+    override func screenDidChange(from previousScreen: FooScreen, previousEnvironment: ViewEnvironment) {
         update(with: screen)
     }
 

swift/Samples/SplitScreenContainer/Sources/Environment+SplitScreen.swift

@@ -0,0 +1,41 @@
+/*
+* Copyright 2020 Square Inc.
+*
+* Licensed under the Apache License, Version 2.0 (the "License");
+* you may not use this file except in compliance with the License.
+* You may obtain a copy of the License at
+*
+*     http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software
+* distributed under the License is distributed on an "AS IS" BASIS,
+* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+* See the License for the specific language governing permissions and
+* limitations under the License.
+*/
+
+import WorkflowUI
+
+public enum SplitScreenPosition {
+    /// Not appearing in a split screen context
+    case none
+
+    /// Appearing in the leading position in a split screen
+    case leading
+
+    /// Appearing in the trailing position in a split screen
+    case trailing
+}
+
+extension ViewEnvironment {
+
+    internal(set) public var splitScreenPosition: SplitScreenPosition {
+        get { return self[SplitScreenPositionKey.self] }
+        set { self[SplitScreenPositionKey.self] = newValue }
+    }
+
+}
+
+private enum SplitScreenPositionKey: ViewEnvironmentKey {
+    static var defaultValue: SplitScreenPosition = .none
+}

swift/Samples/SplitScreenContainer/Sources/SplitScreenContainerScreen.swift

@@ -48,8 +48,8 @@ public struct SplitScreenContainerScreen<LeadingScreenType: Screen, TrailingScre
         self.separatorWidth = separatorWidth
     }
 
-    public var viewControllerDescription: ViewControllerDescription {
-        return SplitScreenContainerViewController.description(for: self)
+    public func viewControllerDescription(environment: ViewEnvironment) -> ViewControllerDescription {
+        return SplitScreenContainerViewController.description(for: self, environment: environment)
     }
 
 }

swift/Samples/SplitScreenContainer/Sources/SplitScreenContainerViewController.swift

@@ -29,13 +29,21 @@ internal final class SplitScreenContainerViewController<LeadingScreenType: Scree
 
     private var needsAnimatedLayout = false
 
-    required init(screen: ContainerScreen) {
-        leadingContentViewController = DescribedViewController(screen: screen.leadingScreen)
-        trailingContentViewController = DescribedViewController(screen: screen.trailingScreen)
-        super.init(screen: screen)
+    required init(screen: ContainerScreen, environment: ViewEnvironment) {
+        leadingContentViewController = DescribedViewController(
+            screen: screen.leadingScreen,
+            environment: environment
+                .setting(keyPath: \.splitScreenPosition, to: .leading)
+        )
+        trailingContentViewController = DescribedViewController(
+            screen: screen.trailingScreen,
+            environment: environment
+                .setting(keyPath: \.splitScreenPosition, to: .trailing)
+        )
+        super.init(screen: screen, environment: environment)
     }
 
-    override internal func screenDidChange(from previousScreen: ContainerScreen) {
+    override internal func screenDidChange(from previousScreen: ContainerScreen, previousEnvironment: ViewEnvironment) {
         if screen.ratio != previousScreen.ratio {
             needsAnimatedLayout = true
         }
@@ -48,8 +56,16 @@ internal final class SplitScreenContainerViewController<LeadingScreenType: Scree
     private func update(with screen: ContainerScreen) {
         separatorView.backgroundColor = screen.separatorColor
 
-        leadingContentViewController.update(screen: screen.leadingScreen)
-        trailingContentViewController.update(screen: screen.trailingScreen)
+        leadingContentViewController.update(
+            screen: screen.leadingScreen,
+            environment: environment
+                .setting(keyPath: \.splitScreenPosition, to: .leading)
+        )
+        trailingContentViewController.update(
+            screen: screen.trailingScreen,
+            environment: environment
+                .setting(keyPath: \.splitScreenPosition, to: .trailing)
+        )
 
         //Intentional force of layout pass after updating the child view controllers
         view.layoutIfNeeded()