Fix swipe back cancellation leaving views in inconsistent state (#78)

Author: davdroman

Sources/Animator/AnimatorTransientView.swift

@@ -47,7 +47,14 @@ public class AnimatorTransientView {
 		self.uiView = uiView
 	}
 
-	@_spi(package) public func setUIViewProperties(to properties: KeyPath<AnimatorTransientView, Properties>) {
-		self[keyPath: properties].assignToUIView(uiView)
+	@_spi(package) public func setUIViewProperties(
+		to properties: KeyPath<AnimatorTransientView, Properties>,
+		force: Bool = false
+	) {
+		self[keyPath: properties].assignToUIView(uiView, force: force)
+	}
+
+	@_spi(package) public func resetUIViewProperties() {
+		Properties.default.assignToUIView(uiView, force: true)
 	}
 }

Sources/Animator/AnimatorTransientViewProperties.swift

@@ -16,6 +16,12 @@ public struct AnimatorTransientViewProperties: Equatable {
 }
 
 extension AnimatorTransientViewProperties {
+	static let `default` = Self(
+		alpha: 1,
+		transform: .identity,
+		zPosition: 0
+	)
+
 	init(of uiView: UIView) {
 		self.init(
 			alpha: uiView.alpha,
@@ -24,9 +30,9 @@ extension AnimatorTransientViewProperties {
 		)
 	}
 
-	func assignToUIView(_ uiView: UIView) {
-		$alpha.assignTo(uiView, \.alpha)
-		$transform?.assignToUIView(uiView)
-		$zPosition.assignTo(uiView, \.layer.zPosition)
+	func assignToUIView(_ uiView: UIView, force: Bool) {
+		$alpha.assign(to: uiView, \.alpha, force: force)
+		$transform.assign(to: uiView, force: force)
+		$zPosition.assign(to: uiView, \.layer.zPosition, force: force)
 	}
 }

Sources/Animator/OptionalWithDefault.swift

@@ -1,12 +1,13 @@
 @propertyWrapper
 public struct OptionalWithDefault<Value> {
-	public private(set) var projectedValue: Value? = nil
+	public var projectedValue: Self { self }
 
-	private var defaultValue: Value
+	public private(set) var value: Value? = nil
+	public private(set) var defaultValue: Value
 
 	public var wrappedValue: Value {
-		get { projectedValue ?? defaultValue }
-		set { projectedValue = newValue }
+		get { value ?? defaultValue }
+		set { value = newValue }
 	}
 
 	public init(wrappedValue: Value) {
@@ -16,10 +17,20 @@ public struct OptionalWithDefault<Value> {
 
 extension OptionalWithDefault: Equatable where Value: Equatable {}
 
-extension Optional {
-	func assignTo<Root: AnyObject>(_ root: Root, _ valueKeyPath: ReferenceWritableKeyPath<Root, Wrapped>) {
-		if let value = self {
-			root[keyPath: valueKeyPath] = value
+extension OptionalWithDefault {
+	func assign<Root: AnyObject>(to root: Root, _ valueKeyPath: ReferenceWritableKeyPath<Root, Value>, force: Bool) {
+		assign(force: force) { root[keyPath: valueKeyPath] = $0 }
+	}
+
+	func assign(force: Bool, handler: (Value) -> Void) {
+		if let value = { () -> Value? in
+			if force {
+				return wrappedValue
+			} else {
+				return value
+			}
+		}() {
+			handler(value)
 		}
 	}
 }

Sources/Animator/Transform.swift

@@ -2,7 +2,7 @@ import UIKit
 
 @dynamicMemberLookup
 public struct Transform: Equatable {
-	private var transform: CATransform3D
+	fileprivate var transform: CATransform3D
 
 	public subscript<T>(dynamicMember keyPath: WritableKeyPath<CATransform3D, T>) -> T {
 		get { transform[keyPath: keyPath] }
@@ -12,12 +12,16 @@ public struct Transform: Equatable {
 	init(_ transform: CATransform3D) {
 		self.transform = transform
 	}
+}
 
-	func assignToUIView(_ uiView: UIView) {
-		if let transform = transform.affineTransform {
-			uiView.transform = transform
-		} else {
-			uiView.transform3D = transform
+extension OptionalWithDefault where Value == Transform {
+	func assign(to uiView: UIView, force: Bool) {
+		self.assign(force: force) {
+			if let transform = $0.transform.affineTransform {
+				uiView.transform = transform
+			} else {
+				uiView.transform3D = $0.transform
+			}
 		}
 	}
 }

Sources/NavigationTransitions/NavigationTransitionDelegate.swift

@@ -89,25 +89,54 @@ final class NavigationTransitionAnimatorProvider: NSObject, UIViewControllerAnim
 		)
 		cachedAnimators[ObjectIdentifier(transitionContext)] = animator
 
+		let container = transitionContext.containerView
+		guard
+			let fromUIView = transitionContext.view(forKey: .from),
+			let toUIView = transitionContext.view(forKey: .to)
+		else {
+			return animator
+		}
+
+		fromUIView.isUserInteractionEnabled = false
+		toUIView.isUserInteractionEnabled = false
+
 		switch transition.handler {
 		case .transient(let handler):
-			if let (fromView, toView) = transientViews(for: handler, animator: animator, context: transitionContext) {
-				fromView.setUIViewProperties(to: \.initial)
-				animator.addAnimations { fromView.setUIViewProperties(to: \.animation) }
-				animator.addCompletion { _ in fromView.setUIViewProperties(to: \.completion) }
-
-				toView.setUIViewProperties(to: \.initial)
-				animator.addAnimations { toView.setUIViewProperties(to: \.animation) }
-				animator.addCompletion { _ in toView.setUIViewProperties(to: \.completion) }
+			if let (fromView, toView) = transientViews(
+				for: handler,
+				animator: animator,
+				context: (container, fromUIView, toUIView)
+			) {
+				for view in [fromView, toView] {
+					view.setUIViewProperties(to: \.initial)
+					animator.addAnimations { view.setUIViewProperties(to: \.animation) }
+					animator.addCompletion { _ in
+						if transitionContext.transitionWasCancelled {
+							view.resetUIViewProperties()
+						} else {
+							view.setUIViewProperties(to: \.completion)
+						}
+					}
+				}
 			}
 		case .primitive(let handler):
 			handler(animator, operation, transitionContext)
 		}
 
 		animator.addCompletion { _ in
 			transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
-			transitionContext.view(forKey: .from)?.isUserInteractionEnabled = true
-			transitionContext.view(forKey: .to)?.isUserInteractionEnabled = true
+
+			fromUIView.isUserInteractionEnabled = true
+			toUIView.isUserInteractionEnabled = true
+
+			// iOS 16 workaround to nudge views into becoming responsive after transition
+			if transitionContext.transitionWasCancelled {
+				fromUIView.removeFromSuperview()
+				container.addSubview(fromUIView)
+			} else {
+				toUIView.removeFromSuperview()
+				container.addSubview(toUIView)
+			}
 		}
 
 		return animator
@@ -116,19 +145,10 @@ final class NavigationTransitionAnimatorProvider: NSObject, UIViewControllerAnim
 	private func transientViews(
 		for handler: AnyNavigationTransition.TransientHandler,
 		animator: Animator,
-		context: UIViewControllerContextTransitioning
+		context: (container: UIView, fromUIView: UIView, toUIView: UIView)
 	) -> (fromView: AnimatorTransientView, toView: AnimatorTransientView)? {
-		guard
-			let fromUIView = context.view(forKey: .from),
-			let toUIView = context.view(forKey: .to)
-		else {
-			return nil
-		}
-
-		fromUIView.isUserInteractionEnabled = false
-		toUIView.isUserInteractionEnabled = false
+		let (container, fromUIView, toUIView) = context
 
-		let container = context.containerView
 		switch operation {
 		case .push:
 			container.insertSubview(toUIView, aboveSubview: fromUIView)
@@ -141,6 +161,6 @@ final class NavigationTransitionAnimatorProvider: NSObject, UIViewControllerAnim
 
 		handler(fromView, toView, operation, container)
 
-		return (fromView: fromView, toView: toView)
+		return (fromView, toView)
 	}
 }

Sources/TestUtils/AnimatorTransientView+Mocks.swift

@@ -48,7 +48,10 @@ final class UnimplementedAnimatorTransientView: AnimatorTransientView {
 		super.init(UIView())
 	}
 
-	override public func setUIViewProperties(to properties: KeyPath<AnimatorTransientView, AnimatorTransientView.Properties>) {
+	override public func setUIViewProperties(
+		to properties: KeyPath<AnimatorTransientView, AnimatorTransientView.Properties>,
+		force: Bool
+	) {
 		XCTFail("\(Self.self).\(#function) is unimplemented")
 	}
 }

Tests/AnimatorTests/AnimatorTransientViewPropertiesTests.swift

@@ -16,9 +16,26 @@ extension AnimatorTransientViewPropertiesTests {
 		sut.transform = .init(.identity.scaled(5))
 		sut.zPosition = 15
 
-		sut.assignToUIView(view)
+		sut.assignToUIView(view, force: false)
 		XCTAssertEqual(view.alpha, 0.5)
 		XCTAssertEqual(view.transform3D, .identity.scaled(5))
 		XCTAssertEqual(view.layer.zPosition, 15)
 	}
+
+	func testForceAssignToUIView() {
+		let view = UIView()
+		view.transform = .identity.scaledBy(x: 5, y: 5)
+		view.layer.zPosition = 15
+		XCTAssertEqual(view.alpha, 1)
+		XCTAssertEqual(view.transform, .identity.scaledBy(x: 5, y: 5))
+		XCTAssertEqual(view.layer.zPosition, 15)
+
+		var sut = AnimatorTransientView.Properties.default
+		sut.alpha = 0.5
+
+		sut.assignToUIView(view, force: true)
+		XCTAssertEqual(view.alpha, 0.5)
+		XCTAssertEqual(view.transform3D, .identity)
+		XCTAssertEqual(view.layer.zPosition, 0)
+	}
 }