Add support for default UIPageViewController animations

README.md

@@ -173,6 +173,8 @@ The following styles are available:
 - `.moveIn`
 - `.reveal`
 
+*Note: By default this is set to `nil`, which uses the standard animation provided by `UIPageViewController`.*
+
 ### Auto Scrolling
 `PageboyAutoScroller` is available to set up timer based automatic scrolling of the `PageboyViewController`:
 

Sources/Pageboy/Extensions/PageboyViewController+Management.swift

@@ -50,21 +50,27 @@ internal extension PageboyViewController {
 
         targetIndex = toIndex
         isUpdatingViewControllers = true
-        performTransition(from: fromIndex,
-                          to: toIndex,
-                          with: direction,
-                          animated: animated,
-                          completion: completion ?? { _ in })
 
+        let isUsingCustomTransition = transition != nil
+        if isUsingCustomTransition {
+            performTransition(from: fromIndex,
+                              to: toIndex,
+                              with: direction,
+                              animated: animated,
+                              completion: completion ?? { _ in })
+        }
+
+        // if not using a custom transition then animate using UIPageViewController mechanism
+        let animateUpdate = animated ? !isUsingCustomTransition : false
         let updateBlock = {
             pageViewController.setViewControllers(viewControllers,
                                                   direction: direction.pageViewControllerNavDirection,
-                                                  animated: false,
+                                                  animated: animateUpdate,
                                                   completion:
                 { (finished) in
                     self.isUpdatingViewControllers = false
 
-                    if !animated {
+                    if !animated || !isUsingCustomTransition {
                         completion?(finished)
                     }
             })

Sources/Pageboy/Extensions/PageboyViewController+Transitioning.swift

@@ -33,6 +33,7 @@ public extension PageboyViewController {
         public let duration: TimeInterval
 
         /// Default transition (Push, 0.3 second duration).
+        @available(*, obsoleted: 2.4.0, message:"To use the default transition, set PageboyViewController.transition to `nil`")
         public static var `default`: Transition {
             return Transition(style: .push, duration: 0.3)
         }
@@ -75,7 +76,7 @@ internal extension PageboyViewController {
     // MARK: Animation
 
     @objc func displayLinkDidTick() {
-        self.activeTransition?.tick()
+        self.activeTransitionOperation?.tick()
     }
 
     /// Perform a transition to a new page index.
@@ -91,11 +92,14 @@ internal extension PageboyViewController {
                                     with direction: NavigationDirection,
                                     animated: Bool,
                                     completion: @escaping TransitionOperation.Completion) {
-        guard animated == true, self.activeTransition == nil else {
-            return
+        guard let transition = self.transition,
+            animated == true,
+            self.activeTransitionOperation == nil else {
+                completion(false)
+                return
         }
         guard let scrollView = self.pageViewController?.scrollView else {
-            return
+            fatalError("Can't find UIPageViewController scroll view")
         }
 
         prepareForTransition()
@@ -112,13 +116,13 @@ internal extension PageboyViewController {
                                                 direction: direction,
                                                 semanticDirection: semanticDirection,
                                                 orientation: self.navigationOrientation)
-        self.activeTransition = TransitionOperation(for: self.transition,
+        self.activeTransitionOperation = TransitionOperation(for: transition,
                                                     action: action,
                                                     delegate: self)
         self.transitionDisplayLink?.isPaused = false
 
         // start transition
-        self.activeTransition?.start(on: scrollView.layer,
+        self.activeTransitionOperation?.start(on: scrollView.layer,
                                      completion: completion)
     }
 }
@@ -128,7 +132,7 @@ extension PageboyViewController: TransitionOperationDelegate {
     func transitionOperation(_ operation: TransitionOperation,
                              didFinish finished: Bool) {
         self.transitionDisplayLink?.isPaused = true
-        self.activeTransition = nil
+        self.activeTransitionOperation = nil
 
         clearUpAfterTransition()
     }

Sources/Pageboy/PageboyViewController.swift

@@ -154,12 +154,13 @@ open class PageboyViewController: UIViewController {
     /// Whether the view controllers in the page view controller are currently updating.
     internal var isUpdatingViewControllers: Bool = false
 
-    /// The transition to use when animating scrolls between pages.
-    public var transition = Transition.default
+    /// Custom transition to use when animating scrolls between pages.
+    /// Setting this to `nil` will revert to using the standard UIPageViewController animation.
+    public var transition: Transition?
     /// The display link for transitioning.
     internal var transitionDisplayLink: CADisplayLink?
     /// The active transition operation.
-    internal var activeTransition: TransitionOperation?
+    internal var activeTransitionOperation: TransitionOperation?
 
     /// The number of view controllers in the page view controller.
     internal var viewControllerCount: Int?
@@ -180,23 +181,7 @@ open class PageboyViewController: UIViewController {
             guard let currentIndex = self.currentIndex else {
                 return
             }
-
-            #if os(iOS)
-            UIView.animate(withDuration: 0.3) { 
-                self.setNeedsStatusBarAppearanceUpdate()
-            }
-            #endif
-
-            // ensure position keeps in sync
-            self.currentPosition = CGPoint(x: self.navigationOrientation == .horizontal ? CGFloat(currentIndex) : 0.0,
-                                           y: self.navigationOrientation == .vertical ? CGFloat(currentIndex) : 0.0)
-            let direction = NavigationDirection.forPosition(CGFloat(currentIndex),
-                                                            previous: CGFloat(oldValue ?? currentIndex))
-            self.delegate?.pageboyViewController(self,
-                                                 didScrollToPageAt: currentIndex,
-                                                 direction: direction,
-                                                 animated: self.isScrollingAnimated)
-
+            update(forNew: currentIndex, from: oldValue)
         }
     }
     /// The relative page position that the page view controller is currently at.
@@ -356,4 +341,23 @@ public extension PageboyViewController {
 
         return direction
     }
+
+    private func update(forNew currentIndex: PageIndex, from oldIndex: PageIndex?) {
+
+        #if os(iOS)
+            UIView.animate(withDuration: 0.3) {
+                self.setNeedsStatusBarAppearanceUpdate()
+            }
+        #endif
+
+        // ensure position keeps in sync
+        self.currentPosition = CGPoint(x: self.navigationOrientation == .horizontal ? CGFloat(currentIndex) : 0.0,
+                                       y: self.navigationOrientation == .vertical ? CGFloat(currentIndex) : 0.0)
+        let direction = NavigationDirection.forPosition(CGFloat(currentIndex),
+                                                        previous: CGFloat(oldIndex ?? currentIndex))
+        self.delegate?.pageboyViewController(self,
+                                             didScrollToPageAt: currentIndex,
+                                             direction: direction,
+                                             animated: self.isScrollingAnimated)
+    }
 }