fix：iOS11 or above may display wrong when scrolled to the end

EMPageViewController.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
   s.name             = "EMPageViewController"
-  s.version          = "4.0.0"
+  s.version          = "4.0.1"
   s.summary          = "A better page view controller for iOS."
   s.homepage         = "https://github.com/emalyak/EMPageViewController"
   s.license          = { :type => "MIT", :file => "LICENSE" }

EMPageViewController/EMPageViewController.swift

@@ -97,6 +97,10 @@ import UIKit
         - parameter transitionSuccessful: A Boolean whether the transition to the destination view controller was successful or not. If `true`, the new selected view controller is `destinationViewController`. If `false`, the transition returned to the view controller it started from, so the selected view controller is still `startingViewController`.
     */
     @objc optional func em_pageViewController(_ pageViewController: EMPageViewController, didFinishScrollingFrom startingViewController: UIViewController?, destinationViewController:UIViewController, transitionSuccessful: Bool)
+
+    @objc optional func em_pageViewController(_ pageViewController: EMPageViewController, scrollViewDidEndDragging: UIScrollView, willDecelerate decelerate: Bool)
+
+    @objc optional func em_pageViewController(_ pageViewController: EMPageViewController, scrollViewDidEndScrolling: UIScrollView)
 }
 
 /**
@@ -120,7 +124,7 @@ import UIKit
 }
 
 /// Manages page navigation between view controllers. View controllers can be navigated via swiping gestures, or called programmatically.
-open class EMPageViewController: UIViewController, UIScrollViewDelegate {
+open class EMPageViewController: UIViewController, UIScrollViewDelegate, UIGestureRecognizerDelegate {
 
     /// The object that provides view controllers on an as-needed basis throughout the navigation of the page view controller.
     ///
@@ -139,9 +143,13 @@ open class EMPageViewController: UIViewController, UIScrollViewDelegate {
         return self.navigationOrientation == .horizontal
     }
 
+    private var isChangeSize = false
+
+    @objc open var shouldRecognizeSimultaneously = false
+
     /// The underlying `UIScrollView` responsible for scrolling page views.
     /// - important: Properties should be set with caution to prevent unexpected behavior.
-    open private(set) lazy var scrollView: UIScrollView = {
+    @objc open private(set) lazy var scrollView: UIScrollView = {
         let scrollView = UIScrollView()
         scrollView.isPagingEnabled = true
         scrollView.scrollsToTop = false
@@ -152,17 +160,20 @@ open class EMPageViewController: UIViewController, UIScrollViewDelegate {
         scrollView.translatesAutoresizingMaskIntoConstraints = true
         scrollView.showsHorizontalScrollIndicator = false
         scrollView.showsVerticalScrollIndicator = false
+        if #available(iOS 11.0, *) {
+            scrollView.contentInsetAdjustmentBehavior = .never
+        }
         return scrollView
     }()
 
     /// The view controller before the selected view controller.
-    private var beforeViewController: UIViewController?
+    @objc open private(set) var beforeViewController: UIViewController?
 
     /// The currently selected view controller. Can be `nil` if no view controller is selected.
     @objc open private(set) var selectedViewController: UIViewController?
 
     /// The view controller after the selected view controller.
-    private var afterViewController: UIViewController?
+    @objc open private(set) var afterViewController: UIViewController?
 
     /// Boolean that indicates whether the page controller is currently in the process of scrolling.
     @objc open private(set) var scrolling = false
@@ -180,7 +191,7 @@ open class EMPageViewController: UIViewController, UIScrollViewDelegate {
     /// Initializes a newly created page view controller with the specified navigation orientation.
     /// - parameter navigationOrientation: The page view controller's navigation scroll direction.
     /// - returns: The initialized page view controller.
-    public convenience init(navigationOrientation: EMPageViewControllerNavigationOrientation) {
+    @objc public convenience init(navigationOrientation: EMPageViewControllerNavigationOrientation) {
         self.init()
         self.navigationOrientation = navigationOrientation
     }
@@ -199,19 +210,61 @@ open class EMPageViewController: UIViewController, UIScrollViewDelegate {
     @objc open func selectViewController(_ viewController: UIViewController, direction: EMPageViewControllerNavigationDirection, animated: Bool, completion: ((_ transitionSuccessful: Bool) -> Void)?) {
 
         if (direction == .forward) {
-            self.afterViewController = viewController
+            if afterViewController != viewController {
+                removeChildIfNeeded(afterViewController)
+                afterViewController = viewController
+            }
             self.layoutViews()
             self.loadNewAdjoiningViewControllersOnFinish = true
             self.scrollForward(animated: animated, completion: completion)
         } else if (direction == .reverse) {
-            self.beforeViewController = viewController
+            if beforeViewController != viewController {
+                removeChildIfNeeded(beforeViewController)
+                beforeViewController = viewController
+            }
             self.layoutViews()
             self.loadNewAdjoiningViewControllersOnFinish = true
             self.scrollReverse(animated: animated, completion: completion)
         }
 
     }
 
+    /**
+     remove all controllers, so that can be reloaded
+     */
+    @objc open func removeViewControllers() {
+        guard !scrolling else { return }
+        removeChildIfNeeded(beforeViewController)
+        removeChildIfNeeded(afterViewController)
+        removeChildIfNeeded(selectedViewController)
+        beforeViewController = nil
+        afterViewController = nil
+        selectedViewController = nil
+    }
+
+    /**
+     allow load after ViewController when new data added to dataSource, call this method when scrolling is false
+     */
+    @objc open func loadAfterViewControllerIfPossible() {
+        guard !scrolling, nil == afterViewController,
+              let current = selectedViewController else { return }
+        loadAfterViewController(for: current)
+        if nil != afterViewController {
+            layoutViews()
+        }
+    }
+
+    /**
+     allow load before ViewController when new data added to dataSource, call this method when scrolling is false
+     */
+    @objc open func loadBeforeViewControllerIfPossible() {
+        guard !scrolling, nil == beforeViewController,
+              let current = selectedViewController else { return }
+        loadBeforeViewController(for: current)
+        if nil != beforeViewController {
+            layoutViews()
+        }
+    }
 
     /**
      Transitions to the view controller right of the currently selected view controller in a horizontal orientation, or below the currently selected view controller in a vertical orientation. Also described as going to the next page.
@@ -295,7 +348,7 @@ open class EMPageViewController: UIViewController, UIScrollViewDelegate {
     open override func viewWillLayoutSubviews() {
         super.viewWillLayoutSubviews()
 
-        guard !scrolling else {
+        guard !scrolling || isChangeSize else {
             return
         }
 
@@ -519,11 +572,16 @@ open class EMPageViewController: UIViewController, UIScrollViewDelegate {
         self.layoutViews()
     }
 
+    // MARK: - UIGestureRecognizerDelegate
+
+    func gestureRecognizer(_ gesture: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGesture: UIGestureRecognizer) -> Bool {
+        return shouldRecognizeSimultaneously
+    }
 
     // MARK: - UIScrollView Delegate
 
     open func scrollViewDidScroll(_ scrollView: UIScrollView) {
-        if !adjustingContentOffset {
+        if !adjustingContentOffset && !isChangeSize {
 
             let distance = self.isOrientationHorizontal ? self.view.bounds.width : self.view.bounds.height
             let progress = ((self.isOrientationHorizontal ? scrollView.contentOffset.x : scrollView.contentOffset.y) - distance) / distance
@@ -603,14 +661,41 @@ open class EMPageViewController: UIViewController, UIScrollViewDelegate {
                 (self.afterViewController != nil && self.beforeViewController == nil && scrollView.contentOffset.x > abs(scrollView.contentInset.left)) || // If it's at the beginning of the collection, the decelleration can't be triggered by scrolling away from, than torwards the inset
                 (self.beforeViewController != nil && self.afterViewController == nil && scrollView.contentOffset.x < abs(scrollView.contentInset.right)) { // Same as the last condition, but at the end of the collection
                     scrollView.setContentOffset(CGPoint(x: self.view.bounds.width, y: 0), animated: true)
+            } else {
+                delegate?.em_pageViewController?(self, scrollViewDidEndScrolling: scrollView)
             }
         } else {
             if  (self.beforeViewController != nil && self.afterViewController != nil) || // It isn't at the beginning or end of the page collection
                 (self.afterViewController != nil && self.beforeViewController == nil && scrollView.contentOffset.y > abs(scrollView.contentInset.top)) || // If it's at the beginning of the collection, the decelleration can't be triggered by scrolling away from, than torwards the inset
                 (self.beforeViewController != nil && self.afterViewController == nil && scrollView.contentOffset.y < abs(scrollView.contentInset.bottom)) { // Same as the last condition, but at the end of the collection
                     scrollView.setContentOffset(CGPoint(x: 0, y: self.view.bounds.height), animated: true)
+            } else {
+                delegate?.em_pageViewController?(self, scrollViewDidEndScrolling: scrollView)
             }
         }
+    }
+
+    public func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
+        delegate?.em_pageViewController?(self, scrollViewDidEndDragging: scrollView, willDecelerate: decelerate)
+        if !decelerate {
+            delegate?.em_pageViewController?(self, scrollViewDidEndScrolling: scrollView)
+        }
+    }
+
+    public func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
+        delegate?.em_pageViewController?(self, scrollViewDidEndScrolling: scrollView)
+    }
+
+    // MARK: - size change
+    open override func viewWillTransition(to size: CGSize, with coordinator: any UIViewControllerTransitionCoordinator) {
 
+        self.isChangeSize = true
+
+        super.viewWillTransition(to: size, with: coordinator)
+        coordinator.animate { [weak self] _ in
+            self?.view.setNeedsLayout()
+        } completion: { [weak self] _ in
+            self?.isChangeSize = false
+        }
     }
 }