Use content offset observation instead of delegate methods to update content offsets

Sources/SimultaneouslyScrollView/DefaultSimultaneouslyScrollViewHandler.swift

@@ -6,6 +6,7 @@ internal class DefaultSimultaneouslyScrollViewHandler: NSObject, SimultaneouslyS
     private var scrollViewsStore: [ScrollViewDecorator] = []
     private weak var lastScrollingScrollView: UIScrollView?
 
+    private var cancellables: Set<AnyCancellable> = []
     private let scrolledToBottomSubject = PassthroughSubject<Bool, Never>()
 
     var scrolledToBottomPublisher: AnyPublisher<Bool, Never> {
@@ -21,36 +22,30 @@ internal class DefaultSimultaneouslyScrollViewHandler: NSObject, SimultaneouslyS
             return
         }
 
-        let currentDelegate: UIScrollViewDelegate? = scrollView.delegate
-
-        let multicastDelegate = {
-            if let multicastDelegate = scrollView.delegate as? MulticastScrollViewDelegate {
-                return multicastDelegate
-            } else {
-                let multicastDelegate = MulticastScrollViewDelegate()
-                if let currentDelegate {
-                    multicastDelegate.addDelegate(currentDelegate)
-                }
-                scrollView.delegate = multicastDelegate
-                return multicastDelegate
-            }
-        }()
-
-        multicastDelegate.addDelegate(self)
-
         scrollViewsStore.append(
             ScrollViewDecorator(
                 scrollView: scrollView,
-                delegate: multicastDelegate,
+                handler: self,
                 directions: scrollDirections
             )
         )
-
+
+        scrollViewsStore.removeAll(where: {$0.scrollView == nil})
+
         // Scroll the new `ScrollView` to the current position of the others.
         // Using the first `ScrollView` should be enough as all should be synchronized at this point already.
         guard let decorator = scrollViewsStore.first else {
             return
         }
+
+        scrollView.publisher(for: \.contentOffset)
+            .scan((old: scrollView.contentOffset, new: scrollView.contentOffset)) { (old: $0.new, new: $1) }
+            .sink { [weak self, weak scrollView] in
+                if let self, let scrollView {
+                    self.handleContentOffsetChange(for: scrollView, oldValue: $0.old)
+                }
+            }
+            .store(in: &cancellables)
 
         sync(scrollView: scrollView, with: decorator)
 
@@ -107,23 +102,30 @@ internal class DefaultSimultaneouslyScrollViewHandler: NSObject, SimultaneouslyS
             registeredScrollView.setContentOffset(scrollView.contentOffset, animated: false)
         }
     }
+
+    var isUpdatingContentOffset: Bool = false
 }
 
 extension DefaultSimultaneouslyScrollViewHandler: UIScrollViewDelegate {
-    func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
-        lastScrollingScrollView = scrollView
-    }
-
-    func scrollViewDidScroll(_ scrollView: UIScrollView) {
+    func handleContentOffsetChange(for scrollView: UIScrollView, oldValue: CGPoint?) {
         checkIsContentOffsetAtBottom()
-
-        guard lastScrollingScrollView == scrollView else {
+        
+        guard oldValue != scrollView.contentOffset else {
             return
         }
-
+
+        guard !isUpdatingContentOffset else {
+            return
+        }
+
+        isUpdatingContentOffset = true
+        defer { isUpdatingContentOffset = false }
+
         scrollViewsStore
-            .filter { $0.scrollView != lastScrollingScrollView }
-            .forEach { sync(scrollView: scrollView, with: $0) }
+            .filter { $0.scrollView != scrollView }
+            .forEach {
+                sync(scrollView: scrollView, with: $0)
+            }
     }
 }
 #endif

Sources/SimultaneouslyScrollView/Helper/ScrollViewDecorator.swift

@@ -4,16 +4,16 @@ import UIKit
 
 internal class ScrollViewDecorator {
     weak var scrollView: UIScrollView?
-    var delegate: MulticastScrollViewDelegate
+    weak var handler: DefaultSimultaneouslyScrollViewHandler?
     var directions: SimultaneouslyScrollViewDirection?
-
+    
     init(
         scrollView: UIScrollView,
-        delegate: MulticastScrollViewDelegate,
+        handler: DefaultSimultaneouslyScrollViewHandler?,
         directions: SimultaneouslyScrollViewDirection?
     ) {
         self.scrollView = scrollView
-        self.delegate = delegate
+        self.handler = handler
         self.directions = directions
     }
 }