fix: emit onPageScroll with zero offset on idle to prevent indicator jump (#1076)

Author: MrRefactor

android/src/main/java/com/reactnativepagerview/PagerViewViewManager.kt

@@ -75,6 +75,13 @@ class PagerViewViewManager : ViewGroupManager<NestedScrollableHost>(), RNCViewPa
                         ViewPager2.SCROLL_STATE_SETTLING -> "settling"
                         else -> throw IllegalStateException("Unsupported pageScrollState")
                     }
+                    // Emit a final onPageScroll with offset 0 when idle to clear
+                    // any residual floating-point offset from the scroll animation
+                    if (state == ViewPager2.SCROLL_STATE_IDLE) {
+                        UIManagerHelper.getEventDispatcherForReactTag(reactContext, host.id)?.dispatchEvent(
+                                PageScrollEvent(host.id, vp.currentItem, 0f)
+                        )
+                    }
                     UIManagerHelper.getEventDispatcherForReactTag(reactContext, host.id)?.dispatchEvent(
                             PageScrollStateChangedEvent(host.id, pageScrollState)
                     )

ios/PagerScrollDelegate.swift

@@ -33,6 +33,22 @@ class PagerScrollDelegate: NSObject, UIScrollViewDelegate, UICollectionViewDeleg
     delegate?.onPageScroll(data: eventData)
     originalDelegate?.scrollViewDidScroll?(scrollView)
   }
+
+  /// Emits a final onPageScroll with offset 0 before transitioning to idle,
+  /// clearing any residual floating-point offset from the scroll animation.
+  private func emitIdleWithCleanOffset(_ scrollView: UIScrollView) {
+    let isHorizontal = orientation == .horizontal
+    let pageSize = isHorizontal ? scrollView.frame.width : scrollView.frame.height
+    let contentOffset = isHorizontal ? scrollView.contentOffset.x : scrollView.contentOffset.y
+
+    if pageSize > 0 {
+      let page = Int(round(contentOffset / pageSize))
+      let eventData = OnPageScrollEventData(position: Double(page), offset: 0)
+      delegate?.onPageScroll(data: eventData)
+    }
+
+    delegate?.onPageScrollStateChanged(state: .idle)
+  }
 
   func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
     delegate?.onPageScrollStateChanged(state: .dragging)
@@ -45,18 +61,18 @@ class PagerScrollDelegate: NSObject, UIScrollViewDelegate, UICollectionViewDeleg
   }
 
   func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
-    delegate?.onPageScrollStateChanged(state: .idle)
+    emitIdleWithCleanOffset(scrollView)
     originalDelegate?.scrollViewDidEndDecelerating?(scrollView)
   }
-  
+
   func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
-    delegate?.onPageScrollStateChanged(state: .idle)
+    emitIdleWithCleanOffset(scrollView)
     originalDelegate?.scrollViewDidEndScrollingAnimation?(scrollView)
   }
-  
+
   func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
     if !decelerate {
-      delegate?.onPageScrollStateChanged(state: .idle)
+      emitIdleWithCleanOffset(scrollView)
     }
     originalDelegate?.scrollViewDidEndDragging?(scrollView, willDecelerate: decelerate)
   }