[iOS] Fix incorrect FirstVisibleItemIndex reported by CollectionView.Scrolled after programmatic scroll

src/Controls/src/Core/Handlers/Items/iOS/ItemsViewDelegator.cs

@@ -1,5 +1,6 @@
 #nullable disable
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using CoreGraphics;
 using Foundation;
@@ -124,7 +125,7 @@ protected virtual (bool VisibleItems, NSIndexPath First, NSIndexPath Center, NSI
 
 			if (visibleItems)
 			{
-				firstVisibleItemIndex = indexPathsForVisibleItems.First();
+				firstVisibleItemIndex = GetFirstVisibleIndexPathUsingLayoutAttributes(collectionView, indexPathsForVisibleItems);
 				centerItemIndex = GetCenteredIndexPath(collectionView);
 				lastVisibleItemIndex = indexPathsForVisibleItems.Last();
 			}
@@ -162,6 +163,48 @@ static int GetItemIndex(NSIndexPath indexPath, IItemsViewSource itemSource)
 			return index;
 		}
 
+		static NSIndexPath GetFirstVisibleIndexPathUsingLayoutAttributes(UICollectionView collectionView, IEnumerable<NSIndexPath> indexPathsForVisibleItems)
+		{
+			if (!indexPathsForVisibleItems.Any())
+				return null;
+
+			var layout = collectionView.CollectionViewLayout;
+			if (layout is null)
+				return indexPathsForVisibleItems.First();
+
+			var visibleRect = new CGRect(collectionView.ContentOffset, collectionView.Bounds.Size);
+			var layoutAttributes = layout.LayoutAttributesForElementsInRect(visibleRect);
+			if (layoutAttributes is null || layoutAttributes.Length == 0)
+				return indexPathsForVisibleItems.First();
+
+			var flowLayout = layout as UICollectionViewFlowLayout;
+			bool isVertical = flowLayout?.ScrollDirection != UICollectionViewScrollDirection.Horizontal;
+			// Find the first visible cell (not headers/footers) based on scroll direction
+			NSIndexPath firstVisibleIndexPath = null;
+			nfloat minPosition = nfloat.MaxValue;
+
+			for (int i = 0; i < layoutAttributes.Length; i++)
+			{
+				var attr = layoutAttributes[i];
+				// Skip non-cell elements (headers, footers, decorations)
+				if (attr.RepresentedElementCategory != UICollectionElementCategory.Cell)
+					continue;
+
+				// Skip items that don't intersect with visible rect
+				if (!attr.Frame.IntersectsWith(visibleRect))
+					continue;
+
+				nfloat position = isVertical ? attr.Frame.Y : attr.Frame.X;
+				if (position < minPosition)
+				{
+					minPosition = position;
+					firstVisibleIndexPath = attr.IndexPath;
+				}
+			}
+
+			return firstVisibleIndexPath ?? indexPathsForVisibleItems.First();
+		}
+
 		static NSIndexPath GetCenteredIndexPath(UICollectionView collectionView)
 		{
 			NSIndexPath centerItemIndex = null;

src/Controls/src/Core/Handlers/Items2/iOS/ItemsViewDelegator2.cs

@@ -1,5 +1,6 @@
 #nullable disable
 using System;
+using System.Collections.Generic;
 using System.Linq;
 using CoreGraphics;
 using Foundation;
@@ -125,7 +126,7 @@ protected virtual (bool VisibleItems, NSIndexPath First, NSIndexPath Center, NSI
 
 			if (visibleItems)
 			{
-				firstVisibleItemIndex = indexPathsForVisibleItems.First();
+				firstVisibleItemIndex = GetFirstVisibleIndexPathUsingLayoutAttributes(collectionView, indexPathsForVisibleItems);
 				centerItemIndex = GetCenteredIndexPath(collectionView);
 				lastVisibleItemIndex = indexPathsForVisibleItems.Last();
 			}
@@ -163,6 +164,48 @@ static int GetItemIndex(NSIndexPath indexPath, IItemsViewSource itemSource)
 			return index;
 		}
 
+		static NSIndexPath GetFirstVisibleIndexPathUsingLayoutAttributes(UICollectionView collectionView, IEnumerable<NSIndexPath> indexPathsForVisibleItems)
+		{
+			if (!indexPathsForVisibleItems.Any())
+				return null;
+
+			var layout = collectionView.CollectionViewLayout;
+			if (layout is null)
+				return indexPathsForVisibleItems.First();
+
+			var visibleRect = new CGRect(collectionView.ContentOffset, collectionView.Bounds.Size);
+			var layoutAttributes = layout.LayoutAttributesForElementsInRect(visibleRect);
+			if (layoutAttributes is null || layoutAttributes.Length == 0)
+				return indexPathsForVisibleItems.First();
+
+			var flowLayout = layout as UICollectionViewFlowLayout;
+			bool isVertical = flowLayout?.ScrollDirection != UICollectionViewScrollDirection.Horizontal;
+			// Find the first visible cell (not headers/footers) based on scroll direction
+			NSIndexPath firstVisibleIndexPath = null;
+			nfloat minPosition = nfloat.MaxValue;
+
+			for (int i = 0; i < layoutAttributes.Length; i++)
+			{
+				var attr = layoutAttributes[i];
+				// Skip non-cell elements (headers, footers, decorations)
+				if (attr.RepresentedElementCategory != UICollectionElementCategory.Cell)
+					continue;
+
+				// Skip items that don't intersect with visible rect
+				if (!attr.Frame.IntersectsWith(visibleRect))
+					continue;
+
+				nfloat position = isVertical ? attr.Frame.Y : attr.Frame.X;
+				if (position < minPosition)
+				{
+					minPosition = position;
+					firstVisibleIndexPath = attr.IndexPath;
+				}
+			}
+
+			return firstVisibleIndexPath ?? indexPathsForVisibleItems.First();
+		}
+
 		static NSIndexPath GetCenteredIndexPath(UICollectionView collectionView)
 		{
 			NSIndexPath centerItemIndex = null;

src/Controls/tests/TestCases.HostApp/Issues/Issue33614.cs

@@ -0,0 +1,76 @@
+using System.Collections.ObjectModel;
+
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 33614, "CollectionView Scrolled event reports incorrect FirstVisibleItemIndex after programmatic ScrollTo", PlatformAffected.iOS | PlatformAffected.macOS)]
+public class Issue33614 : ContentPage
+{
+    public ObservableCollection<string> Items { get; set; }
+    private Label _firstIndexLabel;
+    private CollectionView2 _collectionView;
+    public Issue33614()
+    {
+        Items = new ObservableCollection<string>();
+        for (int i = 0; i <= 50; i++)
+        {
+            Items.Add($"Item_{i}");
+        }
+
+        _firstIndexLabel = new Label
+        {
+            AutomationId = "FirstIndexLabel",
+            Text = "FirstVisibleItemIndex: 0",
+            IsVisible = false,
+        };
+
+        var scrollToButton = new Button
+        {
+            AutomationId = "ScrollToButton",
+            Text = "ScrollTo Index 15",
+            WidthRequest = 150
+        };
+        scrollToButton.Clicked += OnScrollToButtonClicked;
+
+        _collectionView = new CollectionView2
+        {
+            AutomationId = "TestCollectionView",
+            ItemsSource = Items,
+            HeightRequest = 600,
+            ItemTemplate = new DataTemplate(() =>
+            {
+                var label = new Label();
+                label.SetBinding(Label.TextProperty, ".");
+                return new Border
+                {
+                    Margin = new Thickness(5),
+                    Padding = new Thickness(10),
+                    Stroke = Colors.Gray,
+                    Content = label
+                };
+            })
+        };
+
+        _collectionView.Scrolled += OnCollectionViewScrolled;
+
+        Content = new StackLayout
+        {
+            Children =
+            {
+                _firstIndexLabel,
+                 scrollToButton,
+                _collectionView
+            }
+        };
+    }
+
+    private void OnCollectionViewScrolled(object sender, ItemsViewScrolledEventArgs e)
+    {
+        _firstIndexLabel.Text = $"FirstVisibleItemIndex: {e.FirstVisibleItemIndex}";
+        _firstIndexLabel.IsVisible = true;
+    }
+
+    private void OnScrollToButtonClicked(object sender, EventArgs e)
+    {
+        _collectionView.ScrollTo(15, position: ScrollToPosition.Start, animate: true);
+    }
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue33614.cs

@@ -0,0 +1,22 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue33614 : _IssuesUITest
+{
+    public override string Issue => "CollectionView Scrolled event reports incorrect FirstVisibleItemIndex after programmatic ScrollTo";
+
+    public Issue33614(TestDevice device) : base(device) { }
+
+    [Test]
+    [Category(UITestCategories.CollectionView)]
+    public void FirstVisibleItemIndexShouldBeCorrectAfterScrollTo()
+    {
+        App.WaitForElement("ScrollToButton");
+        App.Tap("ScrollToButton");
+        var firstIndexText = App.FindElement("FirstIndexLabel").GetText();
+        Assert.That(firstIndexText, Is.EqualTo("FirstVisibleItemIndex: 15"));
+    }
+}