Fix for Try scrolling down and when new items are added the first item does not kept in the displayed list.

src/Controls/src/Core/Handlers/Items/Android/ItemsSources/ObservableItemsSource.cs

@@ -229,7 +229,7 @@ internal int ItemsCount()
 		internal object ElementAt(int index)
 		{
 			if (_itemsSource is IList list)
-				return list[index];
+				return (index >= 0 && index < list.Count) ? list[index] : null;
 
 			int count = 0;
 			foreach (var item in _itemsSource)
@@ -239,7 +239,7 @@ internal object ElementAt(int index)
 				count++;
 			}
 
-			return -1;
+			return null;
 		}
 	}
 }

src/Controls/src/Core/Handlers/Items/Android/MauiRecyclerView.cs

@@ -374,15 +374,8 @@ protected virtual void UpdateItemsUpdatingScrollMode()
 			if (ItemsViewAdapter == null || ItemsView == null)
 				return;
 
-			if (ItemsView.ItemsUpdatingScrollMode == ItemsUpdatingScrollMode.KeepItemsInView)
-			{
-				// Keeping the current items in view is the default, so we don't need to watch for data changes
-				_itemsUpdateScrollObserver.Stop(ItemsViewAdapter);
-			}
-			else
-			{
-				_itemsUpdateScrollObserver.Start(ItemsViewAdapter);
-			}
+			// We need to observe the adapter for changes for the ItemsUpdatingScrollMode.
+			_itemsUpdateScrollObserver.Start(ItemsViewAdapter);
 		}
 
 		public virtual void ScrollTo(ScrollToRequestEventArgs args)
@@ -392,6 +385,11 @@ public virtual void ScrollTo(ScrollToRequestEventArgs args)
 
 			var position = DetermineTargetPosition(args);
 
+			if (position < 0)
+			{
+				return;
+			}
+
 			if (args.IsAnimated)
 			{
 				ScrollHelper.AnimateScrollToPosition(position, args.ScrollToPosition);
@@ -598,6 +596,13 @@ internal void AdjustScrollForItemUpdate()
 			{
 				ScrollHelper.UndoNextScrollAdjustment();
 			}
+			else if (ItemsView.ItemsUpdatingScrollMode == ItemsUpdatingScrollMode.KeepItemsInView)
+			{
+				if (GetLayoutManager().ItemCount > 0)
+				{
+					ScrollTo(new ScrollToRequestEventArgs(0, 0, Microsoft.Maui.Controls.ScrollToPosition.Start, true));
+				}
+			}
 		}
 
 		GridLayoutManager CreateGridLayout(GridItemsLayout gridItemsLayout)

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

@@ -5,6 +5,7 @@
 using CoreGraphics;
 using Foundation;
 using Microsoft.Extensions.Logging;
+using Microsoft.Maui.Controls.Handlers.Items2;
 using UIKit;
 
 namespace Microsoft.Maui.Controls.Handlers.Items
@@ -500,6 +501,10 @@ public override void FinalizeCollectionViewUpdates()
 			{
 				ForceScrollToLastItem(CollectionView, _itemsLayout);
 			}
+			else if (ItemsUpdatingScrollMode == ItemsUpdatingScrollMode.KeepItemsInView)
+			{
+				ForceScrollToFirstItem(CollectionView, _itemsLayout);
+			}
 		}
 
 		void TrackOffsetAdjustment()
@@ -565,6 +570,33 @@ static bool UpdateWillShiftVisibleItems(UICollectionView collectionView, UIColle
 			return false;
 		}
 
+		static void ForceScrollToFirstItem(UICollectionView collectionView, ItemsLayout itemsLayout)
+		{
+			//CarouselView and CarouselView2 handle scrolling based on ItemsUpdatingScrollMode in CarouselViewController. Even when passing the 0th index, issues may arise in CarouselView since the position is determined by the center itemindex.
+			// Issue Link : https://github.com/dotnet/maui/issues/25991
+			if (collectionView.DataSource is CarouselViewController || collectionView.DataSource is CarouselViewController2)
+			{
+				return;
+			}
+
+			//Fix Added for ItemsUpdatingScrollMode.KeepItemsInView
+			int sections = (int)collectionView.NumberOfSections();
+
+			if (sections == 0)
+			{
+				return;
+			}
+
+			if (collectionView.NumberOfItemsInSection(0) > 0)
+			{
+				var indexPath = NSIndexPath.FromItemSection(0, 0);
+				if (itemsLayout.Orientation == ItemsLayoutOrientation.Vertical)
+					collectionView.ScrollToItem(indexPath, UICollectionViewScrollPosition.Top, true);
+				else
+					collectionView.ScrollToItem(indexPath, UICollectionViewScrollPosition.Right, true);
+			}
+		}
+
 		static void ForceScrollToLastItem(UICollectionView collectionView, ItemsLayout itemsLayout)
 		{
 			var sections = (int)collectionView.NumberOfSections();

src/Controls/tests/TestCases.HostApp/Issues/Issue26810.xaml

@@ -0,0 +1,65 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             xmlns:cv1="clr-namespace:Maui.Controls.Sample"
+             x:Class="Maui.Controls.Sample.Issues.Issue26810">
+        <Grid RowDefinitions="50,50,50,*"
+              AutomationId="26810MainGrid">
+                <Grid Grid.Row="0"
+                      ColumnDefinitions="*,*,*">
+                        <Button Text="KeepItemsInView"
+                                AutomationId="26810FirstItemButton"
+                                x:Name="KeepItemsInView"
+                                Grid.Column="0"
+                                Clicked="ItemsUpdatingScrollMode_Clicked"
+                                HorizontalOptions="Center"
+                                VerticalOptions="Center"/>
+                        <Button Text="KeepScrollOffset"
+                                AutomationId="26810ScrollOffsetButton"
+                                x:Name="KeepScrollOffset"
+                                Grid.Column="1"
+                                Clicked="ItemsUpdatingScrollMode_Clicked"
+                                HorizontalOptions="Center"
+                                VerticalOptions="Center"/>
+                        <Button Text="KeepLastItemInView"
+                                AutomationId="26810LastItemButton"
+                                x:Name="KeepLastItemInView"
+                                Grid.Column="2"
+                                Clicked="ItemsUpdatingScrollMode_Clicked"
+                                HorizontalOptions="Center"
+                                VerticalOptions="Center"/>
+                </Grid>
+                <Button Text="Scroll to Random Item"
+                        AutomationId="26810Button"
+                        x:Name="ScrollToButton"
+                        Grid.Row="1"
+                        Clicked="ScrollToButton_Clicked"
+                        HorizontalOptions="Center"
+                        VerticalOptions="Center"/>
+                <Button Text="Add New Item"
+                        AutomationId="26810AddButton"
+                        x:Name="AddButton"
+                        Grid.Row="2"
+                        Clicked="AddButton_Clicked"
+                        HorizontalOptions="Center"
+                        VerticalOptions="Center"/>
+                <cv1:CollectionView1 x:Name="CollectionView"
+                                     AutomationId="26810CollectionView"
+                                     Grid.Row="3">
+                        <cv1:CollectionView1.ItemsLayout>
+                                <LinearItemsLayout ItemSpacing="5"
+                                                   Orientation="Horizontal"/>
+                        </cv1:CollectionView1.ItemsLayout>
+                        <cv1:CollectionView1.ItemTemplate>
+                                <DataTemplate>
+                                        <Grid HeightRequest="50">
+                                                <Label Text="{Binding Name}"
+                                                       AutomationId="{Binding AutomationId}"
+                                                       VerticalOptions="Center"
+                                                       HorizontalOptions="Center"/>
+                                        </Grid>
+                                </DataTemplate>
+                        </cv1:CollectionView1.ItemTemplate>
+                </cv1:CollectionView1>
+        </Grid>
+</ContentPage>

src/Controls/tests/TestCases.HostApp/Issues/Issue26810.xaml.cs

@@ -0,0 +1,51 @@
+using System.Collections.ObjectModel;
+
+namespace Maui.Controls.Sample.Issues;
+[Issue(IssueTracker.Github, 26810, "Scroll To first item in CollectionView when updating the collection with KeepItemsInView",
+		PlatformAffected.Android)]
+public partial class Issue26810 : ContentPage
+{
+	private ObservableCollection<Issue26810ItemModel> Items { get; set; } = new ObservableCollection<Issue26810ItemModel>();
+	public Issue26810()
+	{
+		InitializeComponent();
+		for (int i = 1; i <= 30; i++)
+		{
+			Items.Add(new Issue26810ItemModel { Name = $"Preloaded Item {i}", AutomationId = $"Item{i}" });
+		}
+		CollectionView.ItemsSource = Items;
+		this.BindingContext = this;
+	}
+
+	private void ItemsUpdatingScrollMode_Clicked(object sender, EventArgs e)
+	{
+		var button = (Button)sender;
+		if (button.Text == "KeepScrollOffset")
+		{
+			CollectionView.ItemsUpdatingScrollMode = ItemsUpdatingScrollMode.KeepScrollOffset;
+		}
+		else if (button.Text == "KeepLastItemInView")
+		{
+			CollectionView.ItemsUpdatingScrollMode = ItemsUpdatingScrollMode.KeepLastItemInView;
+		}
+	}
+
+	private void AddButton_Clicked(object sender, EventArgs e)
+	{
+		Items.Add(new Issue26810ItemModel { Name = $"Item {Items.Count + 1}", AutomationId = $"Item{Items.Count + 1}" });
+	}
+	private void ScrollToButton_Clicked(object sender, EventArgs e)
+	{
+		if (Items.Count > 0)
+		{
+			// Scroll to random item
+			CollectionView.ScrollTo(19, position: ScrollToPosition.End, animate: true);
+		}
+	}
+}
+
+public class Issue26810ItemModel
+{
+	public string Name { get; set; }
+	public string AutomationId { get; set; }
+}

src/Controls/tests/TestCases.HostApp/Issues/Issue26810Vertical.xaml

@@ -0,0 +1,61 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             xmlns:cv1="clr-namespace:Maui.Controls.Sample"
+             x:Class="Maui.Controls.Sample.Issues.Issue26810Vertical">
+    <Grid RowDefinitions="50,50,50,*"
+          AutomationId="26810MainGrid">
+        <Grid Grid.Row="0"
+              ColumnDefinitions="*,*,*">
+            <Button Text="KeepItemsInView"
+                    AutomationId="26810FirstItemButton"
+                    x:Name="KeepItemsInView"
+                    Grid.Column="0"
+                    Clicked="ItemsUpdatingScrollMode_Clicked"
+                    HorizontalOptions="Center"
+                    VerticalOptions="Center"/>
+            <Button Text="KeepScrollOffset"
+                    AutomationId="26810ScrollOffsetButton"
+                    x:Name="KeepScrollOffset"
+                    Grid.Column="1"
+                    Clicked="ItemsUpdatingScrollMode_Clicked"
+                    HorizontalOptions="Center"
+                    VerticalOptions="Center"/>
+            <Button Text="KeepLastItemInView"
+                    AutomationId="26810LastItemButton"
+                    x:Name="KeepLastItemInView"
+                    Grid.Column="2"
+                    Clicked="ItemsUpdatingScrollMode_Clicked"
+                    HorizontalOptions="Center"
+                    VerticalOptions="Center"/>
+        </Grid>
+        <Button Text="Scroll to Random Item"
+                AutomationId="26810Button"
+                x:Name="ScrollToButton"
+                Grid.Row="1"
+                Clicked="ScrollToButton_Clicked"
+                HorizontalOptions="Center"
+                VerticalOptions="Center"/>
+        <Button Text="Add New Item"
+                AutomationId="26810AddButton"
+                x:Name="AddButton"
+                Grid.Row="2"
+                Clicked="AddButton_Clicked"
+                HorizontalOptions="Center"
+                VerticalOptions="Center"/>
+        <cv1:CollectionView1 x:Name="CollectionView"
+                             AutomationId="26810CollectionView"
+                             Grid.Row="3">
+            <cv1:CollectionView1.ItemTemplate>
+                <DataTemplate>
+                    <Grid HeightRequest="50">
+                        <Label Text="{Binding Name}"
+                               AutomationId="{Binding AutomationId}"
+                               VerticalOptions="Center"
+                               HorizontalOptions="Center"/>
+                    </Grid>
+                </DataTemplate>
+            </cv1:CollectionView1.ItemTemplate>
+        </cv1:CollectionView1>
+    </Grid>
+</ContentPage>

src/Controls/tests/TestCases.HostApp/Issues/Issue26810Vertical.xaml.cs

@@ -0,0 +1,47 @@
+using System.Collections.ObjectModel;
+
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.None, 26810, "Scroll To first item in CollectionView with vertical orientation when updating the collection with KeepItemsInView",
+		PlatformAffected.Android)]
+
+public partial class Issue26810Vertical : ContentPage
+{
+
+	private ObservableCollection<Issue26810ItemModel> Items { get; set; } = new ObservableCollection<Issue26810ItemModel>();
+	public Issue26810Vertical()
+	{
+		InitializeComponent();
+		for (int i = 1; i <= 30; i++)
+		{
+			Items.Add(new Issue26810ItemModel { Name = $"Preloaded Item {i}", AutomationId = $"Item{i}" });
+		}
+		CollectionView.ItemsSource = Items;
+		this.BindingContext = this;
+	}
+	private void ItemsUpdatingScrollMode_Clicked(object sender, EventArgs e)
+	{
+		var button = (Button)sender;
+		if (button.Text == "KeepScrollOffset")
+		{
+			CollectionView.ItemsUpdatingScrollMode = ItemsUpdatingScrollMode.KeepScrollOffset;
+		}
+		else if (button.Text == "KeepLastItemInView")
+		{
+			CollectionView.ItemsUpdatingScrollMode = ItemsUpdatingScrollMode.KeepLastItemInView;
+		}
+	}
+
+	private void AddButton_Clicked(object sender, EventArgs e)
+	{
+		Items.Add(new Issue26810ItemModel { Name = $"Item {Items.Count + 1}", AutomationId = $"Item{Items.Count + 1}" });
+	}
+	private void ScrollToButton_Clicked(object sender, EventArgs e)
+	{
+		if (Items.Count > 0)
+		{
+			// Scroll to random item
+			CollectionView.ScrollTo(19, position: ScrollToPosition.End, animate: true);
+		}
+	}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/CollectionViewUITests.CollectionViewItemsUpdatingScrollMode.cs

@@ -15,7 +15,6 @@ public CollectionViewItemsUpdatingScrollModeUITests(TestDevice device)
 
 		protected override bool ResetAfterEachTest => true;
 
-#if TEST_FAILS_ON_WINDOWS // For more information, see :https://github.com/dotnet/maui/issues/28006
 		// KeepScrollOffset (src\Compatibility\ControlGallery\src\Issues.Shared\CollectionViewItemsUpdatingScrollMode.cs)
 		[Test]
 		[Category(UITestCategories.CollectionView)]
@@ -30,9 +29,9 @@ public void KeepItemsInView()
 				App.Click("AddItemAbove");
 			}
 
-			App.WaitForElement("Vegetables.jpg, 10");
+			App.WaitForNoElement("Vegetables.jpg, 10");
 		}
-#endif
+
 
 #if TEST_FAILS_ON_IOS && TEST_FAILS_ON_CATALYST // The test fails on iOS and macOS because Appium is unable to locate the Picker control elements resulting in a TimeoutException. For more information, see: https://github.com/dotnet/maui/issues/28024
 		// KeepScrollOffset (src\Compatibility\ControlGallery\src\Issues.Shared\CollectionViewItemsUpdatingScrollMode.cs)