[Windows] Fix crash using ScrollTo on CollectionView (dotnet#19921)

* Fix 17865

* Added device test

* Updated test

* Fixup use of event

* Update MauiProgram.cs

* Fix UI test

---------

Co-authored-by: Mike Corsaro <[email protected]>
Co-authored-by: Mike Corsaro <[email protected]>
Co-authored-by: Gerald Versluis <[email protected]>

src/Controls/src/Core/Platform/Windows/CollectionView/ScrollHelpers.cs

@@ -187,6 +187,13 @@ static async Task<UWPPoint> GetApproximateTargetAsync(ListViewBase list, ScrollV
 		internal static void JumpToIndexAsync(ListViewBase list, int index, ScrollToPosition scrollToPosition)
 		{
 			var scrollViewer = list.GetFirstDescendant<ScrollViewer>();
+
+			if (scrollViewer is null)
+			{
+				// If ScrollViewer is not found, do nothing.
+				return;
+			}
+
 			var con = list.ContainerFromIndex(index);
 			if (con is UIElement uIElement)
 			{
@@ -201,8 +208,25 @@ internal static void JumpToIndexAsync(ListViewBase list, int index, ScrollToPosi
 
 		public static async Task JumpToItemAsync(ListViewBase list, object targetItem, ScrollToPosition scrollToPosition)
 		{
+			if(!list.IsLoaded)
+			{
+				list.OnLoaded(async () =>
+				{
+					// If the ListView is not loaded, wait for it to load and reinvoke the JumpToItem.
+					await JumpToItemAsync(list, targetItem, scrollToPosition);
+				});
+
+				return;
+			}
+
 			var scrollViewer = list.GetFirstDescendant<ScrollViewer>();
 
+			if (scrollViewer is null)
+			{
+				// If ScrollViewer is not found, do nothing.
+				return;
+			}
+
 			var tcs = new TaskCompletionSource<object>();
 			Func<Task> adjust = null;
 
@@ -271,6 +295,17 @@ static async Task<bool> ScrollToItemAsync(ListViewBase list, object targetItem,
 
 		public static async Task AnimateToItemAsync(ListViewBase list, object targetItem, ScrollToPosition scrollToPosition)
 		{
+			if (!list.IsLoaded)
+			{
+				list.OnLoaded(async () =>
+				{
+					// If the ListView is not loaded, wait for it to load and reinvoke the AnimateToItem.
+					await AnimateToItemAsync(list, targetItem, scrollToPosition);
+				});
+
+				return;
+			}
+
 			var scrollViewer = list.GetFirstDescendant<ScrollViewer>();
 
 			if (scrollViewer == null)

src/Controls/tests/TestCases.HostApp/Issues/Issue17865.xaml

@@ -0,0 +1,37 @@
+<?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"
+             x:Class="Maui.Controls.Sample.Issues.Issue17865"
+             xmlns:ns="clr-namespace:Maui.Controls.Sample.Issues"
+             Title="Issue 17865">
+    <Grid>
+        <Grid.RowDefinitions>
+            <RowDefinition 
+                Height="Auto"/>
+            <RowDefinition
+                Height="*"/>
+        </Grid.RowDefinitions>
+        <HorizontalStackLayout
+            Padding="5">
+            <Button 
+                AutomationId="WaitForStubControl"
+                Text="Reveal Last Item" 
+                Clicked="OnButtonClicked"/>
+        </HorizontalStackLayout>
+        <CollectionView 
+            x:Name="collectionView"
+            Grid.Row="1" 
+            ItemsSource="{Binding Items}">
+            <CollectionView.ItemTemplate>
+                <DataTemplate>
+                    <Label
+                        Margin="5,2" 
+                        Text="{Binding ItemText}"
+                        HorizontalOptions="Fill"
+                        TextColor="Gray"/>
+                </DataTemplate>
+            </CollectionView.ItemTemplate>
+        </CollectionView>
+    </Grid>
+
+</ContentPage>

src/Controls/tests/TestCases.HostApp/Issues/Issue17865.xaml.cs

@@ -0,0 +1,71 @@
+using System;
+using System.Collections.ObjectModel;
+using System.Linq;
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.Xaml;
+
+namespace Maui.Controls.Sample.Issues
+{
+	internal class Issue17865Model
+	{
+		public Issue17865Model(int itemIndex)
+		{
+			ItemText = $"Item #{itemIndex}";
+		}
+
+		public string ItemText { get; }
+
+	}
+
+	internal class Issue17865ViewModel : BindableObject
+	{
+		ObservableCollection<Issue17865Model> items = new();
+
+		public Issue17865ViewModel()
+		{
+			Populate();
+		}
+
+		void Populate()
+		{
+			for (int i = 0; i < 100; i++)
+			{
+				items.Add(new Issue17865Model(i));
+			}
+		}
+
+		public ObservableCollection<Issue17865Model> Items => items;
+	}
+
+	[XamlCompilation(XamlCompilationOptions.Compile)]
+	[Issue(IssueTracker.Github, 17865, "CollectionView throws NRE when ScrollTo method is called from a handler of event Window.Created", PlatformAffected.UWP)]
+	public partial class Issue17865 : ContentPage
+	{
+		readonly Issue17865ViewModel _viewModel;
+
+		public Issue17865()
+		{
+			InitializeComponent();
+
+			collectionView.Loaded += CollectionView_Loaded;
+
+			BindingContext = _viewModel = new Issue17865ViewModel();
+		}
+
+		private void CollectionView_Loaded(object sender, EventArgs e)
+		{
+			RevealLastItem();
+		}
+
+		public void RevealLastItem()
+		{
+			var item = _viewModel.Items.Last();
+			collectionView.ScrollTo(item, null, ScrollToPosition.MakeVisible, false);
+		}
+
+		private void OnButtonClicked(object sender, EventArgs e)
+		{
+			RevealLastItem();
+		}
+	}
+}

src/Controls/tests/TestCases.HostApp/MauiProgram.cs

@@ -96,4 +96,4 @@ protected override Window CreateWindow(IActivationState activationState)
 		}
 #endif
 	}
-}
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue17865.cs

@@ -0,0 +1,28 @@
+#if WINDOWS
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues
+{
+	public class Issue17865 : _IssuesUITest
+	{
+		const string ButtonId = "WaitForStubControl";
+
+		public Issue17865(TestDevice device) : base(device) { }
+
+		public override string Issue => "CollectionView throws NRE when ScrollTo method is called from a handler of event Window.Created";
+
+		[Test]
+		[Category(UITestCategories.CollectionView)]
+		public void Issue17865Test()
+		{
+			App.WaitForElement(ButtonId);
+
+			App.Click(ButtonId);
+
+			// NOTE: Without crashes the test has passed.
+		}
+	}
+}
+#endif