[iOS] Fix for the CollectionView to prevent duplicate groups or crash…

…es when adding a new item to a group or when adding a new group. (#24873)

* [iOS] CollectionView issue fix.

* Added test case.

* Added snapshots.

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

@@ -173,17 +173,9 @@ internal CGSize GetReferenceSizeForheaderOrFooter(UICollectionView collectionVie
 				return CGSize.Empty;
 			}
 
-			if (!(OperatingSystem.IsIOSVersionAtLeast(11) || OperatingSystem.IsTvOSVersionAtLeast(11)))
-			{
-				// iOS 10 crashes if we try to dequeue a cell for measurement
-				// so we'll use an alternate method
-				return MeasureSupplementaryView(elementKind, section);
-			}
-
-			var cell = GetViewForSupplementaryElement(collectionView, elementKind,
-				NSIndexPath.FromItemSection(0, section)) as ItemsViewCell;
-
-			return cell.Measure();
+			// Dequeuing a supplementary view for measurement caused multiple instances of the header/footer to appear in the view.
+			// We now always use MeasureSupplementaryView, an alternate approach for calculating the size without dequeuing the view.
+			return MeasureSupplementaryView(elementKind, section);
 		}
 
 		internal void SetScrollAnimationEndedCallback(Action callback)

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

@@ -204,7 +204,7 @@ bool NotLoadedYet()
 
 		void Add(NotifyCollectionChangedEventArgs args)
 		{
-			if (ReloadRequired())
+			if (NotLoadedYet())
 			{
 				Reload();
 				return;

src/Controls/tests/TestCases.HostApp/Issues/Issue17969.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.Issue17969"
+             xmlns:ns="clr-namespace:Maui.Controls.Sample.Issues"
+             x:DataType="ns:GroupedCollectionViewModel">
+
+  <Grid RowDefinitions="Auto,*">
+    <HorizontalStackLayout Grid.Row="0">
+      <Button Text="Add New Item" Clicked="OnAddClicked" AutomationId="addItem"/>
+      <Button Text="Add New Group" Clicked="OnResetClicked" AutomationId="addGroup"/>
+    </HorizontalStackLayout>
+    <CollectionView ItemsSource="{Binding Animals}" 
+                    AutomationId="collectionView" 
+                    Grid.Row="1"
+                    IsGrouped="true">
+      <CollectionView.ItemTemplate>
+        <DataTemplate x:DataType="ns:Animal">
+          <Grid Padding="10">
+            <Label Text="{Binding Name}" />
+          </Grid>
+        </DataTemplate>
+      </CollectionView.ItemTemplate>
+      <CollectionView.GroupHeaderTemplate>
+        <DataTemplate x:DataType="ns:AnimalGroup">
+          <Label Text="{Binding Name}" FontSize="18" FontAttributes="Bold"/>
+        </DataTemplate>
+      </CollectionView.GroupHeaderTemplate>
+      <CollectionView.GroupFooterTemplate>
+        <DataTemplate x:DataType="ns:AnimalGroup">
+          <Label Text="{Binding Count, StringFormat='Count: {0:D}'}"
+              Margin="0,0,0,10" />
+        </DataTemplate>
+      </CollectionView.GroupFooterTemplate>
+    </CollectionView>
+  </Grid>
+</ContentPage>

src/Controls/tests/TestCases.HostApp/Issues/Issue17969.xaml.cs

@@ -0,0 +1,187 @@
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using Microsoft.Maui.Controls;
+
+namespace Maui.Controls.Sample.Issues
+{
+
+	[Issue(IssueTracker.Github, 17969, "CollectionView duplicates group headers/footers when adding a new item to a group or crashes when adding a new group with empty view", PlatformAffected.iOS)]
+	public partial class Issue17969 : ContentPage
+	{
+		GroupedCollectionViewModel viewModel;
+		public Issue17969()
+		{
+			InitializeComponent();
+			viewModel = new GroupedCollectionViewModel();
+			BindingContext = viewModel;
+		}
+
+		private void OnAddClicked(object sender, EventArgs e)
+		{
+			viewModel.AddAnimal();
+		}
+
+		private void OnResetClicked(object sender, EventArgs e)
+		{
+			viewModel.Reset();
+		}
+
+	}
+
+	public class TestItem
+	{
+		public string Name { get; set; }
+	}
+	public class Animal
+	{
+		public string Name { get; set; }
+	}
+
+	public class AnimalGroup : ObservableCollection<Animal>
+	{
+		public string Name { get; private set; }
+
+		public AnimalGroup(string name, List<Animal> animals) : base(animals)
+		{
+			Name = name;
+		}
+	}
+
+	public class GroupedCollectionViewModel
+	{
+		public GroupedCollectionViewModel()
+		{
+			Init();
+
+		}
+
+		private void Init()
+		{
+			AnimalBaseList.Clear();
+			AnimalBaseList.Add(new AnimalGroup("Bears", new List<Animal>
+			{
+				new Animal
+				{
+					Name = "American Black Bear",
+				},
+				new Animal
+				{
+					Name = "Asian Black Bear",
+				},
+				new Animal
+				{
+					Name = "Brown Bear",
+				},
+				new Animal
+				{
+					Name = "Grizzly-Polar Bear Hybrid",
+				},
+				new Animal
+				{
+					Name = "Sloth Bear",
+				},
+				new Animal
+				{
+					Name = "Sun Bear",
+				},
+				new Animal
+				{
+					Name = "Polar Bear",
+				},
+				new Animal
+				{
+					Name = "Spectacled Bear",
+				},
+				new Animal
+				{
+					Name = "Short-faced Bear",
+				},
+				new Animal
+				{
+					Name = "California Grizzly Bear",
+				}
+			}));
+
+			AnimalBaseList.Add(new AnimalGroup("Cats", new List<Animal>
+			{
+				new Animal
+				{
+					Name = "Abyssinian",
+				},
+				new Animal
+				{
+					Name = "Arabian Mau",
+				},
+				new Animal
+				{
+					Name = "Bengal",
+				},
+				new Animal
+				{
+					Name = "Burmese",
+				},
+				new Animal
+				{
+					Name = "Cyprus",
+				},
+				new Animal
+				{
+					Name = "German Rex",
+				},
+				new Animal
+				{
+					Name = "Highlander",
+				},
+				new Animal
+				{
+					Name = "Peterbald",
+				},
+				new Animal
+				{
+					Name = "Scottish Fold",
+				},
+				new Animal
+				{
+					Name = "Sphynx",
+				}
+			}));
+
+			Animals.Add(new AnimalGroup(AnimalBaseList[0].Name, new List<Animal>()));
+
+			AddAnimal();
+
+			Animals.Add(new AnimalGroup(AnimalBaseList[1].Name, AnimalBaseList[1].ToList()));
+
+		}
+
+
+		public bool AddAnimal()
+		{
+			// Add animal from first group
+			var sourceGroup = AnimalBaseList.First();
+			var targetGroup = Animals.First();
+
+			if (sourceGroup.Count == 0)
+				return false;
+
+			var animal = sourceGroup.First();
+			targetGroup.Add(animal);
+			sourceGroup.Remove(animal);
+
+			return true;
+		}
+
+		public void Reset()
+		{
+			Animals.Clear();
+			Init();
+
+		}
+
+		private List<AnimalGroup> AnimalBaseList { get; set; } = new List<AnimalGroup>();
+
+		public ObservableCollection<AnimalGroup> Animals { get; private set; } = new ObservableCollection<AnimalGroup>();
+	}
+
+}

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue17969.cs

@@ -0,0 +1,39 @@
+#if !MACCATALYST
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues
+{
+	public class Issue17969 : _IssuesUITest
+	{
+
+		public Issue17969(TestDevice device)
+		: base(device)
+		{ }
+
+		public override string Issue => "CollectionView duplicates group headers/footers when adding a new item to a group or crashes when adding a new group with empty view";
+
+		[Test]
+		[Category(UITestCategories.CollectionView)]
+		[FailsOnWindows]
+		public void CollectionViewDuplicateViewsWhenAddItemToGroup()
+		{
+			App.WaitForElement("collectionView");
+			App.Tap("addItem");
+			VerifyScreenshot();
+
+		}
+
+		[Test]
+		[Category(UITestCategories.CollectionView)]
+		[FailsOnWindows]
+		public void CollectionViewAddGroupWhenViewIsEmpty()
+		{
+			App.WaitForElement("collectionView");
+			App.Tap("addGroup");
+			VerifyScreenshot();
+		}
+	}
+}
+#endif