[Android] CollectionView: Fix drag-and-drop reordering into empty groups

src/Controls/src/Core/Handlers/Items/Android/Adapters/ReorderableItemsViewAdapter.cs

@@ -47,6 +47,16 @@ public bool OnItemMove(int fromPosition, int toPosition)
 					return false;
 				}
 
+				if (fromItemIndex < 0 || fromItemIndex >= fromList.Count)
+				{
+					return false;
+				}
+
+				if (toItemIndex < 0 || toItemIndex > toList.Count)
+				{
+					return false;
+				}
+
 				if (fromList != null && toList != null)
 				{
 					var fromItem = fromList[fromItemIndex];

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

@@ -28,7 +28,10 @@ public override int GetMovementFlags(RecyclerView recyclerView, RecyclerView.Vie
 
 		public override bool OnMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target)
 		{
-			if (viewHolder.ItemViewType != target.ItemViewType)
+			var sourceItemViewType = viewHolder.ItemViewType;
+
+			if (sourceItemViewType == ItemViewType.Header || sourceItemViewType == ItemViewType.Footer
+				|| sourceItemViewType == ItemViewType.GroupHeader || sourceItemViewType == ItemViewType.GroupFooter)
 			{
 				return false;
 			}

src/Controls/tests/TestCases.HostApp/Issues/Issue12008.cs

@@ -0,0 +1,225 @@
+using System.Collections.ObjectModel;
+using System.ComponentModel;
+
+namespace Maui.Controls.Sample.Issues;
+
+[Issue(IssueTracker.Github, 12008, "CollectionView Drag and Drop Reordering Can't Drop in Empty Group", PlatformAffected.Android | PlatformAffected.iOS | PlatformAffected.macOS)]
+public partial class Issue12008 : ContentPage
+{
+	private Label statusLabel;
+	private CollectionView collectionView;
+	private Button btnCreateEmptyGroup;
+	public Issue12008()
+	{
+		this.BindingContext = new Issue12008ViewModel();
+		var grid = new Grid
+		{
+			RowDefinitions = new RowDefinitionCollection
+			{
+				new RowDefinition { Height = GridLength.Auto },
+				new RowDefinition { Height = GridLength.Star }
+			}
+		};
+
+		// Top StackLayout
+		var stackLayout = new StackLayout
+		{
+			Padding = 10
+		};
+
+		var titleLabel = new Label
+		{
+			Text = "Drag and Drop Test - Empty Groups",
+			FontSize = 18,
+			FontAttributes = FontAttributes.Bold,
+			Margin = new Thickness(0, 0, 0, 10)
+		};
+
+		var instructionsLabel = new Label
+		{
+			Text = "Instructions: Try dragging items between groups, including into empty groups.",
+			FontSize = 14,
+			Margin = new Thickness(0, 0, 0, 10)
+		};
+
+		btnCreateEmptyGroup = new Button
+		{
+			Text = "Create Empty Group",
+			AutomationId = "CreateEmptyGroupButton12008"
+		};
+		btnCreateEmptyGroup.Clicked += OnCreateEmptyGroupClicked;
+
+		statusLabel = new Label
+		{
+			Text = "Status: Ready",
+			FontSize = 12,
+			AutomationId = "StatusLabel12008"
+		};
+
+		stackLayout.Children.Add(titleLabel);
+		stackLayout.Children.Add(instructionsLabel);
+		stackLayout.Children.Add(btnCreateEmptyGroup);
+		stackLayout.Children.Add(statusLabel);
+
+		Grid.SetRow(stackLayout, 0);
+		grid.Children.Add(stackLayout);
+
+		// CollectionView
+		collectionView = new CollectionView
+		{
+			IsGrouped = true,
+			CanReorderItems = true,
+			CanMixGroups = true,
+			AutomationId = "CollectionView12008"
+		};
+		collectionView.SetBinding(ItemsView.ItemsSourceProperty, "GroupedItems");
+
+		// Group Header Template
+		collectionView.GroupHeaderTemplate = new DataTemplate(() =>
+		{
+			var headerGrid = new Grid
+			{
+				BackgroundColor = Colors.LightBlue,
+				Padding = 10,
+				ColumnDefinitions = new ColumnDefinitionCollection
+				{
+					new ColumnDefinition { Width = GridLength.Star },
+					new ColumnDefinition { Width = GridLength.Auto }
+				}
+			};
+
+			var headerLabel = new Label
+			{
+				FontAttributes = FontAttributes.Bold,
+				FontSize = 16
+			};
+			headerLabel.SetBinding(Label.TextProperty, "GroupName");
+			headerLabel.SetBinding(AutomationIdProperty, new Binding("GroupName", stringFormat: "GroupHeader12008{0}"));
+
+			var countLabel = new Label
+			{
+				FontSize = 12
+			};
+			countLabel.SetBinding(Label.TextProperty, new Binding("Count", stringFormat: "Count: {0}"));
+			countLabel.SetBinding(AutomationIdProperty, new Binding("GroupName", stringFormat: "GroupCount12008{0}"));
+
+			headerGrid.Children.Add(headerLabel);
+			headerGrid.Children.Add(countLabel);
+			Grid.SetColumn(headerLabel, 0);
+			Grid.SetColumn(countLabel, 1);
+			return headerGrid;
+		});
+
+		// Item Template
+		collectionView.ItemTemplate = new DataTemplate(() =>
+		{
+			var itemGrid = new Grid
+			{
+				Padding = 10,
+				BackgroundColor = Colors.LightGray,
+				Margin = new Thickness(2)
+			};
+
+			var itemLabel = new Label
+			{
+				FontSize = 14
+			};
+			itemLabel.SetBinding(Label.TextProperty, "Name");
+			itemLabel.SetBinding(AutomationIdProperty, new Binding("Name", stringFormat: "Item12008{0}"));
+
+			itemGrid.Children.Add(itemLabel);
+			return itemGrid;
+		});
+
+		Grid.SetRow(collectionView, 1);
+		grid.Children.Add(collectionView);
+
+		Content = grid;
+	}
+
+
+	private void OnCreateEmptyGroupClicked(object sender, EventArgs e)
+	{
+		if (this.BindingContext is Issue12008ViewModel viewModel)
+		{
+			viewModel.CreateEmptyGroup();
+			statusLabel.Text = "Status: Empty group created";
+		}
+	}
+}
+
+public class Issue12008ViewModel : INotifyPropertyChanged
+{
+	private ObservableCollection<Issue12008Group> _groupedItems;
+
+	public ObservableCollection<Issue12008Group> GroupedItems
+	{
+		get => _groupedItems;
+		set
+		{
+			_groupedItems = value;
+			OnPropertyChanged();
+		}
+	}
+
+	public Issue12008ViewModel()
+	{
+		InitializeData();
+	}
+
+	private void InitializeData()
+	{
+		GroupedItems = new ObservableCollection<Issue12008Group>
+			{
+				new Issue12008Group("GroupA", new List<Issue12008Item>
+				{
+					new Issue12008Item("ItemA1"),
+					new Issue12008Item("ItemA2"),
+					new Issue12008Item("ItemA3")
+				}),
+				new Issue12008Group("GroupB", new List<Issue12008Item>
+				{
+					new Issue12008Item("ItemB1"),
+					new Issue12008Item("ItemB2")
+				}),
+				new Issue12008Group("GroupC", new List<Issue12008Item>
+				{
+					new Issue12008Item("ItemC1")
+				})
+			};
+	}
+
+	public void CreateEmptyGroup()
+	{
+		var emptyGroup = new Issue12008Group("EmptyGroup", new List<Issue12008Item>());
+		GroupedItems.Add(emptyGroup);
+	}
+
+	public event PropertyChangedEventHandler PropertyChanged;
+
+	protected virtual void OnPropertyChanged([System.Runtime.CompilerServices.CallerMemberName] string propertyName = null)
+	{
+		PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
+	}
+}
+
+public class Issue12008Group : ObservableCollection<Issue12008Item>
+{
+	public string GroupName { get; }
+
+	public Issue12008Group(string groupName, IEnumerable<Issue12008Item> items) : base(items)
+	{
+		GroupName = groupName;
+	}
+}
+
+public class Issue12008Item
+{
+	public string Name { get; }
+
+	public Issue12008Item(string name)
+	{
+		Name = name;
+	}
+}
+

src/Controls/tests/TestCases.Shared.Tests/Tests/Issues/Issue12008.cs

@@ -0,0 +1,44 @@
+#if TEST_FAILS_ON_WINDOWS // The test fails on Windows because Drag and Drop with grouping is not supported on Windows
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.TestCases.Tests.Issues;
+
+public class Issue12008 : _IssuesUITest
+{
+    public Issue12008(TestDevice testDevice) : base(testDevice)
+    {
+    }
+
+    public override string Issue => "CollectionView Drag and Drop Reordering Can't Drop in Empty Group";
+
+    [Test]
+    [Category(UITestCategories.CollectionView)]
+    public void EmptyGroupCreationShouldWork()
+    {
+        App.WaitForElement("CreateEmptyGroupButton12008");
+        App.Tap("CreateEmptyGroupButton12008");
+
+        App.WaitForElement("GroupHeader12008EmptyGroup");
+        App.WaitForElement("StatusLabel12008");
+        var statusText = App.WaitForElement("StatusLabel12008").GetText();
+        Assert.That(statusText, Does.Contain("Empty group created"));
+    }
+
+    [Test]
+    [Category(UITestCategories.CollectionView)]
+    public void DragItemIntoEmptyGroupShouldSucceed()
+    {
+        App.WaitForElement("CreateEmptyGroupButton12008");
+        App.Tap("CreateEmptyGroupButton12008");
+        App.WaitForElement("GroupHeader12008EmptyGroup");
+        App.WaitForElement("Item12008ItemA1");
+        App.DragAndDrop("Item12008ItemA1", "GroupHeader12008EmptyGroup");
+        App.WaitForElement("GroupCount12008EmptyGroup");
+        var groupCountLabel = App.WaitForElement("GroupCount12008EmptyGroup");
+        var countText = groupCountLabel.GetText();
+        Assert.That(countText, Is.EqualTo("Count: 1"), "Item was not moved into the empty group");
+    }
+}
+#endif