Fix: Fixed crash that could occur when dragging in grouped grid layout (#14654)

Author: hishitetsu

src/Files.App/Views/Layouts/BaseLayoutPage.cs

@@ -958,7 +958,7 @@ protected virtual void Page_CharacterReceived(UIElement sender, CharacterReceive
 			}
 		}
 
-		protected void FileList_DragItemsStarting(object sender, DragItemsStartingEventArgs e)
+		protected virtual void FileList_DragItemsStarting(object sender, DragItemsStartingEventArgs e)
 		{
 			try
 			{
@@ -1094,7 +1094,7 @@ private async void Item_DragOver(object sender, DragEventArgs e)
 			}
 		}
 
-		private async void Item_Drop(object sender, DragEventArgs e)
+		protected virtual async void Item_Drop(object sender, DragEventArgs e)
 		{
 			var deferral = e.GetDeferral();
 
@@ -1282,7 +1282,7 @@ protected void ItemsLayout_DragOver(object sender, DragEventArgs e)
 			CommandsViewModel?.DragOverCommand?.Execute(e);
 		}
 
-		protected void ItemsLayout_Drop(object sender, DragEventArgs e)
+		protected virtual void ItemsLayout_Drop(object sender, DragEventArgs e)
 		{
 			CommandsViewModel?.DropCommand?.Execute(e);
 		}

src/Files.App/Views/Layouts/GridLayoutPage.xaml

@@ -819,7 +819,9 @@
 					CanDragItems="{x:Bind AllowItemDrag, Mode=OneWay}"
 					ContainerContentChanging="FileList_ContainerContentChanging"
 					DoubleTapped="FileList_DoubleTapped"
+					DragEnter="ItemsLayout_DragEnter"
 					DragItemsStarting="FileList_DragItemsStarting"
+					DragLeave="ItemsLayout_DragLeave"
 					DragOver="ItemsLayout_DragOver"
 					Drop="ItemsLayout_Drop"
 					FocusVisualPrimaryThickness="0"

src/Files.App/Views/Layouts/GridLayoutPage.xaml.cs

@@ -639,6 +639,47 @@ private void SelectionCheckbox_PointerCanceled(object sender, PointerRoutedEvent
 			UpdateCheckboxVisibility((sender as FrameworkElement)!.FindAscendant<GridViewItem>()!, false);
 		}
 
+		// To avoid crashes, disable scrolling when drag-and-drop if grouped. (#14484)
+		protected override void FileList_DragItemsStarting(object sender, DragItemsStartingEventArgs e)
+		{
+			if (ParentShellPageInstance?.FilesystemViewModel.FilesAndFolders.IsGrouped ?? false)
+				ScrollViewer.SetVerticalScrollMode(FileList, ScrollMode.Disabled);
+
+			base.FileList_DragItemsStarting(sender, e);
+
+			if (ParentShellPageInstance?.FilesystemViewModel.FilesAndFolders.IsGrouped ?? false &&
+				e.Cancel)
+				ScrollViewer.SetVerticalScrollMode(FileList, ScrollMode.Auto);
+		}
+
+		private void ItemsLayout_DragEnter(object sender, DragEventArgs e)
+		{
+			if (ParentShellPageInstance?.FilesystemViewModel.FilesAndFolders.IsGrouped ?? false)
+				ScrollViewer.SetVerticalScrollMode(FileList, ScrollMode.Disabled);
+		}
+
+		private void ItemsLayout_DragLeave(object sender, DragEventArgs e)
+		{
+			if (ParentShellPageInstance?.FilesystemViewModel.FilesAndFolders.IsGrouped ?? false)
+				ScrollViewer.SetVerticalScrollMode(FileList, ScrollMode.Auto);
+		}
+
+		protected override void ItemsLayout_Drop(object sender, DragEventArgs e)
+		{
+			if (ParentShellPageInstance?.FilesystemViewModel.FilesAndFolders.IsGrouped ?? false)
+				ScrollViewer.SetVerticalScrollMode(FileList, ScrollMode.Auto);
+
+			base.ItemsLayout_Drop(sender, e);
+		}
+
+		protected override void Item_Drop(object sender, DragEventArgs e)
+		{
+			if (ParentShellPageInstance?.FilesystemViewModel.FilesAndFolders.IsGrouped ?? false)
+				ScrollViewer.SetVerticalScrollMode(FileList, ScrollMode.Auto);
+
+			base.Item_Drop(sender, e);
+		}
+
 		private void UpdateCheckboxVisibility(object sender, bool isPointerOver)
 		{
 			if (sender is GridViewItem control && control.FindDescendant<UserControl>() is UserControl userControl)