Merge pull request #5610 from sdoroff/datagrid-grouping-bug

Fixed DataGidCollectionView grouping bug

src/Avalonia.Controls.DataGrid/Collections/DataGridCollectionView.cs

@@ -3275,7 +3275,7 @@ namespace Avalonia.Collections
                 addIndex);
 
             // next check if we need to add an item into the current group
-            // bool needsGrouping = false;
+            bool needsGrouping = false;
             if (Count == 1 && GroupDescriptions.Count > 0)
             {
                 // if this is the first item being added
@@ -3302,7 +3302,7 @@ namespace Avalonia.Collections
                 // otherwise, we need to validate that it is within the current page.
                 if (PageSize == 0 || (PageIndex + 1) * PageSize > leafIndex)
                 {
-                    //needsGrouping = true;
+                    needsGrouping = true;
 
                     int pageStartIndex = PageIndex * PageSize;
 
@@ -3340,6 +3340,13 @@ namespace Avalonia.Collections
                 }
             }
 
+            // if we need to add the item into the current group
+            // that will be displayed
+            if (needsGrouping)
+            {
+                this._group.AddToSubgroups(addedItem, false /*loading*/);
+            }
+
             int addedIndex = IndexOf(addedItem);
 
             // if the item is within the current page