Update CustomGrid.cs

GridDemo/Controls/CustomGrid.cs

@@ -1,3 +1,4 @@
+using System.Collections.Specialized;
 using System.Linq;
 using Avalonia;
 using Avalonia.Controls;
@@ -54,6 +55,9 @@ namespace GridDemo
                 RowDefinitions.Clear();
                 RowDefinitions.AddRange(rows);
 
+                // HACK
+                ChildrenChanged(this, new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Reset));
+
                 InvalidateMeasure();
                 InvalidateArrange();
             }