Enhance aggregate functions (like Sum) in footers so they support expression columns in RadGridView. See the attached project. It works for DataColumn, but raises an exception that no suitable generic Sum method could be found when I set the Sum footer for an expression column.
Thank you for your feedback. As a workaround on this case, I can suggest defining a generic aggregate function based on the Expression you have defined for GridViewExpressionColumn. You can check this online demo for Silverlight: http://demos.telerik.com/silverlight/#GridView/ExpressionColumn or the Calculated Column WPF Demo on how to define an aggregate function for GridViewExpressionColumn. I understand this approach does not apply well when there are many columns, however, this is what we can suggest for the time being.
I am facing the same problem, can you please support this feature.