Thanks for the feedback.

The mentioned error is expected, because our custom formula "GroupByColumnSumFunction" does not exist in the CalcManager. So we need to add this custom function to the CalcManager. For example:

private void Form1_Load(object sender, EventArgs e)

{

   MyCustomFunction custFunc = new MyCustomFunction(ultraGrid1.Rows);

  ultraCalcManager1.RegisterUserDefinedFunction(custFunc);

    ShowFormulaBuilderDialog_2(ultraGrid1.DisplayLayout.Bands[0].Columns["formula5"] as IFormulaProvider);

}

private void ShowFormulaBuilderDialog_2(IFormulaProvider formulaProvider)

{

   FormulaBuilderDialog formulaBuilderDialog = new FormulaBuilderDialog(formulaProvider);

   //formulaBuilderDialog.ShowDialog(this);

   formulaProvider.Formula ="GroupByColumnSumFunction( [part12], [part4] )";

}

Please take a look at the modifications that I made in our sample and let me know if you have any questions.

Regards

If you need any additional assistance don’t hesitate to ask.     

this is the sample

this is video file