How to register a custom filter function and use it in GridControl

Starting from version 11.1 it is possible to register a custom function globally .

To create this function, it is necessary to implement the ICustomFunctionOperatorBrowsable interface. If you wish your custom function to be evaluated on the server side (for instance, when Server Mode is used) it is necessary to implement the ICustomFunctionOperatorFormattable interface.
Finally, to register a custom function you should call the CriteriaOperator.RegisterCustomFunction method with your custom function instance at the application startup.

To show a custom function, for instance, within a column DateTime filter dropdown handle the GridView.ShowFilterPopupDate event. In this event handler create a FunctionOperator instance and pass your custom function name to its constructor. Then, add this FunctionOperator to the e.List collection.

Also, it is possible to use a custom function within FilterEditorControl. To use the FilterEditorControl rather than a regular FilterControl in a grid, set the GridView.OptionsFilter.DefaultFilterEditorView property to any value except for Visual. So, you can enter your function in the FilterEditorControl by choosing the Text tab.

This example illustrates how to add a custom function that will determine whether or not a processed date is a day off and show it in a column DateTime filter dropdown.