Programming Excel® Services

User-Defined Functions in Excel Services

User-defined functions (UDFs) provide a way for users to add custom-built functionality to a workbook. Conceptually, it might help to think of a UDF as an external library that is callable from a cell in a spreadsheet. Excel Services support only managed UDFs, meaning that these libraries must be built using the .NET Framework. UDFs are a powerful way to extend the surface area of the calculation engine.

The main reason for implementing UDFs is that you require functionality that is not provided by Excel. For instance, the ability to import data from a Web service is a good candidate for a UDF implementation. Or consider a requirement to consume data from a legacy business layer.

UDFs can be called from a ...