Here are some frequently asked questions about Excel Services user-defined functions (UDFs).
Creating Managed-Code UDFs
What is a supported UDF class?
The UDF class in a UDF assembly must be public. It can be sealed. It cannot be abstract, internal, or private. It must have a parameterless, public constructor. For languages that automatically generate a parameterless, public constructor (for example, C#), you can have no constructor at all.
What is a supported UDF method?
The UDF method in a UDF assembly must be public. The UDF method must be thread-safe.
A UDF method cannot have:
ref or out parameters
retval attributes
Optional arguments
unsupported data types
The UDF method must also have a supported return type. For a list of supported data types, see the "Data Types" section of this topic.
Can I call a Web service from a UDF assembly?
Yes. For an example, see the following UDF sample code. Also see How to: Create a UDF That Calls a Web Service.
using System;
using System.Collections.Generic;
using System.Text;
using Microsoft.Office.Excel.Server.Udf;
using UdfWS.dk.iter.webservices;
namespace UdfWS
{
[UdfClass]
public class MyUdfClass
{
// Instantiate the Web service. The Web service used is at
// http://webservices.iter.dk/calculator.asmx
Calculator calc = new Calculator();
[UdfMethod]
public int MyFunction()
{
int i;
i = (i + 88) * 2;
return i;
}
[UdfMethod(IsVolatile = true)]
public double MyDouble(double d)
{
return d * 9;
}
[UdfMethod]
public int AddMe(int a, int b)
{
int c;
// Call the Web service Add method
c = calc.Add(a, b);
return c;
}
}
}
Imports System
Imports System.Collections.Generic
Imports System.Text
Imports Microsoft.Office.Excel.Server.Udf
Imports UdfWS.dk.iter.webservices
Namespace UdfWS
<UdfClass> _
Public Class MyUdfClass
' Instantiate the Web service. The Web service used is at
' http://webservices.iter.dk/calculator.asmx
Private calc As New Calculator()
<UdfMethod> _
Public Function MyFunction() As Integer
Dim i As Integer
i = (i + 88) * 2
Return i
End Function
<UdfMethod(IsVolatile := True)> _
Public Function MyDouble(ByVal d As Double) As Double
Return d * 9
End Function
<UdfMethod> _
Public Function AddMe(ByVal a As Integer, ByVal b As Integer) As Integer
Dim c As Integer
' Call the Web service Add method
c = calc.Add(a, b)
Return c
End Function
End Class
End Namespace
Data Types
What are the data types that can be used as UDF parameters?
The supported data types are as follows:
Numeric types: Double, Single, Int32, UInt32, Int16, UInt16, Byte, Sbyte
String
Boolean
Object arrays: one- or two- dimensional arrays, that is, object [] and object [,]
DateTime
What are the supported return value types?
The supported return value types are as follows:
Numeric types: Double, Single, Int32, UInt32, Int16, UInt16, Byte, Sbyte
String
Boolean
Object arrays: one- or two-dimensional arrays, that is, object [], object [,], int[] and int[,])
DateTime
Object
XLLs
Are XLLs supported?
Not directly. Excel Services will load and call only managed-code UDFs. However, you can write a managed-code wrapper to call the XLLs and deploy the XLLs to the server, together with the managed-code wrapper assembly.