Frequently Asked Questions About Excel Services UDFs

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.

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.

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;
        }        
    }
}

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

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

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.