How to: Create a Simple Custom Function

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This example demonstrates how to create a custom worksheet function. A custom function is an object that implements the ICustomFunction interface. The IFunction.Evaluate method performs all required calculations. To use a custom function, add it to the IWorkbook.CustomFunctions collection.

The following code sample demonstrates how to implement a custom function called SPHEREMASS, which calculates the mass of a sphere made of a material with a specified density. If the density is not provided, the density of water is used.

NOTE

Custom functions are not saved in workbook files.

using DevExpress.Spreadsheet;
using DevExpress.Spreadsheet.Functions;
using DevExpress.XtraSpreadsheet;
// Create a custom function and add it to the global scope.
SphereMassFunction customFunction = new SphereMassFunction();
if (!workbook.Functions.GlobalCustomFunctions.Contains(customFunction.Name))
    workbook.Functions.GlobalCustomFunctions.Add(customFunction);
public class SphereMassFunction : ICustomFunction
{
    const string functionName = "SPHEREMASS";
    readonly ParameterInfo[] functionParameters;

    public SphereMassFunction()
    {   
        // Missing optional parameters do not result in an error message.
        this.functionParameters = new ParameterInfo[] { new ParameterInfo(ParameterType.Value, ParameterAttributes.Required), 
            new ParameterInfo(ParameterType.Value, ParameterAttributes.Optional)};
    }

    public string Name { get { return functionName; } }
    ParameterInfo[] IFunction.Parameters { get { return functionParameters; } }
    ParameterType IFunction.ReturnType { get { return ParameterType.Value; } }
    bool IFunction.Volatile { get { return false; } }

    ParameterValue IFunction.Evaluate(IList<ParameterValue> parameters, EvaluationContext context)
    {
        double radius;
        double density = 1000;
        ParameterValue radiusParameter;
        ParameterValue densityParameter;

        if (parameters.Count == 2)
        {
            densityParameter = parameters[1];
            if (densityParameter.IsError)
                return densityParameter;
            else 
                density = densityParameter.NumericValue;                
        }

        radiusParameter = parameters[0];
        if (radiusParameter.IsError)
            return radiusParameter;
        else
            radius = radiusParameter.NumericValue;

        return (4 * Math.PI) / 3 * Math.Pow(radius,3) * density;

    }
    string IFunction.GetName(CultureInfo culture)
    {
        return functionName;
    }
}
See Also