If you use the Import Editor to control the import of methods from your assembly, your settings are saved in an instruction file, [assembly-name].dll.xnr. The settings are read in by the import tool when the application is built.

As an alternative, you can apply attributes directly to your .NET classes and methods.

You can add atributes to your .NET method to control many aspects of the function's behaviour and how the arguments are treated, including:

• Function name in Excel
• Function category
• Argument names
• Default values and array handling for arguments
• Help text

For example, some XLL+ import attributes have been added to the C# code below:

[XllFunction]
public static string TestFunction(string a, double b, int c, bool d)
{
    return String.Format("a={0};b={1};c={2};d={3}",
        a, b, c, d);
}

[XllFunction("AddTwoNumbers")]
public static int MyAdd(
    [XllArgument("First", Flags=XlArgumentFlags.Optional, DefaultValue="100")]
    int a,
    [XllArgument("Second", Flags=XlArgumentFlags.Optional, DefaultValue="-99")]
    int b)
{
    return a + b;
}

List of Attributes

The table below lists the main attributes:

Attribute	Description
XllFunction	Controls the export of a specific method or property as an Excel add-in function.
XllArgument	Controls the export and marshalling of a single argument of an exported Excel add-in function.

For full details see the .NET Runtime Library Reference.

Using Attributes

To use attributes in an existing .NET library, follow these steps:

1. Add a reference to the XLL+ Reflection Runtime library, Psl.XL6.XnReflect.Runtime.dll. This is located in the bin subdirectory of the XLL+ installation folder.

2. Optionally, add a using statement to your C# code:

   using XllPlus;

3. Add a XllFunction attribute to any functions that you wish to export to Excel.

4. Add XllArgument attributes to any arguments that need special handling.

5. Ensure that your project generates an XML documentation file, and make sure that the comments for all exported functions are up to date.

Inspect the NetWrapAttr walkthrough for more details on how to import a .NET assembly using attributes.

Next: Grouping arguments >>