Create a custom worksheet function in Excel VBA

Question

I have a faint memory of being able to use VBA functions to calculate values in Excel, like this (as the cell formula):

=MyCustomFunction(A3)

Can this be done?

EDIT:

This is my VBA function signature:

Public Function MyCustomFunction(str As String) As String

The function sits in the ThisWorkbook module. If I try to use it in the worksheet as shown above, I get the #NAME? error.

---

Solution (Thanks, codeape): The function is not accessible when it is defined ThisWorkbook module. It must be in a "proper" module, one that has been added manually to the workbook.

Answer 1

Yes it can. You simply define a VBA function in a module. See http://www.vertex42.com/ExcelArticles/user-defined-functions.html for a nice introduction with examples.

Here's a simple example:

• Create a new workbook
• Switch to VBA view (Alt-F11)
• Insert a module: Insert | Module
• Module contents:

Option Explicit

Function MyCustomFunction(input)
    MyCustomFunction = 42 + input
End Function

• Switch back to worksheet (Alt-F11), and enter some values:

A1: 2
A2: =MyCustomFunction(A1)

Answer 2

Very easily - see Using Microsoft Excel Worksheet Functions in Visual Basic.

Answer 3

The word input needs to be replaced as it is a basic keyword. Try num instead. You can also go further by specifying a type, eg variant.

Function MyCustomFunction(num As Variant)
    MyCustomFunction = 42 + num
End Function