Custom functions error: 'the expression cannot

Question

In Access 2010 I am trying to use custom VBA functions in a calculated column. I get 'the expression cannot be used in a calculated column'.

Here are my steps:

1. Launch Access 2010.
2. Create a new database "DB".
3. Create a table "Table1" with a text column "Column1". Create a test row with "hello" in Column1.
4. On "Create" ribbon, click "Module" at the upper-right corner, which launches VBA editor.
5. In VBA editor "Project" window, there are two projects "ACWZTOOL" and "DB". Choose "DB" and select "Insert" -> "Module".

6. Write the following code:

   Public Function TestFunc() As String
       TestFunc = "test"
   End Function
   

7. "Debug" -> "Compile DB" passed, "Save" and closed VBA editor. Now "Module1" appears in "Modules" tab in the left pane.
8. In Table1, create a calculated column "Column2", with expression "Len([Column1])", the column works properly with the value in test row being 5.
9. Change the expression to "TestFunc()", the error pops up.
10. I tried a few other built-in functions, it seems only the "basic" ones are supported in expression builder. E.g. "InStrRev()" is also not recognized.

Answer 1

According to this guide, user-defined functions are not allowed in calculated column expressions. The relevant quote is in the "Read It" section:

Be aware that calculated fields cannot call user-defined functions, only built-in functions. In addition, you must supply all parameters for methods that you call, even if the parameters are optional.