XL: How to Create a Demand-Loaded Add-in File

In Microsoft Excel versions 5.x and 7.0, it is possible to create a "demand-loaded" add-in file. This article describes the method used to create a demand-loaded add-in file.

A demand-loaded add-in allows you to see the options the add-in provides without actually loading the add-in: when you use one of the functions included with the add-in, the add-in is loaded into memory: demand-loaded add-ins are available in the Function Wizard dialog box even if the add-in itself has not been loaded into memory.

To make a demand-loaded add-in file, follow these steps:

1. Select any Microsoft Excel version 4.0 Macro sheet or worksheet in the workbook that you want to save as an add-in file.
2. On the Insert menu, click Name, and then click Define.
3. In the Define Name dialog box, enter the following values:
   Names in Workbook edit box : __DemandLoad
   
   Refers to edit box : =TRUE
   Note that the word "DemandLoad" is preceded by *two* underscore characters.
4. Click OK.

When you make the workbook into an add-in, by choosing Make Add-In from the Tools menu, and you then use the Add-Ins dialog box to add the file to Microsoft Excel, the add-in will not actually be loaded until you use or recalculate one of the functions, macros, or subroutines defined in the add-in.

When you use the Add-Ins dialog box to add a demand-loaded add-in to Microsoft Excel, a line similar to the following will be added to your EXCEL5.INI file (if you are using Microsoft Excel for Windows): In Microsoft Excel for Windows 95, an entry will be added to your system's registry; in Microsoft Excel for the Macintosh, a change is made to your "Excel Settings (5)" file.

The /F switch signifies to Microsoft Excel that the add-in in question is a demand-loaded add-in. Microsoft Excel will not yet open the add-in file, but it will read the available functions from the add-in and make them available in the Function Wizard dialog box.

In Microsoft Excel for the Macintosh, the "Excel Settings (5)" file is stored in a binary format and can only be read or edited by the Microsoft Excel program.

"Microsoft Excel Developer's Kit," version 5.0, page 382