Microsoft Office 2000/Visual Basic Programmer's Guide

Excel Add-ins

You can build an Excel add-in to add tools or commands to a user's Excel environment. To load an Excel add-in, click Add-ins on the Tools menu and select the add-in from the list, or browse to find it if it doesn't appear in the list.

Once the add-in has been loaded, any toolbars or menu items that it includes appear in Excel. An add-in remains loaded until the user unloads it or until Excel is closed, so tools in the add-in are available to all open workbooks. When the user closes Excel, the add-in is unloaded. It will be reloaded again when Excel is opened only if the add-in is saved to the XLStart folder. For more information, see "Loading an Excel Add-in" later in this chapter.

Several characteristics distinguish an Excel add-in from a typical workbook file:

• An add-in has the file extension .xla to indicate that it is an add-in.
  
  
• When you save a workbook as an Excel add-in, the workbook window is made invisible and cannot be viewed. You can use the invisible workbook and worksheets for storing calculations or data that your add-in requires while it is running.
  
  
• Users can't use the SHIFT key to bypass events that are built into the add-in. This feature ensures that any event procedures you've written in the add-in will run at the proper time.
  
  
• Excel messages (alerts) are not displayed by code running in an add-in. In a standard workbook file, messages appear to verify that the user wants to perform an operation that may result in data loss, such as deleting a worksheet or closing an unsaved workbook file. In an add-in, you can perform such operations without the messages being displayed.

The ODETools\V9\Samples\OPG\Samples\CH11 subfolder on the Office 2000 Developer CD-ROM contains an Excel add-in named ListComboWiz.xla. This add-in provides a wizard for creating a list box or combo box on a worksheet that displays data from a table in a database.

For information about when to create an Excel add-in and when to create an Excel template, see "Excel Templates" later in this chapter.