Microsoft Office Tutorials and References
In Depth Information
Figure 11-5. The AddIns collection contains information about each add-in known to Excel.
Creating Automation and COM Add-Ins
There are times when it isn’t desirable to create an add-in using Visual Basic for Applications.
Because VBA macros are interpreted, they execute slower than compiled code, which can
seriously affect the performance of computation-intensive add-ins. Also, some functions
aren’t easily implemented using VBA, such as image processing or specialized networking
To address this limitation, all Office applications including Excel have the ability to access an
add-in stored in an external DLL or EXE file. Although there are two different techniques
used to access the external add-ins, both are created with similar programming techniques.
COM add-ins are typically used to respond to clicking a command button or to some other
Excel event such as opening or closing a workbook. Unlike Excel add-ins, you can’t create a
COM add-in that can be used as part of a cell’s formula. Automation add-ins are less
restricted and can be used to respond to Excel events as well as to provide functions that can
be used in a formula.
COM add-ins are defined only through the COM Add-Ins dialog box on the toolbar, whereas
automation add-ins can be defined through the COM Add-Ins dialog box, the Add-Ins dialog
box, or both.