Chapter 11: Creating Add-Ins and COM Add-Ins

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This chapter introduces the concept of add-ins. In this chapter, you'll learn what an add-in is, how to load and unload add-ins from Microsoft Excel, some common add-ins supplied with Excel, and how to create your own Excel add-in.

Introducing Add-Ins

Add-ins allow you to extend Excel by adding commands and features to those normally found in Excel. These commands and features can be found in many different places, including files that were installed with Excel, the Microsoft Office Web site (http:// office.microsoft.com), and programs that you develop yourself. Once installed, an add-in works like any other menu command or function.

There are three main types of add-ins: Excel add-ins, COM add-ins, and automation add-ins. Excel add-ins are based on macros that are written in Microsoft Visual Basic for Applications (VBA) and stored in a special type of workbook, called a Microsoft Office Excel Add-in, that has a file type of .xla. COM and automation add-ins are created using a compiled language such as Visual Basic or Visual C++.

There are two main reasons add-ins are used. First, an add-in provides a way to easily extend the capabilities of Excel in such a way as to make it appear to the user that the capability was originally included in Excel. This means that programmers and third-party developers can provide easy-to-use tools that can simplify the life of the average user.

Second, add-ins don't use any system resources until they are explicitly loaded into Excel. This improves the overall performance of Excel for users who don't need the extra capabilities, while making it easy for those individuals who want the extra capabilities to access them.

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