VSTO For Dummies

Chapter 2. Building an Add-in

In This Chapter

• Defining an add-in

• Digging into add-in internals

• Building a sample add-in

There is nothing quite like a finished piece of software. Ducks are all in a row and all documented. The t's are dotted, and the i's are crossed — or something like that. Everything is as it should be, except . . . or is it?

Fortunately, thanks to add-ins, you can change the behavior of a lot of software, including Microsoft Office products. The add-in is a piece of additional software that uses the basic functionality of an Office product to make something totally new. You can then use that new piece of functionality in the Office product.

In this chapter, you get a chance to change the way Word works. You're not changing the essential code, perhaps, but you are changing the way the user interacts with the software.

What's an Add-In, Anyway?

In a broad sense, an add-in is a component that you can include into an existing host to provide certain additional functions or features. A host or host application can be virtually any application that supports the add-in model. In the Microsoft Office and VSTO world, an add-in is simply a .NET assembly that gets installed as an extension of the Office suite (Word or Excel, for example).

Most commonly, you'd encounter something similar to an add-in (a plug-in) if you use your Web browser of choice to browse to a Web site that uses content that your browser doesn't recognize. In order to display the content, you create an add-in that ...