In order for the add-in to run, it must be registered and the Add-in Manager must be able to see it. Building and installing the add-in will create the required registry entries for you. For information on how to build and install an add-in, please see the "Installing the New Add-in" section in Chapter 2. This subject is covered again in Chapter 13. In that chapter you will see a procedure for manually registering and creating the Add-in Manager registry entries.

You can download the code from this book from the Downloads section of the Apress Web site (http://www.apress.com). I trust that you will download the code from there, rather than typing it in from the book. There are two reasons for this. First, typing it in is a time-consuming and error-prone process. Second, there is a lot of code involved in one add-in, and there is at least one add-in in each of the chapters from Chapter 2 through Chapter 12.

Chapter 1: What Is an Add-in?

Overview

"Your footsteps are easier to follow than your advice".

An add-in is a tool that you create programmatically by using objects, methods, properties, collections, and events in .NET's extensibility object model. These objects and their respective methods , properties, and events enable you to automate difficult and tedious tasks within the Visual Studio integrated development environment (IDE). These tasks are usually accomplished in response to an event, such as the mouse being clicked, a form being added to a project, or a control being added to a form. The action may or may not be visible to the developer.

I'm not sure why Microsoft calls this functionality "add-in" instead of "add-on" or "extender". However, it is interesting to note that if you take the letters a and i from "add-in", it could be an abbreviation for artificial intelligence (AI). Without being presumptuous, certain add-in features act like AI. For example, consider the form prompter dialog box, which pops up when you add a form to a project. The dialog box asks you for certain required properties, such as form name , text (caption in earlier versions of Visual Basic), and other properties, such as sizing options and whether the form should stay on top (TopMost) of other forms. The add-in has jumped ahead of the developer and reminded him to fill in certain required information, without his having to bring up or search through the property window. It also keeps him from having forms named Form1, Form2, and so forth.

As is the case with ActiveX components , several third-party software vendors write complex add-ins for Visual Studio. I have developed and marketed commercially three major add-ins: VBCommander, VBXRef, and VBCommander/Pro.