Why Should I Use Active Accessibility?
Before starting in on a discussion of how to use Active Accessibility, I need to offer a little more of an explanation as to the purpose of Active Accessibility and how it works.
Active Accessibility uses Component Object Model (COM) technology to expose interfaces that provide a common means of communication among applications. What does that mean? Let's look at an example. Accessible computing often involves more than the guidelines and considerations discussed so far in this chapter. For computers to be accessible to everyone, special devices, known as accessibility aids, sometimes are required. Examples of such aids are screen readers and special input devices. The developers of accessibility aids must create software that communicates with the existing operating system and application software running on the computer. Without Active Accessibility, establishing these communications can be difficult. In order for the accessibility aid software to communicate with the system software, it's required to know or discover a lot of details about the specific types of software. When software applications are created with Active Accessibility, the accessibility aids don't need to know any application-specific details. They can find out what is on the screen and how to use it from the common interfaces exposed by Active Accessibility.
From this you might have figured out that there are two sides to Active Accessibility: the client and the server. The client is the hardware and software for the accessibility aid that is trying to retrieve information. The server is the software application that is exposing accessible interfaces so that the client can easily retrieve the desired user interface information.
My intent when I started writing this was to demonstrate how to make your Visual Basic application available as a server. Unfortunately, after a lot of work and some discussion with Microsoft's Active Accessibility group, I've discovered that the technology isn't quite ready yet for a Visual Basic server. As I said before, Active Accessibility is still very new, and it wasn't designed for use with Visual Basic. So what I've done instead is demonstrate what can be done from the client side. This will at least give you a chance to see how Active Accessibility works and should help prepare you to use it in the future.