But there may be other areas of the computer you want to react to as well, depending on what you are programming the computer to do. Fortunately, when writing applications that run inside AutoCAD, the programmer doesn't have to do all the system-level reactions such as repainting the display or selecting icons for display. In fact, advanced applications can be written without any reactors in them. That is, you're writing functions that are basically callback functions for the dialog box. As things happen in the dialog box under the control of the user, these functions are called on to respond.
Reactors go way beyond dialog boxes, though.
As a result, your functions will appear to react to these events. As in Windows programming, there are specific types of AutoCAD events that your application can react to. These events include adding or removing objects from the drawing, command starts and stops, drawing saves and so forth. Before exploring the implementation specifics that relate to the various programming tools, let's review some of the basics involved. The first rule of programming reactors is to keep them as short and sweet as possible.