Chapter 2. Program Structure

In its simplest form, Visual Basic for Applications is a glue language. This means that as a VB or VBA developer, you concentrate on the interface of and interaction between the objects and controls within the application, gluing the various elements of the application together by writing procedures to perform programmatic tasks and by adding code to handle events. Visual Basic programs are primarily event-driven. Some event or other—such as the user clicking a button— triggers most of the procedures you will write.

From a developer's point of view, one of the most important characteristics of an event-driven application is that, for the most part, the various elements of the program are not interdependent. Sections of your program can be written in complete isolation from the rest. Procedures can be added, removed, or disabled without necessarily having an adverse effect on the whole application. This isn't to say that a Visual Basic application is unstructured; far from it. Before starting to write your VB application, you should have a clear plan of how the various elements of your application are going to interact.

Over the past few years, VB developers have been empowered with a rapidly expanding development environment that can now create custom controls and ActiveX DLLs and EXEs that run either as client-side servers or as remote servers. This movement towards a more object-based ethos has forced a change in the programming style of most VB developers. For the majority of professional VB developers, the days when you could sit in front of a blank form and begin programming without a written plan—altering the architecture of your application on the fly—are long gone.

In this chapter, you will see how to structure a VB program, from starting your program, through the various procedure types at your disposal, and then how you can eventually end your VB program.