What to Include in a Template

The first step in creating a base template is deciding what to include. The purpose of an application template is to provide the core services that an application is likely to require, but that do not in themselves warrant inclusion in the main application design documentation. The code that makes up the template will in most cases be relevant to many types of application. Some routines will not be needed right from the start, but it is wise to include any routines that might be of use as the project progresses. This section offers a general guide.

Helper Functions

A helper function—such as bFileExists—is an obvious start for your template's library, but so too are the less obvious ones such as ExtractFileName, ExtractPathName, and AppendSlash. At first you might find it hard to think of helper functions to write. You should be able to find a good selection by looking through existing applications. I'm sure you will find many more candidates this way. Looking through existing applications can also help you to identify code that is duplicated between applications and therefore might warrant inclusion. Another way of identifying code for your template is to use a code analyzer on a few of your existing applications. This will help you to identify the routines that are receiving the greatest number of hits, and therefore may prove more useful in template code where you can more easily optimize them.

Common Forms

Common forms can be a real asset to an application. The Common Dialog control is a classic example of a common form. A progress form, About Box, and Message Box are just some of the common forms you can create. Common forms will give your applications a more standard appearance, and again you will not end up with many implementations of the same functionality. A common application MDI form should not be overlooked either. Having such a form will allow you to pre-create the standard menus, such as File, Edit, Window, and Help. Again, this is the type of code that is a bit of a chore to write for each different application.

ActiveX Components

Creating Microsoft ActiveX components can be a powerful way of enforcing business rules. Many applications within an organization will need to access a common set of business rules, creating a uniform look and feel. For example, you could create an ActiveX control that wraps your favorite grid control, and build additional functionality such as allowing the user to cut and paste rows of data. Centralizing these rules into an ActiveX server makes sense. That ActiveX server can then be considered base code.

Subclassing

Subclassing objects and procedures is a powerful technique you can build into your template to change the way that standard Visual Basic elements work. You could, for example, subclass Visual Basic's Load method. "Why would I want to do this?" you ask. Well, imagine an application with a complex-state engine that must control what forms can be loaded depending on application state (not an uncommon requirement). By subclassing the Load method, you will effectively channel every load request via your function. You can then determine what is being loaded and either prevent the load from occurring, or permit it. In effect, all the state code is in a single place. Programmers need not worry if it is safe to load a particular object—they just make the call as normal and the subclassed method takes care of the rest. Couple this into your menu control logic and you have the potential to control your application state from a single point! You can subclass many other Visual Basic elements. I will explain how to do this in more detail later in the chapter.

Now you should have a few ideas to start with. Remember that building an application template is a task that should be treated as a project in its own right. Time and budget will need to be allocated for the task; therefore, it makes sense to pin down the requirements beforehand. The success of your template will very much depend on the thought that has gone into its design. In the following sections, I will explain how to perform some of the tasks we have described so far.