Teach Yourself Borland C++ in 14 Days - portal

C++ Class Frameworks and the Visual Component Model
When you drop a component on a form, C++Builder creates code that inherits a class from
the VCL class that represents that component. A pointer to the object is created so that you
can access the objects in your code. C++Builder uses the Name property in the class name and
for the pointer variable’s name. When we created the sample application earlier, we placed
a memo component on the form. At that point C++Builder derived a class from TMemo and
created an instance of that class. Similarly, when we created a button on the form, C++Builder
derived a class from TButton and created an instance of that class. Before any of that took
place, C++Builder had already derived a class from TForm and, of course, created an instance
of that class to represent the form.
Some understanding of the VCL classes is obviously required to begin working with VCL.
Although I cannot review each and every class in VCL, I can hit the high points. Let’s take
a look at some of the classes that you will use most frequently.
Form and Application Classes
Form and application classes represent forms and the Application object in VCL. These
classes are all derived from TComponent and indeed are components themselves. They are listed
separately to distinguish them from the controls you drop on a form.
TApplication
The TApplication class encapsulates the basic operations of a Windows program. TApplication
takes care of things like managing the application’s icon, providing context-sensitive help,
and doing basic message handling. Every C++Builder application has a pointer to the
TApplication object called Application. You will use the TApplication class primarily to
execute message boxes, manage context-sensitive help, and set hint text for buttons and status
bars. TApplication is a bit of an oddity in VCL in that some of its properties (Icon, HelpFile,
and Title) can be set via the Application page of the Project Options dialog box.
TForm
The TForm class encapsulates forms in VCL. Forms are used for main windows, dialog boxes,
secondary windows, and just about any other window type you can imagine. TForm is a
workhorse class in VCL. It has nearly 60 properties, 45 methods, and about 20 events it can
respond to. I am going to discuss forms in detail tomorrow, so I won’t go into a lot of detail
right here.
Component Classes
This group encompasses a wide range of classes. This group could be further broken down
into separate categories, which I’ve done in the following sections.
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