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C++ Class Frameworks and the Visual Component Model
The Visual Component Library: The New
Kid on the Block
In 1995 Borland introduced a revolutionary new product called Delphi. It was an instant hit.
Delphi offered rapid application development (RAD) using something called components.
Components are objects that can be dropped on a form and manipulated via properties,
methods, and events. It’s visual programming, if you will.
The concept of form-based programming was first popularized by Microsoft’s Visual Basic.
Unlike Visual Basic, though, Delphi used a derivative of Pascal as its programming language.
This new language, called Object Pascal, introduced OOP to the Pascal language. In a sense,
Object Pascal is to Pascal what C++ is to C. Delphi and Object Pascal represented the
marriage of object-oriented programming and form-based programming. In addition,
Delphi could produce standalone executables. Real programs. Programs that did not require
a runtime DLL in order to run; programs that were compiled, not interpreted; programs that
ran tens of times faster than Visual Basic programs. The programming world was impressed.
Delphi didn’t just throw Object Pascal at you and let you flounder. It also introduced the
Visual Component Library (VCL). VCL is an application framework for Windows programming
in Object Pascal. But VCL is not really comparable to OWL and MFC. Yes, it is a
framework, but the core is very different. It is different primarily because it was designed
around the concept of properties, methods, and events.
You may be wondering why I’m talking about Delphi. The reason is simple—it’s because the
very same VCL that is the heart of Delphi is also the heart of C++Builder. That may come
as a shock to you. If you are coming from a C++ background, you might be scratching your
head right now, wondering how that works. If you are coming from a Pascal background,
you’re probably grinning from ear to ear. If you are coming to C++Builder from any other
type of background, you probably don’t care either way. In the end, it doesn’t really matter
because it works. Let’s look a little deeper into VCL.
Components
As I talked about on Day 1, “Getting Your Feet Wet,” VCL components are objects that
perform a specific programming task. VCL components are wrapped up in Object Pascal
classes. From this point on in this book, we will be encountering components on a daily basis.
I won’t spend a lot of time explaining every detail of components right now because you will
see by example how components work as you go through the rest of the book. Tomorrow I’ll
explain components in more detail.
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