Understanding the VCL

The Visual Component Library (VCL) is based on the properties, methods, and events (PME) model. The PME model defines the data members (properties), the functions that operate on the data (methods), and a way to interact with users of the class (events). The VCL is a hierarchy of objects, written in Object Pascal and tied to the C++Builder IDE, that allows you to develop applications quickly. Using C++Builder’s Component palette and Object Inspector, you can place VCL components on forms and specify their properties without writing code.


Properties are characteristics of components. You can see and change properties at design time and get immediate feedback as the components react in the IDE. Well-designed properties make your components easier for others to use and easier for you to maintain.


Methods are functions that are members of a class. Class methods can access all the public, protected and private properties and data members of the class and are commonly referred to as member functions.


Event driven programming (EDP) means just that—programming by responding to events. In essence, event driven means that the program does not restrict what the user can do next. For example, in a Windows program, the programmer has no way of knowing the sequence of actions the user will perform next. They may pick a menu item, click a button, or mark some text. So, EDP means that you write code to handle whatever events occur that you're interested in, rather than write code that always executes in the same restricted order.


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