Teach Yourself Borland C++ in 14 Days - portal

Figure 5.1.
The Object Inspector
window.
NEW TERM
NOTE
C++ Class Frameworks and the Visual Component Model
Properties are often tied to access methods that execute when the property is modified.
Things start to get a little confusing at this point. As I said, VCL is
written in Pascal. Pascal uses the term method where C++ uses the term
function. To further muddy the waters, Pascal uses the term function to
refer to a method that returns a value, and the term procedure to refer to
a method that does not return a value. I would be happy enough to call
them all functions (being the old C++ hacker that I am), but when
discussing VCL I will use the Pascal parlance. For the most part I will
use the generic term method.
Properties can be changed at design time (when you are designing your form) and at runtime
(when the program is running through code you write). In either case, if the property has an
access method, that access method will be called and executed when the property is modified.
You have already seen an example of changing a property at design time when you changed
the Left property and watched the form move on the screen. That is one of the strengths of
VCL and how it is used in C++Builder: You can instantly see on the screen what the result
of your design change will be. Not all properties are able to show a visible change on the form
at design time, however, so this does not happen in every case. Still, when possible the results
of the new property value are immediately shown on the form.
To change a property at runtime, you simply make an assignment to the property. When you
make an assignment, VCL works behind the scenes to call the access method for that
property. To change the Left property at runtime, you would use code like this:
MainForm->Left = 200;
141
5