Chapter 10 Using VFP's Object- Oriented Tools - dFPUG-Portal

266 The Fundamentals of Visual FoxPro 6.0
Thus, when you ship an application, you need to include the classes—the .VCX files—
along with your menus, forms, reports, and other files. Or, if you’re building an executable file,
the build process will compile the classes used in your application just as it does ordinary
programs.
Thus, here’s the answer to the question, “How do changes to a class library get reflected in
the application?” When you change a class, you must ship the new .VCX or a new .EXE that
reflects the new .VCX to the location where the application is running, just as when you
updated a procedure library file.
I’d like to discuss the contents of the .VCX and .SCX files in a bit more depth before
moving on, using a real example to illustrate where all the pointers go.
Suppose your form base class consists of a Visual FoxPro base form and two command
buttons, both from a Visual FoxPro command-button base class, as shown in Figure 10.1. The
form base class is named frmBase, and the VCX that holds this form class is named
BASECLASSES.VCX. If you open BASECLASSES.VCX, you’ll see five records. The first is
just a placeholder. The next three records represent the three objects that make up this class: a
VFP form and two VFP command buttons. If you examined the Class field of these three
records, you’d see they reference Visual FoxPro’s built-in objects. The last record is another
placeholder that you shouldn’t worry about. The key point is that this class definition consists
of three records.
Figure 10.1. A sample form base class consisting
of a Visual FoxPro form and two Visual FoxPro
command buttons.
Next, suppose you were to instantiate a form from this class (don’t worry about exactly
how that process works quite yet), and name this form MYSAMPLE.SCX, as shown in
Figure 10.2. If you opened MYSAMPLE.SCX as a table with the USE command, what would
you see? If you had created a regular form, you’d expect to see three records—one for the form
and one for each of the command buttons, right? But we created this form from a class, which
means that this form is essentially just a pointer to a class. That means you’re going to see only
one record in the .SCX file. The Class field in that record is going to point to frmBase, and the
ClassLoc (class location) field in that record is going to point to BASECLASSES.VCX.