The LA Fox Developer Newsletter

March 1998

Subclassing the Visual

FoxPro Base Classes

by Russell Campbell

This article is designed to be ushort and to the point.” It tells

you how to subclass the Visual FoxPro bases classes, but not

why you want to do that. There are plenty of explanations in

books and the trade rags as to why you should subclass the

VFP base classes. Trust me - you don’t want to work directly

with the VFP bases classes. Always work with your

subclassed version of the VFP base classes and you’ll be a

productive, happy programmer with a good bit more hair. That

having been said, let’s get straight to the point of this article.

Open a new, non-wizard form by clicking the File menu and

selecting New (FiIe:New). Choose Form as the file type and

click New File. Ensure that the Form Controls toolbar is visible.

The standard toolbar is shown in figure 1.

If you have a form open and you don’t see this toolbar, click

View:Toolbars, check Form Controls and click OK. Now that

we can

When you pick controls from the standard Forms Control

toolbar, you’re using VFP’s base classes. That is exactly what

you don’t want to do! So how do we get controls on forms

without using this standard toolbar? Well, you’ve got to create

your own toolbar with your own controls. That’s really not hard

and we’ll do it right now.

To get started, click FiIe:New, select Class as the file type, then

click New File. This will bring up the dialog box pictured in

figure 2.

From this dialog box you are about to create a class that is

stored in a class library. We’ll create these classes in a

specific order so that they appear on your toolbar in the same

order as they do on the standard toolbar. Name the class

something meaningful to you. I just use the base class name

with an 'i" at the beginning. The Based On combobox should

say Separator. The Store In field is where you’ll put the name of

the visual class library in which this class will be stored.

Please note that you can click on the button to the right of this

field to navigate to a particular drive and folder and even create

new folders as you go thanks to the Win95 interface. Put the

path and file name in this field and make sure you put it into a

“common” directory for development purposes, not a directory

that contains a particular project. When you’re done, click OK.

When you’ve clicked OK, the Class Designer will appear with

what looks like a teeny, tiny form in it. Leave it be. You have

created a single class (a subclass of the FoxPro separator base

class) in a Visual class library. Not real hard was it? Later,

you’ll add this library as a toolbar into the VFP environment.

Now all you have to do is add a subclass for each of the VFP

base classes to this same visual class library. That’s not hard

— it’s almost the same as adding the first one, but you just

repeat it for each VFP base class.

To do this, simply close the Class Designer. Then click

Tools:Class Browser, navigate to the directory where you

created your visual class library, and double-click on it to open it

in the Class Browser. The Class Browser should look some-

thing like figure 3. Note that it has your separator class in it.

From the Class Browser, you will add additional classes based

on the VFP base classes until you have your visual class library

filled up with subclasses of each of those base classes (actu-

ally in this article we’re only dealing with control classes that

can be placed on a form). Then you’ll be able to add it as a

toolbar to the FoxPro environment and pick controls from itto

be placed on a form. At that point, all your controls will be

based on subclasses of the base classes and not the base

classes themselves. This is the goal we are shooting for. The

next section explains about how to go about these final steps.

Your class library now has one class in it — your subclassed

version of the separator base class. Completing the task of

subclassing all the base classes is just a matter of adding a

(Con’t, page 4)

Figure 1

Figure 3

Figure 2

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