[AccessD] Building a control class

A.D.

If you are determined to move in this direction and you want to sink events, you would have to 
coerce the generic control object passed in to a specific control type using a case statement that 
determines the control type.  I believe you could also use a variant to pass in the actual control 
(textbox, combo etc) and not have to do a coercion.

I truly do not recommend this approach however.  The number of control types is fixed, so a class 
for each type is usable.  Additionally it turns out that you are really mostly interested in an even 
smaller subset of all of the controls, for example you probably not build a class for the line 
control, the rectangle, the page break, unbound object, picture etc.  To this point I have mostly 
worked with bound controls, as well as the tab, page and command button.  Thus I only have 9 control 
classes.

I guess it really depends on how deep you get into the controls in your forms.

Additionally I use what I call (for lack of a better name) clsGlobalInterface.  It contains code 
that truly is common across the control classes.  As an example it is almost critical to empty 
collections before setting the pointer to the collection to nothing.  So I have a method of 
clsGlobalInterface that will iterate a collection and remove anything in it, calling the term event 
of whatever is in there just in case the object is a class.  This is a mEmptyClass method that could 
reside in each and every control class (or as a function out in a module) but since the code is 
identical, I simply place the code in clsGlobalInterface.

I then dim an instance of clsGlobalInterface in the header of each control class.  I actually expose 
the clsGlobalInterface instance using a property sub in each control class, but mostly it is used by 
the class itself to get at such common code.

It is also possible of course to place code out in a module of the library and call it from the 
control classes, however we are supposed to try really hard to make classes self contained where 
possible.  Thus I prefer to place such code in clsGlobalInterface.

Using this clsGlobalInterface I encapsulate truly global code while keeping my control class 
specific to each control.

John W. Colby
www.ColbyConsulting.com


A.D.Tejpal wrote:
> John,
> 
>     What I have in mind is a generic class, that morphs into a dedicated type as per the control passed to it. For example, if a text box is passed as argument, it acts as pure text box class. Similarly, for a combo box, it functions as pure combo box class.
> 
>     No doubt, the code content for such a class is more than that in tailor made class for single control. However, it offers the advantage of a common place to manage the code. Duplication of certain content across multitude of classes can be avoided. If any common improvement  / enhancement in class code is found necessary, it can be done conveniently at one place. No need to edit all the scattered classes for individual controls.
> 
> Best wishes,
> A.D. Tejpal
> ------------