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

284 The Fundamentals of Visual FoxPro 6.0
There are times when you might want the behavior of an event to be suppressed. (Are you
picturing the peasant in Monty Python and the Holy Grail, hollering, “He’s repressing me…”?)
For example, you can create your own pick list with a grid that features incremental
search—as the user types a character, the highlight in the pick list repositions itself to the
nearest entry containing those characters. The grid would have a text box in the column that’s
being searched. As you know, the default behavior of the KeyPress event of a text box is to
display the character typed in the text box. You don’t actually want the character typed to be
displayed, so you would want that behavior—displaying the character—to be overridden.
Use the NODEFAULT keyword in the event’s method to do this. For example, you could
write code to trap the character being typed, perhaps storing it to a property of the pick list, and
then using NODEFAULT to prevent the character from being displayed, like so:
* they pressed an alphanumeric key
nodefault
* append the last key pressed to the keyboard buffer property
this.cStuffInKBBuffer = this.cStuffInKBBuffer + chr(nKeyCode)
* look for the complete string
if not seek(upper(this.cStuffInKBBuffer))
go this.nCurRecNum
endif
The actual code would be more complex because you would want to test for the time
elapsed between keypresses, but you get the idea.
Calling a parent’s method in addition to the local method
Another task you’re likely want to perform is to call the parent’s method in addition to the code
in the current method. In other words, this time you’re mixing the blue and the yellow colors,
and want green. You can reference the code of the parent class using the :: operator (referred to
as the scope resolution operator) or the DODEFAULT() keyword. The DODEFAULT()
keyword is usually preferred because you don’t have to know the name of the parent class
you’re referencing.
Suppose the parent class is named cmdDrill and you’ve subclassed it with a name of
cmdDrillLocation. The click event of cmdDrill has the following code:
beep()
If you simply put code in the Click method of the cmdDrillLocation subclass, you would
end up overriding any code in the cmdDrill class’s Click method. To call the BEEP code in the
cmdDrill class as well as the code in the Click event of the cmdDrillLocation class, you would
use the following code:
Dodefault()
or
cmdDrill::click()