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Thisform Gotchas! Wow!
Message
From
06/12/2000 23:49:49
Gavin Reid
L & M Marketing Pty Ltd
Frenchs Forest, Australia
 
 
To
06/12/2000 22:32:12
General information
Forum:
Visual FoxPro
Category:
Forms & Form designer
Miscellaneous
Thread ID:
00450216
Message ID:
00450239
Views:
30
Hi David,

The problem with SET FILTER is due to the fact the once the variable that you're setting the filter to goes out of scope then your filter won't work. Want you want to do is set the filter to the value of a variable without using a hard code reference.

E.g.

Instead of
SET FILTER TO country = ThisForm.cmbCountry.Value

try something like:
cCommand = "SET FILTER TO country = [" + ThisForm.cmbCountry.Value + "]"
&cCommand

Try both of these approaches and after each try a WAIT WINDOW FILTER() and see what appears. You'll notice that in the second approach the Filter is being set the value of the field whereas in the first approach the Filter is referencing the object.

Hope this helps,
Gavin...

>Wouldn't be surprised if there has been some general discussion about this issue in the past. I'd appreciate a pointer to a broader discussion of the issue I raise here.
>
>I just discovered that using a 'thisform' reference in a filter condition is very unhealthy and also that the COUNT function doesn't know what to do with property names having implied references (inside a WITH...ENDWITH block).
>
>The following code generated an unknown member error.
>
>WITH thisform
>
>COUNT FOR logicfuncof(.myproperty) TO nmycnt
>
>ENDWITH
>
>
>OK, fine. I explicitly made the reference be thisform.myproperty and the error went away. But then I even got a wierder error.
>
>The now corrected code still produced an unknown member error....but for a property which was not even in the current form! Ohhhhhhhhhhhh!
>
>In myform1 I do:
>
>SET FILTER TO logicfuncXtof(thisform.otherproperty)
>
>
>Then I fire up modal myform2 which executes the COUNT command above, and the COUNT command results in an 'otherproperty' unknown member error.
>
>I guess this is because:
>
>(1) filter expressions are stored as character strings
>(2) functions like COUNT use an implicit conjuction of the FOR clause with the current filter expression. So, my COUNT statement above really executes:
>
>COUNT FOR logicfuncof(.myproperty).AND.logicfuncXof(thisform.otherproperty) TO nmycnt
>
>
>I feel lucky that the form that executes the COUNT does not have a property with the same name as the one calling it, cause I'm pretty sure the 'thisform' in the implied conjunction would have been happy as a clam to use it without complaining.
>
>This bodes badly for saving and restoring filter context, unless I steer clear of 'this' and 'thisform' in filter expressions.
>
>Any insight on this 'feature' of VFP would be greatly appreciated.
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