Skip to main content

Pet Peeves: _SCREEN.Activeform

While it's a great product, there are just times that FoxPro really drives me nuts.

A great example? _SCREEN.Activeform.

I know people have ranted about this for years so now it's my turn.

_SCREEN.Activeform returns a pointer to the current form object. But what if there's no current form?

Does it return NULL? An empty string?

No. It errors out.

Does anyone know what the reasoning was here?

Now, you can verify it by doing

IF TYPE("_SCREEN.Activeform")="U"
** Now you KNOW there's no form there.
ELSE
ENDIF

but then you still have to do a

IF NOT ISNULL(_SCREEN.Activeform)

ENDIF

Note that you can't use VARTYPE() because Activeform isn't a variable. (example : VARTYPE(_SCREEN.activeform)) - which is a shame because VARTYPE is the faster of the two.

In that blog post, if you read the comments, you'll hear things like "use PEMSTATUS" instead of Type for objects but the problem here is that ActiveForm IS a valid property for _SCREEN (unless you actually want to refer to it).

I thought I could be clever and maybe look at _SCREEN.FormCount but guess what? If a form is defined but hidden, the ActiveForm is still not there but FormCount is 1.

So the end result is you HAVE to use the slower, uglier type approach to get out of these annoying checks for _SCREEN.Activeform.

IF TYPE("_SCREEN.Activeform")<>"U"
** do something with it - _SCREEN.Activeform
ELSE
** don't do anything otherwise you'll error out.
ENDIF

Now will users notice the performance penalty? That's a tough call - but I do know that it adds three unnecessary lines of code which adds to the Refactorability of a program.

Comments

Anonymous said…
I usually use
IF TYPE("_SCREEN.Activeform.Name") = "C"
*- Do something with it
ENDIF

The typecheck for the property digs into the object if it exists. The type-function internal error catch will catch the error (but sets the MESSAGE() returned value. what's up with that, anyhow?)
No need for the ISNULL() check.

Sietse Wijnker
Anonymous said…
If you have an ActiveX control on a form sometimes _SCREEN.ActiveForm refers to the control, not to the form it's on. I haven't tested if this bug has been fixed in the meantime, because our framework has a method to return the active form that deals with it.

Popular posts from this blog

Blogs and RSS come to Microsoft.com

MS has just introduced their portal and it's pretty comprehensive. Nothing quite like learning that some people use AIM instead of MSN messenger, or that there really may be a need for supporting 4 monitors ( Cyrus Complains ) However, it's really a great sign that MS is serious about supporting the blogging community which seems to have um, exploded in size in the past year. Blogs and RSS come to Microsoft.com

FoxInCloud Stats

FoxInCloud sent this link a while back about their statistics regarding visits to their site: http://foxincloud.com/blog/2017/12/27/VFP-community-lessons-from-foxincloud-site.html What's interesting here is the breakdown of people. Yes, I think it's understandable that the Fox community is getting older. Another factor is the growth of the mobile and web environments taking over development. These environments really do push people towards the newer non-SQL or free SQL/hosted environments but more towards hosted storage options like Amazon and Google. A tool like FoxInCloud that helps MOVE existing applications to the cloud inherently competes with those environments. But FoxInCloud also allows developers to extend their application further by giving them a starting point using Javascript and the basic CSS (such as Bootstrap). If you're not rebuilding your application from scratch, it's certainly a great step forward. FoxPro VFP

5 Great Reasons to attend Virtual FoxFest

What's coming up? Virtual FoxFest is coming up soon (sessions start October 14th). Like last year, the conference is entirely virtual yet includes great breakdown rooms and sessions to add that nice one-on-one feel that you get in person. It's also staggered so you can choose which days you want to attend - October 14th, 20th and 26th. This is great if you can't break away for a consecutive three days. But really, I've gone through the sessions and I see five great sessions that I'm eager to check out. 1. A Decade of Thor (Rick Schummer) Thor has been an extension for Visual FoxPro that many developers swear by, yet many don't know even exists. Visual FoxPro's built-in extensions are great but Jim Nelson's Thor supercharges your IDE. I can't believe it's been ten years - so Rick's session should be able to not just whet your appetite but give you all the reasons you should be using it. 2. VFP C++ compiler.  Last year, we saw DotNetX as well