Excel Get ActiveX References​.vi and closing references -- grrr

Question

I'm new to ActiveX stuff, but eager to learn! 
The "grrr" in my Subject line is a reference to how I feel about LabVIEW's documentation from time to time.  I'm a dinosaur who came from text-based programming, and did a fair amount of C coding, so sometimes with LabVIEW I'm left with this awful feeling in the pit of my stomach like, "Good grief!  How much memory must LabVIEW be hogging up in the background when I use this vi?" or "What happens to those variables (wires) in that subVI when it completes but doesn't close?  What are their statuses when I come back in the next time?" or "What if I put a lot of elements into that array the first time and then started from element zero the second time and just put in a few?  What has happened with the memroy that was allocated when there were a lot of elements?"
Today I'm stewing about this "Excel Get ActiveX References.vi," and what happens to the "ActiveX references" it generates each time I call the subVI in which "Excel Get ActiveX References.vi" lives.  I think that at least one of the "ActiveX references" it generates when I call it is of the type Excel._Application.  Then there appears to be an Excel._Workbook, and others.  You see, I've used "Excel Easy Report.vi" to put some data into an Excel spreadsheet, and I want to tell Excel to do a "Save" on the open spreadsheet.  I think ActiveX is the (a) right way to do that, so I'm wading into the ActiveX fray...  But this "Excel Get ActiveX References.vi" says in its help file, "Do not close ActiveX references opened with the Excel Get ActiveX References VI. References must remain open until the report is closed. Otherwise the error 3001 will occur."  Well, these Excel workbooks that get created by my VI could well stay open until after my LabVIEW VI terminates!
So (finally), here are some of my quesitons:
1)  When I go through my subVI once, pointing to one workbook, I'll get one set of references "created" or "opened" or whatever you call it when ActiveX references spring into existance.  Now, when I exit the subVI, is it going to automatically try to "close" those ActiveX references?  I don't suppose so, since subVI's stay in memory until the calling VI closes.
2)  Now, I come back into my subVI a second time.  New workbook gets created, so I get new references.  Ok, fine.  Uh oh!  What happened to those old references?  I suppose that if I didn't somehow save them off, I've probably lost the ability to get them back (maybe I'm wrong, but I don't need them back), but is LabVIEW going to "close" those old references (from previous times through the subVI) because I can't get to them anymore?  Won't that cause the dreaded error 3001?  If LabVIEW is not going to "close" them, what in tarnation happens to them (the old C programmer in me creeping back out)??  Now it's some oddball, orphaned reference, floating out there, hogging memory, waiting to make something crash intermittently and be a debugging nightmare?
3)  Now, here's the real scary one.  I think I might dodge the "error 3001" bullet in questions 1) and 2), but now let's say the user closes my LabVIEW application while Excel is still open.  All those workbooks are still open.  Presumably, all those ActiveX references I was not supposed to close are still open.  I really hope that LabVIEW is decent enough to close/erase/delete/blow-away (whatever the right word is) all those ActiveX references which were opened/created by "Excel Get ActiveX References.vi" when my program terminates.  But, oh no!  Won't the error 3001 come along then?  I suppose I can just dump it in the shutdown error handling.
Well, thanks for reading my novel.  I don't know what can be done with LabVIEW documentation to make it more satisfying to folks like me, but perhaps someone can weigh in on all my ActiveX questions here.
Thank you in advance,
Steve Brady
Solved!
Go to Solution.

Answer 1

You need to close EVERY ActiveX reference you open.  If you don't you'll end up with some Excel processes running even after LabVIEW exits.  You can see them in Task Manager.
I, personally, don't like the LabVIEW Report Generation Tool Kit for working with Excel.  I don't think it's flexible enough.  I have a growing library of VIs that I've written that open, manipulate, and close Excel.  Some references I pass from VI to VI and some I close right after I use them.  It all depends on what I'm doing.  If I want to enter read or write data from/to a certain range I'll get the range reference, read or write the data, then close it right away because I have no use for it any more.  On the other hand, when I open Excel or a Workbook I keep the reference until I'm done, which could be later in the program.
1)  When I go through my subVI once, pointing to one workbook, I'll get one set of references "created" or "opened" or whatever you call it when ActiveX references spring into existence.  Now, when I exit the subVI, is it going to automatically try to "close" those ActiveX references?  I don't suppose so, since subVI's stay in memory until the calling VI closes.
2)  Now, I come back into my subVI a second time.  New workbook gets created, so I get new references.  Ok, fine.  Uh oh!  What happened to those old references?  I suppose that if I didn't somehow save them off, I've probably lost the ability to get them back (maybe I'm wrong, but I don't need them back), but is LabVIEW going to "close" those old references (from previous times through the subVI) because I can't get to them anymore?  Won't that cause the dreaded error 3001?  If LabVIEW is not going to "close" them, what in tarnation happens to them (the old C programmer in me creeping back out)??  Now it's some oddball, orphaned reference, floating out there, hogging memory, waiting to make something crash intermittently and be a debugging nightmare?
3)  Now, here's the real scary one.  I think I might dodge the "error 3001" bullet in questions 1) and 2), but now let's say the user closes my LabVIEW application while Excel is still open.  All those workbooks are still open.  Presumably, all those ActiveX references I was not supposed to close are still open.  I really hope that LabVIEW is decent enough to close/erase/delete/blow-away (whatever the right word is) all those ActiveX references which were opened/created by "Excel Get ActiveX References.vi" when my program terminates.  But, oh no!  Won't the error 3001 come along then?  I suppose I can just dump it in the shutdown error handling.
1)  No, LabVIEW will NOT close those references.  You need to make sure that happens.
2)  You can save the references in a functional global or use a class but if you're not going to save them close them as soon as you're done with them.
3)  Your user should not be able to close your LabVIEW application without it going through the shutdown routine you've created for your program.  The ABORT button should never be exposed to the user and you should capture and discard the panel close event so your program ALWAYS shuts down is an orderly fashion.  If you don't you will have fragments of Excel hanging around in your operating system and will have to kill those processes using Task Manager.  That should only be a problem during development, not once deployed.
I used to program in C and Assembly many moons ago.  You should have seen my first LabVIEW code.  I go back and look at it just so I can see how far I've come in the last 12 years.  I feel your pain.
Kelly Bersch
Certified LabVIEW Developer
Kudos are always welcome