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Adventures with "OleControl Shell.Explorer.2" deleting the temporary files issue.

Posted on 2012-12-28
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Last Modified: 2013-01-02
ok, got my OleControl Shell.Explorer.2 activex control to work and it shows pdfs and graphics files.  But of course it needs a pdf file to exist so I create one.  I am storing the documents in my mssql database as a varchar(max)

So, when my user wants to view the document, I create a temporary file and ole.navigate2 to the file.  

But when I close the form, I want to delete the temporary file but of course it is in use.

So I navigate2 to "About:Blank" but I still have to wait .3 of a second before it is released.

inkey(.3)
delete file (tempfilename)

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Tried a DOEVENTS but no difference.  I also have this after I navigate to the blank page:

DO WHILE (this.Olecontrol1.Busy OR this.Olecontrol1.ReadyState <> 4) 
   DOEVENTS
ENDDO

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but again, still need the delay.  So any ideas, not sure if the inkey(.3) is going to be enough for all my client's slow machines and it seems like a patch and not a solution.
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Question by:peterhupp
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Assisted Solution

by:pcelba
pcelba earned 500 total points
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Yes, the control (or OS) releases the file for deletion after certain delay obviously. I am also navigating to a blank page and waiting for ready state and that's not sufficient in some cases...

So I am attempting to delete the temp file in a loop for 2 seconds:
ldDate = DATE()
lnTime = SECONDS()
llSuccess = .F.
DO WHILE !m.llSuccess AND SECONDS() < m.lnTime + 2 AND DATE() = m.ldDate
TRY
  DELETE FILE ...
  llSuccess = .T.
CATCH
ENDTRY
DOEVENTS FORCE
ENDDO

The advantage of this solution is no delay when the deletion attempt succeeds.
But it still does not ensure the file deletion sometimes. In such case the file waits for temp folder general cleanup which deletes all files older than 1 week from the temp folder when the app exits.
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Accepted Solution

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peterhupp earned 0 total points
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Actually I figured this one out and I think it is the best solution.  By using the open I do not attempt the deletion till it either times out or I am able to get RW access.

   lnAttempts= 0
   lnHandle = -1
   DO WHILE lnHandle=-1 and lnAttempts<51 
      lnAttempts = lnAttempts + 1 
      lnHandle = fopen(this.tmpFileName,12)  
      INKEY(.1)
   enddo
   FCLOSE(lnHandle)
   * if timeout handle that otherwise
   DELETE file (this.tmpFileName)

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This is a subset of my code but it shows the logic of the fopen to test the release of the file.
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Expert Comment

by:pcelba
Comment Utility
Yes, your solution must work because the delay could be more than 5 seconds which is enough even for slow systems.
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Author Comment

by:peterhupp
Comment Utility
I did try the try..delete file.... catch but sometimes it would make VFP crash.
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Author Closing Comment

by:peterhupp
Comment Utility
My solution worked the best and 100% of the time.
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