Running exe opening associated extension

Question

My LabVIEW built application is associated with a specific file type in Windows:
http://social.msdn.microsoft.com/Forums/vstudio/en-US/630ed1d9-73f1-4cc0-bc84-04f29cffc13b/what-regi...
and opens double clicked file using command line argument:
http://forums.ni.com/t5/LabVIEW/passing-files-into-labview-vi-by-opening-the-file/m-p/138968/highlig...
This allows me to _launch_ my application, when user double clicks file with specified extension and process this file.
But it happens only if application is not running.
What should I do if I want to open the double clicked file while my program is running? 
Any system event happening that I can register and process?
The only way I see now is to build an intermediate  application that will be associated with extension, check if main application is running and pass arguments to it.
Solved!
Go to Solution.

Answer 1

Alexander_Sobolev
Well, there were many discussions about it, e.g. 1, 2, 3 and in early days I have tried some ways of DDE implementation in my apps. Maybe, you could use private property of LabVIEW which is named "OS Open Document" (needs SuperSecretPrivateSpecialStuff=True string in Labview.ini for it to be visible in Events' configuration window). More info is presented here and here, and it worked for me... Also I've been searching for more elegant way and have found this article. LabVIEW has already built-in DDE server and your application may receive WM_DDE_EXECUTE message with the help of system API calls. So, I made an example of such receiver - it works when you have registered some file extension in Windows (HKEY_CLASSES_ROOT branch in the registry) and is double-clicking your file. It also works when you double-click a shortcut to your application and when you double-click your app's exe, even when it is already running. It isn't working if you registered your file extension with ddeexec key (equals to open(%1)) together with command key (equals to "Path to your app\App.exe" "%1"). But in this case the private property "OS Open Document" works! And you may even use both methods or may choose one of them.
For the simplicity look at these registry keys. If you registered *.ton file extension you should have
[HKEY_CLASSES_ROOT\.ton]
@="ton_auto_file"
 and
[HKEY_CLASSES_ROOT\ton_auto_file\shell\open\command]
@="\"C:\\Test\\Application.exe\" \"%1\""
 keys in the registry. In this case method 1 will work. If you add this key
[HKEY_CLASSES_ROOT\ton_auto_file\shell\open\ddeexec]
@="open(%1)"
 then method 1 won't work but method 2 ("OS Open Document") will work.
My test program is in the attachment (LV 2011). It requires Windows Message Queue Library (second link is for LV 2009 and greater) for DDE message interception. You may integrate message listener loop in parallel thread in your app and stop it with notifier or similar mechanism.
Attachments:
DDE_Test3.vi ‏35 KB