I have a fortran (unmanaged code) dll as the calculation engine, and a C# form as the GUI.
Now, the calculation in fortran is long, so in order not to bore the users, I decided to use Asynch command to create a progress bar. The fortran dll would be responsible for putting messages in the progress bar as the calculation proceeds.
Any idea how this can be done?
Single responsibility: The UI shoul be responsible for display of the progress information, be it a progress bar or other visual effect. The Fortran should not be aware of how the information is displayed, rather it just emits "events" saying thinggs such "just started", "55%", "almost done" and "whoops that didn't work.
How do the events get passed? You probably need some kind of "buffering" tecnhology, perhaps using (named) pipes, or a message queue technology. Fortran can use C libraries so I guess that once you select a communication technology if that's not supported by Fortran directly you can start by writing a bit of C and then get at that from Fortran.
You have to implement anoter function in Fortran dll that reports progress in numbers. For instance: "GetCalculationProgress" that returns two integers (current iteration and total number of iterations). You call that function periodically in another thread in your C# app and read those values. In Fortran you might have to use global variables to track those.
Besides, Here is a link that explains callback method:
http://xtechnotes.blogspot.com/2008/07/callback-to-c-from-unmanaged-fortran.html