[Gtk-sharp-list] Check Process state in an GUI app

[Chris Howie]

(Oops, sent this to the wrong list.)

On Jan 21, 2008 12:45 PM, Chris Howie <cdhowie at gmail.com> wrote:
> On Jan 21, 2008 11:58 AM, hellboy195 <hellboy195 at gmail.com> wrote:
> > hi,
> > I'm currently trying to write a very very simple front-end for ffmpeg with
> > gtk#.
> > My Code looks like this:
> >
> > First I check if a file already exits with File.Exits(path)
> > MessageDialog -> Overwrite YesNO.
> >
> > Then the I start ffmpeg with Process.Start().
> > Then I want show a MessageDialog if the process finished so I did it like :
> >
> > while(!proc.HasExited) {}
> > MessageDialog -> "Encoding finished";
> >
> > This is working good but this causes some bugs. E.g: If I do Overwrite it
> > "yes". The MessageDialog isn't destroyed until the process finished. If I
> > delete this while {} it's working correct but the Message appears
> > immediately and not after the process hast Finished. Using if is also not
> > that good I suppose :/
> >
> > Any solution? Thx in advance :)
>
> The problem is that you are waiting for the operation to complete on
> the GUI thread.  You have destroyed the dialog, but Gtk cannot
> actually remove the dialog from the screen until you give control back
> to the main GUI loop.
>
> What you want to do is either add an idle handler or spin off another
> thread to take care of it.  An idle handler would probably be easiest
> for your purpose:
>
> // Message dialog code
> Process proc = ...;
> GLib.Idle.Add(delegate {
>     if (proc.HasExited) {
>         // Show dialog.
>         return false; // Remove this delegate from the idle list.
>     }
>
>     return true; // Run this delegate again when idle.
> });
>
> Note that this approach can burn quite a bit of CPU running the idle
> delegate.  You may want to try attaching an event handler to
> Process.Exited instead:
>
> proc.EnableRaisingEvents = true;
> proc.Exited += delegate {
>     Application.Invoke(delegate {
>         // Show dialog.
>     });
> };
>
> Note that you must call Application.Invoke because the Exited event
> handler will not be running on the GUI thread, and you should not
> touch the GUI from other threads.  Application.Invoke puts a delegate
> in a queue to be executed on the GUI thread the next time the main
> loop is entered.

-- 
Chris Howie
http://www.chrishowie.com
http://en.wikipedia.org/wiki/User:Crazycomputers