Right way to run, kill and keep process running

Question

In my application, which using another application (run in tray) to print receipts I need to do those three things:

• Open process when on mainApplication startup
• Close process when mainApplication closing or changing any information about printer
• Keep process alive, if it get any error

First point is quiet easy, I just simply

Process.Start("_ReceiptPrinter.exe");

And process working ;)

But now, the two other issues:

• Closing process. I've tried this code:

  Process[] allProcs = Process.GetProcesses();
  foreach (Process proc in allProcs)
  {
      ProcessThreadCollection myThreads = proc.Threads;
      if (proc.ProcessName == "_ReceiptPrinter")
      {
          proc.Close();
      }
  }
  

Unfortunately, I can still see icon in tray, and process is still running.

• Keep process alive. My main application is in WPF, that one from tray is written on WinForms. Maybe there is any way to handle ANY WinForm application exit event (well, any, but not this one, which just simply close it from another application), and reopen it?

Answer 1

The reason you still see a tray icon is that the icons are cached by an external process (windows explorer.)

The reason process.Close() does not close the application is because the application is not processing window messages (as this call simulates a WM_CLOSE request, per classic Windows API.)

The proper way to close the application is process.Close, not process.Kill(), further, as part of app/window close you need to unregister any tray icons you've registered with the system. This way any normal closure of your application will properly clean-up the tray.

Further, you can use a "critical finalizer" which would be guaranteed to run before application exit, except in total catastrophe scenarios.

Answer 2

proc.Close() asks it to close but there is no guarantee. Use:

proc.Kill();