How to execute multiple ".ext" with an associate aplication made in C#

Question

I've made an application to do some work with an extension for example ".ext" I added the necessaries entries to the Windows "regedit" for executing the ".ext" when I open it. Now, if I have selected multiple files.ext and I oppen it; then multiples instances of my application arise.

My application receives a String[] args as parameters, so if I open a file.ext then I receive the file path in args[0], the idea is when I open multiple files then receive the first file path as args[0] and the second file path as args[1], and so on, but right now when I open multiple selected files then multiples instances of my applications arise.

The question is: How can I do for execute multiple files.ext and get the paths in my String[] args for all the selected files.ext and not in different instances of my app. Exactly like the VLC player when we select multiples files.mp3 and we open it.

Answer 1

Finally i found an alternative.
Running only an instance of my app with "Mutex", and importing the shell32.dll i did it.
Somthing like this...

 private static bool isAlreadyInstantiated()
    {
        new Mutex(true, "my_app", out mutex_bool);
        return !mutex_bool;
    }


    private static void getSelectedFiles()
    {
        selected_files = new List<SelectedFile>();

        String filename;
        // Required ref: SHDocVw (Microsoft Internet Controls COM Object)
        ShellWindows shell = new SHDocVw.ShellWindows();

        foreach (SHDocVw.InternetExplorer window in shell)
        {

            filename = Path.GetFileNameWithoutExtension(window.FullName).ToLower();
            if (filename.ToLowerInvariant() == "explorer")
            {
                Shell32.FolderItems items = ((Shell32.IShellFolderViewDual2)window.Document).SelectedItems();

                if (selected_files.Count == 0)
                {
                    foreach (Shell32.FolderItem item in items)
                    {
                        if (active_folder == Path.GetDirectoryName(item.Path))
                            selected_files.Add(new SelectedFile("\"" + item.Path + "\"", item.Name, Math.Round(((double)item.Size / (double)1024), 2)));
                        else
                            break;
                    }
                }
                else
                    return;
            }
        }
    }

Answer 2

This article describes how to force only a single instance of your application. You could extend the custom windows message WM_SHOWME described there to pass the command line parameter to your single instance.