Pass C# Variables to Powershell Engine

I am writing a WinForms application in C# that will ultimately migrate Exchange 2010 mailboxes to a file location (pstStore) in .pst format. The form consists of a collection of textboxes, combo boxes and radio buttons. The command that will do the work is New-MailboxExportRequest –Mailbox… -FilePath… after a button click.

I am accessing the Exchange Management shell and using a runspace to pass the cmdlet and parameters. In the Parameters (-Mailbox and –FilePath) I want to pass the values of the textboxes and combo boxes. How do I do this in C#?

FYI… I’m using the same code to populate a combo box with all of the mailboxes from the exchange database. So the code works for that purpose so, I thought I could also use it to pass some variables into with the AddParameter method.

Here is the code from the click event:

 InitialSessionState iss = InitialSessionState.CreateDefault();
    PSSnapInException warning;          iss.ImportPSSnapIn("Microsoft.Exchange.Management.PowerShell.E2010",out warning);
    using (Runspace myrunspace = RunspaceFactory.CreateRunspace(iss))
    {
       myrunspace.Open();                                
       using (PowerShell powershell = PowerShell.Create())                    
        {              powershell.AddCommand("Microsoft.Exchange.Management.PowerShell.E2010\\New-MailboxExportRequest")
    powershell.AddParameter("Mailbox", "UserMailbox");
    powershell.AddParameter("FilePath", "ExchAdmin");
    powershell.AddParameter("","");
    powershell.Runspace = myrunspace;
    Collection<PSObject> results = null;
    try
    {
       results = powershell.Invoke(); //Runs the cmdlet synchronously  
    }
    catch (RuntimeException ex)
     {
        foreach (PSObject thisResult in results)
        {
           lstBoxStatus.Items.Add(thisResult); //sending the result to a status window
        }
     }                
     myrunspace.Close();
    }