how to programatically show processing screen ( By SPLongOperation )

It would be nice if we may possibly show a processing like the not more than that comes out of the box in Sharepoint 2010 which says “Processing… Delight wait while your changes are processed.”

This can be achieved programatically by the following code

SPLongOperation.BeginOperation beginOperation = null;

if (beginOperation == null)
{
    beginOperation = delegate(SPLongOperation longOperation)
    {
        // Long running code here .. 

        longOperation.End("settings.aspx", SPRedirectFlags.RelativeToLayoutsPage, HttpContext.Current, null);
    };
}
SPLongOperation.Start(beginOperation);

longOperation.End() can be used to specify the redirect page when the operation ends. In the above example, it will redirect to the settings page of the site.

Also refer to :
http://peterheibrink.wordpress.com/2009/09/07/splongoperation/

Check it out:SharePoint 2010