how to get sub report Parameters by c#

hi to all
i have a subreport in my main report and it has one storeProcedure as datasource  that has one  sp Parameter like "MyParameter".


i want to get this parameters by c# code ,how can i do this?


in main report we can get paramters using below code but it falling to problem when 
we want to use this code for subreport !!!!!!!




ReportDocument reportDocument;
 reportDocument.Load(pageObject.Server.MapPath(mainreportFilename));


foreach (CrystalDecisions.Shared.ParameterField field in reportDocument.ParameterFields)
//some code 




thanks for any help.