Using the .NET ReportViewer Control we are trying to create a generic report viewer app that can display any report on our SSRS server.  We want to pass in one hidden parameter determined at run time and make use of the built-in functionality allowing the user to provide values for additional parameters.  A report could have any number of parameters specific to the report.  

(See code snippet)

The test report has Param1 and an additional string parameter defined in it.  When we run the code, we type something into the additional string parameter and click "View Report".  The additional string parameter is then blanked out and no report is generated.  

We have tried a couple of other methods: If we don't pass any parameters to the report and, instead, enter both in the report viewer control, the report works fine; also, if we pass all parameters in the code-behind the report works fine.  

The problem is we dont know how many parameters there will be for a given report.  So, we would prefer to only pass in the one parameter and have the system determine what to do with the other parameters.  Does anybody know a way to get this to work?

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//The following code passes a single parameter to the server report:
protected void Page_Load(object sender, EventArgs e)
{
   List<Microsoft.Reporting.WebForms.ReportParameter> ParamList = new List<Microsoft.Reporting.WebForms.ReportParameter>();
   ParamList.Add(new Microsoft.Reporting.WebForms.ReportParameter("Param1", "TestValue", false));
   ReportViewer1.ServerReport.SetParameters(ParamList);
   ReportViewer1.ServerReport.Refresh();
}