Multiple Calls To ServerReport.SetParameters() With Varying Numbers Of Parameters

I'm new to programming with the ReportViewer object and this issue has me stumped: it appears if you have some optional parameters in your report, and a way to refresh that report with different parameter values, the report "remembers" parameter values from previous calls to SetParameters() on subsequent renderings of the report. If a parameter is included in a call to ServerReport.SetParameters() on the first rendering, but not included in a subsequent call and the report is re-rendered, the previous value of the parameter (rather than the default value) appears to be used.



Here's a snippet of some test code I wrote within an ASP.NET 2.0 test application:



protected void Page_Load(object sender, EventArgs e)

{

if (!Page.IsPostBack)

{

this.rptViewer.ServerReport.ReportServerUrl = new Uri(this.txtReportServerUrl.Text);

this.rptViewer.ServerReport.ReportPath = this.txtReportPath.Text;

}

}

protected void btnViewRpt_Click(object sender, EventArgs e)

{

ReportParameter[] rptParams = GetReportParameters();

this.rptViewer.ServerReport.SetParameters(rptParams);

this.rptViewer.ServerReport.Refresh();

}

private ReportParameter[] GetReportParameters()

{

int paramCount = 0;

ReportParameter[] retVal;

string emptyVal = null;

if (txtName.Text != "") paramCount++;

if (txtAddress.Text != "") paramCount++;

if (txtZip.Text != "") paramCount++;

retVal = new ReportParameter[paramCount];

paramCount = 0;

if (txtName.Text != "")

retVal[paramCount++] = new ReportParameter("Name", txtName.Text);

if (txtAddress.Text != "")

retVal[paramCount++] = new ReportParameter("Address", txtAddress.Text);

if (txtZip.Text != "")

retVal[paramCount++] = new ReportParameter("Zip", txtZip.Text);

return retVal;

}



The test report was written to simply echo back the values of the parameters that are specified. The report definition allows NULL to be specified for the parameters.



The test app was written so if I enter a blank value for Name, Address or Zip, the corresponding parameter does not get created in C# and does not get sent to the report server. If I view the report with all three values (parameters) filled in, I see the parameters echoed back to me in my simple report as expected. If I clear the parameter values the first time the report is rendered, none are sent to the report server and I get no values echoed back in my report, also as expected. I can change the values and click on the View Report button and see the new values for the parameters as expected. However, if I clear any previously-specified parameters and click on View Report, the previously-specified values for the ones that are now cleared are still displayed by the report.



So my question is: once a parameter has been sent to the report, how does one "unsend" it on subsequent refreshes? I know I can create the parameter and set its value to null...but I have a situation here where that can cause errors. It'd be better if I could simply leave out the unspecified parameters and have the report refresh and render as if I were rendering it for the first time.



Any suggestions?