Did you try something like:
using CrystalDecisions.Shared;
...
private void ParamButton_Click(object sender, System.EventArgs e)
{
ParameterFields myParams = new ParameterFields();
ParameterField myParam = new ParameterField();
ParameterDiscreteValue myDiscreteValue = new ParameterDiscreteValue();
myParam.ParameterFieldName = "Country";
myDiscreteValue.Value = "USA";
myParam.CurrentValues.Add(myDiscreteValue);
myDiscreteValue = new ParameterDiscreteValue();
myDiscreteValue.Value = "Netherlands";
myParam.CurrentValues.Add(myDiscreteValue);
myParams.Add(myParam);
myCrystalReportViewer.ParameterFieldInfo = myParams;
myCrystalReportViewer.ReportSource = MyReportObject;
}
Reference:
Passing Multiple Parameters to a Crystal Report Programmatically[
^]