ReportViewer and passing parameters to report

Hi,

i have  a small req   having dropdown aand button.  dropdown contains projectnames .when user select Projectname  click on gnerate reports button it should get  data  related to the project .Im using MSreportviewer .I dont know how to get report  with dropdown .Without dropdown   if i click on generate button   reportviewer shows all data   working  fine .Any  samples on this type of application?

select  distinct(e.EmpID) ,e.EmpName, e.StartDate,e.EndDate,e.Total,ee.Hotel,ee.Airfare,ee.Meals,
ee.Gas,ee.Tolls,ee.Parking,ee.Misc,ee.Mileage,ee.WeeklyComTotalExpenses, p.WeeklyPerTotalExpenses 
from EmpTimeSheet e  left JOIN  (select CExpID,WeeklyComTotalExpenses, sum(CHotel) as Hotel ,sum(CTransport) 
as Airfare,sum(CMeals) as Meals,sum(CFuel) as Gas,sum(CTolls) as Tolls,Sum(CParking) as Parking,Sum(CMisc) as Misc , 
 sum(CMileage) as Mileage from ComExpensesTable group by CExpID,WeeklyComTotalExpenses)  ee on ee.CExpID=e.EmpID left join 
 PerExpensesTable p ON p.PExpID=e.EmpID  left join DetailsTable d on e.EmpId=d.ServiceID   where d.ProjectName= 'AT&T' ;

 protected void Button2_Click(object sender, EventArgs e)
        {
                string Connection = System.Configuration.ConfigurationManager.ConnectionStrings["Conn"].ConnectionString;
                SqlConnection cn = new SqlConnection(Connection);
                cn.Open();
                string str = "select  distinct(e.EmpID) ,e.EmpName, e.StartDate,e.EndDate,e.Total,ee.Hotel,ee.Airfare,ee.Meals,ee.Gas,ee.Tolls,ee.Parking,ee.Misc,ee.Mileage,ee.WeeklyComTotalExpenses, p.WeeklyPerTotalExpenses from EmpTimeSheet e  left JOIN  (select CExpID,WeeklyComTotalExpenses, sum(CHotel) as Hotel ,sum(CTransport) as Airfare,sum(CMeals) as Meals,sum(CFuel) as Gas,sum(CTolls) as Tolls,Sum(CParking) as Parking,Sum(CMisc) as Misc ,  sum(CMileage) as Mileage from ComExpensesTable group by CExpID,WeeklyComTotalExpenses)  ee on ee.CExpID=e.EmpID left join  PerExpensesTable p ON p.PExpID=e.EmpID  left join DetailsTable d on e.EmpId=d.ServiceID   where d.ProjectName= '" + ddlProjectName1.SelectedItem.Text + "'";
                DataSet ds = new DataSet();
                ReportDataSource datasource=new ReportDataSource (str);
                SqlDataAdapter da = new SqlDataAdapter(str,cn);
                  da.Fill(ds, ddlProjectName1.SelectedValue);
                  ReportViewer1.LocalReport.DataSources.Add(datasource);
            }