How to get report for perticular record only (selected from dropdownlist)?

See more:

C#

Hiii Friends...
I have written following code on my button click event...instead i m getting all records.I want perticular one record for selected value of dropdown..Help me If u guys know the solution..

protected void Page_Load(object sender, EventArgs e)
   {
       if (!IsPostBack)
       {
           //BindGrid();
           BindVoucher();
           //BindDrpDown();
       }

   }

public void BindVoucher()
   {
       string str = string.Format("select VoucherNo from vw_Expense");
       DataTable dt1 = db.GetDataTable(str);
       DropDownList1.Items.Clear();
       DropDownList1.DataSource = dt1;
       DropDownList1.DataBind();
       DropDownList1.Items.Insert(0, "Select");
   }

protected void Button1_Click(object sender, EventArgs e)
    {
        ReportDocument cryRpt = new ReportDocument();
        cryRpt.Load(Server.MapPath("CryRpt.rpt"));
        cryRpt.SetDatabaseLogon("sa", "indmxabeais", @"VISHWANATH\SQL2008", "EMS");

        string sqlstr = string.Format("select VoucherNo,ExpDate,Reimbursetype,Amount,Advance,StaffName from vw_Expense where VoucherNo='" + DropDownList1.SelectedValue + "'");
        DataTable dt = db.GetDataTable(sqlstr);

        cryRpt.SetDataSource(dt);
        CrystalReportViewer1.ReportSource = cryRpt;
        CrystalReportViewer1.RefreshReport();
        
    }