ASP.NET

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        string str = "Select * From Vendor Where(VendorID= '"+ DropDownList1.SelectedValue +"')";
        OleDbCommand cmd = new OleDbCommand(str, conn);
        OleDbDataReader dr=null;
        conn.Open();
        dr = cmd.ExecuteReader();
        while (dr.Read())
        {
            txtvendorname.Text = dr["VendorName"].ToString();
        }
        conn.Close();
    }