Devexpress gridview problem

when i access on database before binding the gridview the gridview never binding again here some code:

    void Page_Load(object sender, EventArgs e)
{ 
    if (!IsPostBack)
    {
        date.Date = DateTime.Now;
        string mode = Request.Params["mode"].ToString().ToLowerInvariant();
        lblPatientName.Text= Session["PatientName"].ToString();
        switch (mode)
        {
            case "new":
                {
                    Page.Title = "Add New Patient Visit";

                    Session["visitID"] = System.Guid.NewGuid();

                    //get basic data (countrycode,cityCode,districtCode,areaCode) from patientdata table
                    SqlParameter pra = new SqlParameter("@Patientid", Session["PatientID"].ToString());
                    SqlDataReader dr = SqlHelper.ExecuteReader(ConfigurationManager.ConnectionStrings["NetCareConnectionString"].ConnectionString,
                           "PatientPrescriptionInsertPrepare", pra);

                    if (dr.Read())
                    {
                        SqlParameter[] prm = new SqlParameter[7];

                        prm[0] = new SqlParameter("@visitID", Session["visitID"].ToString());
                        prm[1] = new SqlParameter("@Patientid", Session["PatientID"].ToString());
                        prm[2] = new SqlParameter("@Specialization", Session["special"].ToString());
                        prm[3] = new SqlParameter("@countrycode", dr["CountryCode"].ToString());
                        prm[4] = new SqlParameter("@cityCode", dr["CityCode"].ToString());
                        prm[5] = new SqlParameter("@districtCode", dr["DistrictCode"].ToString());
                        prm[6] = new SqlParameter("@areaCode", dr["AreaCode"].ToString());
                        SqlHelper.ExecuteNonQuery(CommandType.StoredProcedure, "PreparePrescrption", prm);
                    }

                }
                break;
        }

    }
}  

when i use the event to binding the grid nothing happen when i remove the code upper there every thing run fine:

 protected void btnAdd_Click(object sender, EventArgs e)
{

    SqlParameter [] prm = new SqlParameter[3];
    prm[0] = new SqlParameter("@visitID", Session["visitID"].ToString());
    prm[1] = new SqlParameter("@Patientid", Session["PatientID"].ToString());
    prm[2] = new SqlParameter("@examinationcode", Session["Examinationcode"].ToString());
    Sql开发者_C百科Helper.ExecuteNonQuery(CommandType.StoredProcedure, "PatientExaminations_insert", prm);
    gvParientInvs.DataBind();
}

You should call the ASPxGridView's DataBind method to force the grid to fetch data from the underlying DataSource. Also, if you set the ASPxGridView's DataSource at runtime, you should do this at every request to the server as it is explained in the

Why might paging (sorting, grouping, filtering) not work in the ASPxGridView?

article.