How to update a record in a Gridview using c#

protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
{


    string index = e.RowIndex.ToString();

    lblSet.Text = index;

    SqlConnection con = new SqlConnection("Data Source=MEHDI-PC\\SQLEXPRESS;Initial Catalog=PIMS;Integrated Security=True");


    using (SqlCommand cmd = new SqlCommand())
    {
        string sql = "UPDATE dbo.Dwg_Register SET Ref = @Ref, Dwg_Ref = @Dwg_Ref,Title = @Title, Dwg_Received_Date = @Dwg_Received_Date, Rev = @Rev, Trade = @Trade, Type=@Type,Produced_Date=@Produced_Date,Produced_By=@Produced_By,Submittal_Ref=@Submittal_Ref,Issued_To=@Issued_To,Date_Issued = Date_Issued, Purpose = @Purpose, Status=@Status,Action_Date=@Action_Date from dbo.Dwg_Register where DwgRegID=@DwgRegID";

        cmd.Connection = con;
        con.Open();
        cmd.CommandText = sql;

        cmd.Parameters.Add(new SqlParameter("@Ref", txtRef.Text));
        cmd.Parameters.Add(new SqlParameter("@Dwg_Ref", txtDwgRef.Text));
        cmd.Parameters.Add(new SqlParameter("@Title", txtTitle.Text));
        cmd.Parameters.Add(new SqlParameter("@Dwg_Received_Date", txtDwgReceivedDate.Text == "" ? DBNull.Value : (object)txtDwgReceivedDate.Text));
        cmd.Parameters.Add(new SqlParameter("@Rev", txtRev.Text));
        cmd.Parameters.Add(new SqlParameter("@Trade", ddlTrade.Text));
        cmd.Parameters.Add(new SqlParameter("@Type", ddlType.Text));// == "" ? DBNull.Value : (object)txtDateReceived.Text));
        cmd.Parameters.Add(new SqlParameter("@Produced_Date", txtProducedDate.Text == "" ? DBNull.Value : (object)txtProducedDate.Text));
        cmd.Parameters.Add(new SqlParameter("@Produced_By", ddlProducedBy.Text));
        cmd.Parameters.Add(new SqlParameter("@Submittal_Ref", txtSubmittalRef.Text));
        cmd.Parameters.Add(new SqlParameter("@Issued_To", ddlIssuedTo.Text));
        cmd.Parameters.Add(new SqlParameter("@Date_Issued", txtDateIssued.Text == "" ? DBNull.Value : (object)txtDateIssued.Text));
        cmd.Parameters.Add(new SqlParameter("@Purpose", ddlPurpose.Text));
        cmd.Parameters.Add(new SqlParameter("@Status", ddlStatus.Text));
        cmd.Parameters.Add(new SqlParameter("@Action_Date", txtActionDate.Text == "" ? DBNull.Value : (object)txtActionDate.Text));
        cmd.Parameters.Add(new SqlParameter("@DwgRegID", int.Parse(lblSet.Text)));



        cmd.ExecuteNonQuery();

        if (con != null)
        {
            con.Close();
        }





        lblUpdate.Text = "Record updated sucessfully.";


        MultiView1.SetActiveView(ViewGrid);


        GridView1.EditIndex = -1;
        GridView1.DataBind();
    }
}