how to retain viewstate for the dynamic controls created in GRIDVIEW

i am creating dynamic textbox onRowCreated event in gridview control, however when i try to findcontrol i get null

here is how i am dong...

protected void gvORg_RowCreated(object sender, GridViewRowEventArgs e)
{
   if ((e.Row.RowState == (DataControlRowState.Edit | DataControlRowState.Alternate)) || (e.Row.RowState == DataControlRowState.Edit))
    {
      if (e.Row.RowType == DataControlRowType.DataRow)
         {
              txBox txtReg = new TextBox();
              txtReg.ID = "_registration" + e.Row.RowIndex + rowId.ToString();
              txtReg.Text = reg.RegistrationToken;
              e.Row.Cells[7].Controls.Add(txtReg);
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    }
}


  protected void gvOrg_RowUpdating(object sender, GridViewUpdateEventArgs e)
        {
            .....
            ....
             TextBox _registration1 = gvOrg.Rows[e.RowIndex].Cells[7].FindControl("_registration" + e.RowIndex + rowId) as TextBox;   
        }

Have you tried to find it by:

GridView gv = (GridView)sender;
GridViewRow gvr = (GridViewRow)gv.Rows[e.RowIndex];
(TextBox)gvr.FindControl("_registration" + e.Row.RowIndex + "_" + reg.RegistrationId.ToString())

i able to fix my problem here