protected void GridViewNotas_Sorting(object sender, GridViewSortEventArgs e)
        {
            DataTable dataTable = GridViewLibreta.DataSource as DataTable;

            if (dataTable != null)
            {
                DataView dataView = new DataView(dataTable);
                dataView.Sort = e.SortExpression + " " + ConvertSortDirectionToSql(e.SortDirection);

                GridViewLibreta.DataSource = dataView;
                GridViewLibreta.DataBind();
            }
        }
 protected void GridViewNotas_PageIndexChanging(object sender, GridViewPageEventArgs e)
 {
     presentador.IniciarVista();
     GridViewLibreta.PageIndex = e.NewPageIndex;
     GridViewLibreta.DataBind();
 }