private void txt_nom_rec_PreviewTextInput(object sender, TextCompositionEventArgs e)
{
PlatoBLL ub = new PlatoBLL();
string Nombre = (txt_nom_rec.Text);
dtg_rec.Visibility = Visibility.Visible;
System.Data.DataTable dt = ub.platoList(Nombre);
dtg_rec.ItemsSource = dt.DefaultView;
}