private void Atualizar_Click(object sender, RoutedEventArgs e)
{
Turma t = grid.SelectedItem as Turma;
if (t != null)
{
t.Codigo = txtTurma.Text;
t.CursoId = (box.SelectedItem as Curso).Id;
n.Atualizar(t);
}
grid.ItemsSource = n.Listar();
}
