public bool CrearReticula(Reticula reticula)
        {
            try
            {
                if (db != null)
                    db.Dispose();

                db.Reticula.Attach(reticula);
                db.Entry(reticula).State = EntityState.Added;
                db.SaveChanges();

                return true;
            }
            catch (Exception ex)
            {
                return false;
            }
        }
        public bool ActualizaMateria(Reticula reticula)
        {
            try
            {
                if (db != null)
                    db.Dispose();

                db.Reticula.Attach(reticula);
                db.Entry(reticula).State = EntityState.Modified;
                db.SaveChanges();

                return true;
            }
            catch (Exception ex)
            {
                return false;
            }
        }