WebApplication4.Models.PosNumberAttribute3.IsValid C# (CSharp) Méthode

        public override bool IsValid(object value)
        {
            if (value == null)
            {
                return true;
            }
            double getal;
            if (double.TryParse(value.ToString(), out getal))
            {

                if (getal >= 0)
                    return true;
            }
            return false;
        }