在引用之前如何确保类是有效的？

    public class Person
    {
        public string FullName { get; set; }
        public int? PhoneNumber { get; set; }
        public int? CarQTY { get; set; }
    }

如果有人没有完全填充对象，我想抛出异常。例如，如果 fullName、phoneNumber 或 carQTY 为 null，我想在 get 方法上引发异常。

我真的必须这样做吗？

    public class Person
    {
        string _FullName;
        int? _PhoneNumber;
        int? _CarQTY;

        private Boolean IsValid()
        {
            Boolean condition = true;
            condition = (FullName != null) && (PhoneNumber != null) && (CarQTY != null);
            return condition;
        }
        public string FullName
        {
            get
            {
                if (!IsValid()) throw new System.ArgumentException("Parameter cannot be null", "fullName is null");
                return _FullName;
            }
            set
            {
                _FullName = value;
            }
        }
        public int? PhoneNumber
        {
            get
            {
                if (!IsValid()) throw new System.ArgumentException("Parameter cannot be null", "phoneNumber is null");
                return _PhoneNumber;
            }
            set
            {
                _PhoneNumber = value;
            }
        }
        public int? CarQTY
        {
            get
            {
                if (!IsValid()) throw new System.ArgumentException("Parameter cannot be null", "carQTY is null");
                return _CarQTY;
            }
            set
            {
                _CarQTY = value;
            }
        }
    }

正如评论中所建议的，强制通过构造函数创建对象是最有效的方法：

    public class Person
    {
        public string FullName { get; private set; }
        public int PhoneNumber { get; private set; }
        public int CarQTY { get; private set; }

        public Person(string fullName, int phone, int carQty){
            FullName = fullName;
            PhoneNumber = phone;
            CarQTY = carQty;
        }
    }

如果您希望允许在创建对象后对其进行修改，那么 setter 也可以是公共的。