public class Person
    {
        public string Name{get;set;}
        public string Sex { get; set; }
        public int Age { get; set; }
        public string Address { get; set; }
        public string Province { get; set; }
    }



    public class Father
    {
        public string Name { get; set; }
        public string Sex { get; set; }
        public int Age { get; set; }
        public Son Son { get; set; }
    }


    public class Son
    {
        public string SonName { get; set; }
        public int SonAge { get; set; }
    }

        static XDocument ChangeToXDocument<T>(T entity) where T : class,new() //加约束
        {
            entity = entity ?? new T();
            XDocument doc = new XDocument();
            doc.Add(new XElement("xml"));
            var root = doc.Root;
            List<string> list = new List<string> { "Name", "Age", "Sex" };
            if (entity is Person)
            {
                list.AddRange(new string[] { "Province", "Address" });  //xml文档格式元素节点按照这个顺序填写
            }
            else if (entity is Father)
            {
                list.AddRange(new string[] { "Son", "SonName", "SonAge" });  //xml文档格式元素节点按照这个顺序填写
            }
          
            var proNewList = entity.GetType().GetProperties().OrderBy(p => list.IndexOf(p.Name)).ToList(); //entity实体属性按照list的顺序重新排好了

            foreach (var prop in proNewList)
            {
                var propName = prop.Name;
                if (propName == "Son")//说明要有Son节点,因为Son在这里是一个类，所以得再次调用 ChangeToXDocument<T>(T entity)方法
                {
                    var sonElement = new XElement("Son");
                    var son = prop.GetValue(entity, null) ;//获取Son类中的对象了
                    var subNodes = ChangeToXDocument(son);
                    sonElement.Add(subNodes.Root.Elements());//Son节点添加里面的子节点 
                    root.Add(sonElement);//根节点添加Son节点
                }
                else    //其他类型要做处理，可以在这里做判断处理完再加到root上面
                {
                    root.Add(new XElement(propName, prop.GetValue(entity, null)));
                }

            }
            return doc;
        }

        static void Main(string[] args)
        {

            Person p = new Person();
            p.Name = "校长";
            p.Sex = "男";
            p.Age = 20;
            p.Address = "长隆长隆";
            p.Province = "广东省";
            Console.WriteLine("---------------person-----------------");
            string str = ChangeToXDocument(p).ToString();
            Console.WriteLine(str);


            Console.WriteLine("---------------father-----------------");
            Father f = new Father();
            f.Name = "父亲";
            f.Age = 50;
            f.Sex = "男";
            Son s = new Son();
            s.SonName = "儿子";
            s.SonAge = 20;
            f.Son = s;
            string str1 = ChangeToXDocument(f).ToString();
            Console.WriteLine(str1);

            Console.ReadKey();
        }