IEnumerable相关使用

        #region 初始化数据
        public class Book
        {
            public int ID { get; set; }

            public string Title { get; set; }

            public string Author { get; set; }

            public int Price { get; set; }
        }


        private List<Book> getBook
        {
            get
            {
                List<Book> list = new List<Book>()
                {
                      new Book() {Title = "Title1", Author = "Author1", Price = 10, ID = 1},
                                           new Book() {Title = "Title2", Author = "Author2", Price = 20, ID = 4},
                                           new Book() {Title = "Title3", Author = "Author3", Price = 10, ID = 1},
                                           new Book() {Title = "TOMS", Author = "TOMS", Price = 12, ID = 3},
                                            new Book() {Title = "vI", Author = "vI", Price = -1, ID = -7},
                                             new Book() {Title = "EL", Author = "EL", Price = 100, ID = 9},
                                              new Book() {Title = "WING", Author = "WING", Price = 120, ID = 10},
                };
                return list;

            }
        }
        #endregion

 扩展方法：

 public static class ListExprition
    {


        /// <summary>
        /// 在List集中,查找最大的值
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="source"></param>
        /// <param name="c"></param>
        /// <returns></returns>
        public static int?  FindMax<T>(this IEnumerable<T> source, Func<T, int?> c)
        {
            int? temp = null;
            foreach (var item in source)
            {
                if (temp ==null)
                    temp = c(item);
                else if (temp < c(item))
                    temp = c(item);


            }
            return temp;
        }


        /// <summary>
        /// 在List集中,查找最小的值
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="source"></param>
        /// <param name="c"></param>
        /// <returns></returns>
        public static int? FindMin<T>(this IEnumerable<T> source,Func<T,int?> c)
        {
            int? temp = null;
            foreach (var item in source)
            {
                if (temp == null)
                    temp = c(item);
                else if (temp > c(item))
                    temp = c(item);
                   
            }
            return temp;
        }

        /// <summary>
        /// 求和
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="source"></param>
        /// <param name="c"></param>
        /// <returns></returns>
        public static int? MySum<T>(this IEnumerable<T> source, Func<T, int?> c)
        {

            int? temp = 0;
            foreach (var item in source)
            {

                temp += c(item);
            }
            return temp = (temp == null) ? 0 : temp;
        }


        /// <summary>
        /// 根据条件查询集合
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="source"></param>
        /// <param name="c"></param>
        /// <returns></returns>
        public static IEnumerable<T> MyWhere<T>(this IEnumerable<T> source, Func<T, bool> c)
        {
            foreach (var item in source)
            {
                if (c(item))
                {
                    yield return item;
                }
            }
        }



        public static IEnumerable<TResult> MySelect<T, TResult>(this IEnumerable<T> source, Func<T, TResult> c)
        {
            foreach (var item in source)
            {
                var v = c(item);
                yield return v;
            }
        }


      







    }

 调用实例：

private void button1_Click(object sender, EventArgs e)
        {
            var list = getBook;
            var expandBIG=list.FindMax(p=>p.ID); //查找最大的值
            var expandMIN = list.FindMin(c => c.ID);//查找最小值
            var expandSum = list.MySum(x => x.Price);//价格求和
            var selectModel = list.MyWhere(x => x.ID == 1).ToList() ;//根据条件查询结果
            var selectlist = list.MySelect(x => new { x.ID, x.Price }).ToList();



            MessageBox.Show(expandSum.Value.ToString());
        }