C# List的使用

一、List排序

　　采用自定义Sort比较器和Linq

class Persion
    {
        public string name;
        public int age;
}
//自定义Sort方法
private static void sortListClass()
        {
            Persion p1 = new Persion() { name = "huyong", age = 27 };
            Persion p2 = new Persion() { name = "tansha", age = 25 };
            List<Persion> listPersion = new List<Persion>();
            listPersion.Add(p1);
            listPersion.Add(p2);
            listPersion.Sort(sortage);
            foreach (var item in listPersion)
            {
                Console.WriteLine(item.name + ":" + item.age);
            }
        }
        static int sortage(Persion x, Persion y)
        {
            if (x.age < y.age) return -1;                //按age从大到小 降序排列
            else if (x.age == y.age) return 0;
            else return 1;
        }
//linq方法
 private static void sortLinq()
        {
            Persion p1 = new Persion() { name = "huyong", age = 27 };
            Persion p2 = new Persion() { name = "tansha", age = 25 };
            Persion p3 = new Persion() { name = "tansha", age = 27 };
            List<Persion> listPersion = new List<Persion>();
            listPersion.Add(p1);
            listPersion.Add(p2);
            listPersion.Add(p3);

 var lList = from t in listPersion where (t.age == 27) orderby t.name ascending select t;
            foreach (var item in lList)
            {
                Console.WriteLine(item.name + ":" + item.age);
            }
        }

二、用Linq将两个list合并为一个list

  //linq合并两个list,根据某一相同字段
private static void mergeList()
        {
            Persion p1 = new Persion() { name = "hy", province = "jx" };
            Persion p2 = new Persion() { name = "tansha", province = "hn" };
            Persion p3 = new Persion() { name = "ht", province = "gd" };
            List<Persion> listPersion = new List<Persion>();
            listPersion.Add(p1);
            listPersion.Add(p2);
            listPersion.Add(p3);

            Persion p11 = new Persion() { name = "hy", age = 23, sex = "男" };
            Persion p21 = new Persion() { name = "tansha", age = 12, sex = "女" };
            Persion p31 = new Persion() { name = "ht", age = 7, sex = "男" };
            List<Persion> listPersion2 = new List<Persion>();
            listPersion2.Add(p11);
            listPersion2.Add(p21);
            listPersion2.Add(p31);

            //linq合并两个list,根据某一相同字段
            var list = from pp1 in listPersion
                       join pp2 in listPersion2 on pp1.name equals pp2.name
                       select new Persion
                       {
                           name = pp1.name,
                           province = pp1.province,
                           age = pp2.age,
                           sex = pp2.sex
                       };
            foreach (var item in list)
            {
                Console.WriteLine(item.name + ":" + item.age + ":" + item.sex + ":" + item.province);
            }
        }

三、对List里面的某个数据进行操作并保存

lists.Where(q =>q.SellChannelId == ((int)SellChannelType.PB).ToString()).ToList().ForEach(q => q.index = 10);

四、List<T>转化为IQueryable<T>

　　不能直接转换，

IQueryable在数据库端中查询，

IEnumerable在内存上查询。

List<T>支持后者。可以用 list.AsQueryable<T>转换。

五、使用LINQ从List<T>集合中删除指定集合元素

实体类(Author)：

public class Author{
    public int id{get;set;}
   public string firstname{get;set;}
   public string lastname {get;set;}
}

比如有如下的LINQ查询语句：

var authors = from x in authorsList
              select x;

其中，需要从查询集合中删除 firstname=’Bob’ 的所有用户，应该如何实现呢？

方案一：

authorsList = authorsList.Where(x => x.FirstName != "Bob").ToList();
//或者
authorsList.RemoveAll(x => x.firstname == "Bob");

方案二：


var authorsList = new List<Author>()
{
    new Author{ Firstname = "Bob", Lastname = "Smith" },
    new Author{ Firstname = "Fred", Lastname = "Jones" },
    new Author{ Firstname = "Brian", Lastname = "Brains" },
    new Author{ Firstname = "Billy", Lastname = "TheKid" }
};

var authors = authorsList.Where(a => a.Firstname == "Bob");
authorsList = authorsList.Except(authors).ToList();
authorsList = authorsList.Except(authorsList.Where(a=>a.Firstname=="Billy")).ToList();