C# lambda和Linq

小灰灰 2022-06-06 04:06 226阅读 0赞

1.Action委托 接收参数 无返回值

#region 8.0.1 Action委托 接收参数 无返回值
            public static void C0801Action()
            {
                List<int> list = new List<int> { 1, 2, 3, 4, 5 };
                //遍历打印
                list.ForEach(fe);
                //利用匿名函数
                list.ForEach(delegate (int i) { Console.WriteLine(i.ToString()); });
                //利用lambda表达式打印
                list.ForEach(i => Console.WriteLine(i));
            }
    
            private static void fe(int obj)
            {
                Console.WriteLine(obj.ToString());
            }
            #endregion

2.Predicate 泛型委托：接收一个参数，返回bool类型

static void C0802Predicate()
            {
                var list = GetPigeList();
                list.FindAll(c => c.Age > 100);
                //有多个返回第一个
                var pig = list.Find(c => c.Name == "小猪");
            }

3.func:接收参数，返回参数，但不固定

static void C0802Func()
            {
                var list = GetPigeList();
                //list中年龄大于一的猪
                list.Where(c => c.Age > 1).ToList().ForEach(i => Console.WriteLine(i.ToString1()));
            }

4.Comparison返回一个整数，接收两个同类型的参数

#region Comparison<T>返回一个整数，接收两个同类型的参数
            static void C0804Comparison()
            {
                var list = GetPigeList();
                //原始的
                list.Sort(Query1);
                //匿名委托
                list.Sort(delegate (Pig p, Pig n) { return n.Age - p.Age; });
                //按年龄倒叙排列
                list.Sort((p, n) => n.Age - p.Age);
                list.ForEach(i => Console.WriteLine(i.ToString1()));
            }
            static int Query1(Pig p, Pig n)
            {
                return n.Age - p.Age;
            }
            #endregion

5.SQO方法-标准查询运算符

#region SQO方法-标准查询运算符
            static void C0901Where()
            {
                var list = GetPigeList();
    
                //age>5||Name=""
                list.Where(c => c.Age > 5 || c.Name == "小猪").ToList().ForEach(c => Console.WriteLine(c.ToString1()));
    
                //FirstOrDefault演示
                list.FirstOrDefault(c => c.Age > 5 || c.Name == "小猪");
                list.LastOrDefault(c => c.Age > 5 || c.Name == "小猪");
            }
            //对集合进行排序
            static void C0902Sort()
            {
                var list = GetPigeList();
                //正序
                list.OrderBy(c => c.Age).ToList().ForEach(i => Console.WriteLine(i.ToString1()));
                //正序
                list.OrderByDescending(c => c.Age).ToList().ForEach(i => Console.WriteLine(i.ToString1()));
                //根据最后一个排序
                list.OrderByDescending(c => c.Age).OrderByDescending(c => c.ID).ToList().ForEach(c => Console.WriteLine(c.ToString1()));
                //后面的组合排序用ThenBy
                list.OrderByDescending(c => c.Age).ThenByDescending(c => c.ID).ToList().ForEach(c => Console.WriteLine(c.ToString1()));
            }
            //投影方法
            static void C0904Select()
            {
                var list = GetPigeList();
                //将lis中的Name属性的值获取成一个新的集合
                List<string> nlist = list.Select(c => c.Name).ToList();
    
                //将lis中的Name和Age属性的值获取成一个新的集合,匿名类
                list.Select(c => new { c.Name, c.Age }).ToList().ForEach(c => Console.WriteLine(c.Name + ":" + c.Age));
    
                nlist.ForEach(c => Console.WriteLine(c.ToString()));
            }
            #endregion

6.分页方法Skip（skipNum）.take(页容量)

static void C0905Page()
            {
                int rowCount = 0;
                C0905ByPage(1, 2, out rowCount);
            }
            static List<Pig> C0905ByPage(int pageIndex, int pageSize, out int rowCount)
            {
                rowCount = 0;
                var list = GetPigeList();
                rowCount = list.Count(c => c.Age > 5);
                return list.Where(c => c.Age > 5).Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList();
            }

7.链表查询join

static void C0906Join()
            {
                var piglist = GetPigeList();
                var pigTypeList = GetPigeTypeList();
                //查找piglist集合中的Name和ID值同时和Typelist的TName的值作为一个新的匿名类集合返回
                piglist.Join(pigTypeList, p => p.TypeID, t => t.TypeID, (p, t) => new
                {
                    p.ID,
                    p.Name,
                    t.TName
                }).ToList().ForEach(c => Console.WriteLine(c.ID + ":" + c.Name + ":" + c.TName));
            }

8.分组GroupBy

static void C0907GroupBy()
            {
                var list = GetPigeList();
                //根据TypeID分组
                list.GroupBy(c => c.TypeID).ToList().ForEach(c =>
                {
                    //c代表分组以后的每个小组
                    Console.WriteLine("---分组号" + c.Key);
                    //g代表每个小组c中的pig对象
                    c.ToList().ForEach(g => Console.WriteLine(g.ToString1()));
                });
            }

**9.Linq**

static void C1001Where()
            {
                var list = GetPigeList();
                var nlist1 = (from c in list where c.Age > 5 select c).ToList();
    
            }
            static void C1002Sort()
            {
                var list = GetPigeList();
                var orderList = (from c in list orderby c.Age descending select new { c.Name,c.Age}).ToList();
            }
            static void C1003LinqJoin()
            {
                var piglist = GetPigeList();
                var pigTypeList = GetPigeTypeList();
                var nlist = (from c in piglist
                             join t in pigTypeList
                             on c.TypeID equals t.TypeID
                             select new { c.Name, c.ID, t.TName }).ToList();
    
            }
            static void C1004GroupBy()
            {
                var list = GetPigeList();
                (from c in list group c by c.TypeID).ToList();
            }

准备两个集合，两个类，和一个扩展方法

public static List<Pig> GetPigeList()
            {
                return new List<Pig>
                {
                    new Pig() {TypeID=1,ID=1,Name="八戒",Age=500 },
                    new Pig() {TypeID=2,ID=2,Name="八戒1",Age=5 },
                    new Pig() {TypeID=3,ID=3,Name="小猪",Age=1 },
                    new Pig() {TypeID=2,ID=4,Name="老猪",Age=5},
                };
            }
            public static List<PigType> GetPigeTypeList()
            {
                return new List<PigType>
                {
                    new PigType() {TypeID=1,TName="土猪" },
                    new PigType() {TypeID=2,TName="野猪" },
                    new PigType() {TypeID=3,TName="家猪" }
                };
            }

public class Pig
        {
            public int TypeID { get; set; }
            public int ID { get; set; }
            public string Name { get; set; }
            public int Age { get; set; }
        }
        public class PigType
        {
            public int TypeID { get; set; }
            public string TName { get; set; }
        }
        public static class ExPig
        {
            public static string ToString1(this Pig pig)
            {
                return "猪ID：" + pig.ID + " 猪名：" + pig.Name + " 猪龄：" + pig.Age;
            }
        }