1 using System;
  2 using System.Collections.Generic;
  3 using System.Linq;
  4 using System.Text;
  5 using System.Threading.Tasks;
  6 
  7 namespace ConsoleDemo.delegateUtil
  8 {
  9     public static class DelegateDemo
 10     {
 11         public delegate string Query(string para1, int para2);
 12 
 13         public delegate string Select(string p1, string p2, string p3, string p4, string p5, string p6,
 14             string p7, string p8, string p9, string p10, string p11, string p12,
 15             string p13, string p14, string p15, string p16, string p17, string p18);
 16 
 17         public static void Get()
 18         {
 19             Console.WriteLine("********************************");
 20 
 21             {
 22                 //.net framework 1.0
 23                 Query method = new Query(QueryUser);
 24                 var value = method.Invoke("sun", 10);
 25                 Console.WriteLine(value);//返回用户：sun, 年龄：10
 26             }
 27 
 28             {
 29                 //2.0
 30                 Query method = new Query(delegate (string para1, int para2)
 31                 {
 32 
 33                     return "返回用户：" + para1 + ", 年龄：" + para2;
 34                 });
 35 
 36                 string value = method.Invoke("sun", 20);
 37                 Console.WriteLine(value);//返回用户：sun, 年龄：20
 38             }
 39 
 40             {
 41                 //3.0
 42                 Query method = new Query((string para1, int para2) =>
 43                 {
 44                     return "返回用户：" + para1 + ", 年龄：" + para2;
 45                 });
 46                 string value = method.Invoke("sun", 30);
 47                 Console.WriteLine(value);//返回用户：sun, 年龄：30
 48             }
 49 
 50             {
 51                 //c#内置委托，带有一个string参数的，无返回值的匿名方法
 52                 Action<string> method = (string para1) =>
 53                  {
 54                      Console.WriteLine("hello " + para1 + " , age : 40");
 55                  };
 56                 method.Invoke("sun");
 57             }
 58             {
 59 
 60                 //Action 最多16个参数
 61                 Action<string, string, string, string, string,
 62                        string, string, string, string, string,
 63                        string, string, string, string, string,
 64                        string> method = (p1, p2, p3, p4, p5,
 65                                         p6, p7, p8, p9, p0,
 66                                         pq, pw, pe, pr, pp, pl) =>
 67                        {
 68                            Console.WriteLine("这里就不输出16个参数的值了");
 69                        };
 70                 method.Invoke("1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "17", "18");
 71             }
 72             {
 73 
 74                 //扩展 17个参数如何设置
 75                 //自己声明一个带有17个参数的委托
 76                 Select method = (p1, p2, p3, p4, p5,
 77                                         p6, p7, p8, p9, p10,
 78                                         p11, p12, p13, p14, p15, p16, p17, p18) =>
 79                 {
 80 
 81                     return "这里是带有18个参数的值";
 82                 };
 83                 var value = method.Invoke("1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "1", "17", "18");
 84                 Console.WriteLine(value);
 85             }
 86 
 87             {
 88                 //内置委托，有参
 89                 Func<int, string> method = (id) =>
 90                 {
 91 
 92                     return "我通过传递" + id + ",返回string的值";
 93                 };
 94                 var value = method.Invoke(50);
 95                 Console.WriteLine(value);
 96             }
 97 
 98             {
 99                 //linq
100                 User u = UserList().Find(t => t.Id == 1);
101                 Console.WriteLine("linq自带的方法：" + u.Name);
102 
103                 //自己定义一个
104                 User tmp = UserList().FindByDemo(t => t.Id == 1);
105                 Console.WriteLine("自己手写方法:" + tmp.Name);
106 
107 
108                 //思考 场景:查询语句会出现多条件的查询（面试中有被问到），如何做到不通过if else判断
109                 IEnumerable<User> list = null;
110                 List<User> datasource = UserList();
111                 if (1 == 0) //假设过滤条件为用户年纪大于20
112                 {
113                     list = datasource.Where(t => t.Age > 20);
114                 }
115 
116                 if (1 == 1) //假设过滤条件为用户名字包含i的用户
117                 {
118                     list = datasource.Where(t => t.Name.IndexOf("i") >= 0);
119                 }
120 
121                 //以上场景写法
122 
123                 //合理写法：
124 
125             }
126             {
127                 //linq to object 之IEnumerable 操作内存     使用内置委托
128                 //linq to sql    之 IQueryable 拼接sql??    表达式目录树，二叉树
129             }
130             Console.WriteLine("********************************");
131         }
132 
133 
134         private static string QueryUser(string Name, int age)
135         {
136             return "返回用户：" + Name + ", 年龄：" + age;
137         }
138 
139 
140         private static List<User> UserList()
141         {
142 
143 
144 
145             List<User> tmp = new List<User>();
146 
147             tmp.Add(new User() { Id = 1, Age = 10, Name = "sun" });
148             tmp.Add(new User() { Id = 2, Age = 20, Name = "bob" });
149             tmp.Add(new User() { Id = 3, Age = 25, Name = "justin" });
150             tmp.Add(new User() { Id = 4, Age = 30, Name = "linda" });
151             tmp.Add(new User() { Id = 5, Age = 40, Name = "lucy" });
152             tmp.Add(new User() { Id = 6, Age = 50, Name = "momo" });
153             tmp.Add(new User() { Id = 7, Age = 60, Name = "any" });
154             tmp.Add(new User() { Id = 8, Age = 70, Name = "lily" });
155 
156             return tmp;
157 
158         }
159 
160         public static T FindByDemo<T>(this List<T> list, Func<T, bool> expression) where T : class, new()
161         {
162             T t = new T();
163             foreach (var u in list)
164             {
165                 if (expression.Invoke(u))
166                 {
167                     t = u;
168                 }
169             }
170 
171             return t;
172         }
173 
174     }
175 
176     public class User
177     {
178 
179         public int Id { get; set; }
180         public int Age { get; set; }
181         public string Name { get; set; }
182     }
183 }