C# 委托和泛型委托示例

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
 
namespace ConsoleApp6
{
    class Program
    {
        public delegate void SaySomething(string name); //定义委托
        public static event SaySomething peopleCome; //定义事件 关注SaySomething委托，当事件发生的时候，会通知关注的“委托”（再由这些“委托”去调用具体的方法）。
 
        private delegate double DoCallFunc(double num1, double num2);
 
        static void Main(string[] args)
        {
            peopleCome += SayHello;  //注册方法到事件上
            peopleCome += SayNiceToMeetYou; //注册方法到事件上
            peopleCome += SayGoodbye; //注册方法到事件上
            peopleCome("张三");  //绑定触发事件
 
            Console.WriteLine("=====================================");
 
            int x = 10;
            int y = 3;
            // DoCallFunc md = new DoCallFunc(Add);
 
            DoCallFunc df;
            df = Add;
            Console.WriteLine("callFunc：{0}", df(x, y));
            df = Sub;
            Console.WriteLine("callFunc：{0}", df(x, y));
            df = Multiply;
            Console.WriteLine("callFunc：{0}", df(x, y));
            df = Divide;
            Console.WriteLine("callFunc：{0}", df(x, y));
 
 
            Console.WriteLine("=====================================");
            Console.WriteLine("callFunc：{0}", Calculate(x, y, Add));
            Console.WriteLine("callFunc：{0}", Calculate(x, y, Sub));
            Console.WriteLine("callFunc：{0}", Calculate(x, y, Multiply));
            Console.WriteLine("callFunc：{0}", Calculate(x, y, Divide));
 
            Console.ReadKey();
        }
 
        #region 普通委托
        private static double Calculate2(double num1, double num2, DoCallFunc doCallFunc)
        {
            return doCallFunc(num1, num2);
        }
        #endregion
 
        #region 泛型委托
 
        /*
            泛型Action<T>委托表示引用一个void返回类型的方法。Action<T>委托类存在不同的变体，可以传递至多16种不同的参数类型，
            没有泛型参数的Action类可以调用没有参数的方法。
            例如：Action<in T1>调用带一个参数的方法，Action<in T1,in T2>调用带两个参数的方法等
    　　              Func<T>的用法和Action<T>用法类似，但是Func<T>表示引用一个带返回类型的方法，
            Func<T>也存在不同的变体，至多可以传递16个参数类型和1个返回类型，
            例如：Func<in T1,out Resout>表示带一个参数的方法，Func<in T1,in T2,out Resout>表示调用带两个参数的方法。
        */
        private static double Calculate(double num1, double num2, Func<double, double, double> callFunc)
        {
            return callFunc(num1, num2);
        }
        #endregion
 
        #region 数字的加减乘除
        private static double Add(double num1, double num2)
        {
            Console.WriteLine("{0} + {1} = {2}", num1, num2, num1 + num2);
            return num1 + num2;
        }
        private static double Sub(double num1, double num2)
        {
            Console.WriteLine("{0} - {1} = {2}", num1, num2, num1 - num2);
            return num1 - num2;
        }
 
        private static double Multiply(double num1, double num2)
        {
            Console.WriteLine("{0} * {1} = {2}", num1, num2, num1 * num2);
            return num1 * num2;
        }
 
        private static double Divide(double num1, double num2)
        {
            Console.WriteLine("{0} / {1} = {2}", num1, num2, num1 / num2);
            return Math.Round(num1 / num2, 2, MidpointRounding.AwayFromZero);  //4舍5入
        }
        #endregion
 
        #region 测试
        public static void SayHello(string name) { Console.WriteLine("Hello," + name + "!"); }
 
        public static void SayNiceToMeetYou(string name) { Console.WriteLine("Nice to meet you," + name + "!"); }
 
        public static void SayGoodbye(string name) { Console.WriteLine("Bye bye," + name + "!"); }
        #endregion
    }
}