原文链接

Unity C# 多态 委托 事件 匿名委托 Lambda表达式 观察者模式 .NET 框架中的委托和事件 | Jason_c

原文写得很好，但是主题格式我不太喜欢，所以我对文章的格式进行了修整，方便自己日后阅读

正文

二、委托

委托：将方法作为参数传递。

using System;

namespace Delegate
{
    public delegate void GreetingDelegate(string name);

    class People
    {
        public static void Speak(string name,GreetingDelegate _delegate)
        {
            _delegate (name);
        }
    }
    class Language
    {
        public static void EnglishGreeting(string name)
        {
            Console.WriteLine ("Good Morning,"+name);
        }
        public static void ChineseGreeting(string name)
        {
            Console.WriteLine ("早上好，"+name);
        }
    }

    class MainClass
    {
        public static void Main (string[] args)
        {
            GreetingDelegate greetingDelegate;
            greetingDelegate = Language.EnglishGreeting ;//委托第一次绑定时，须用“=”
            People.Speak("Jason", greetingDelegate);
            greetingDelegate -= Language.EnglishGreeting;
            greetingDelegate += Language.ChineseGreeting ;
            People.Speak("杰森", greetingDelegate);
        }
    }
}

• 运行结果

三、事件

事件：对委托类型的变量的封装；

在类的内部，不管你声明的事件是 public 还是 protected ，它总是 private 的；

在类的外部，注册 += 和注销 -= 的访问限定符与你在 声明事件 时使用的访问符相同。

using System;

namespace Delegate
{
    public delegate void GreetingDelegate(string name);

    class People
    {
        public static event GreetingDelegate greetingEvent;
        public static void Speak(string name)
        {
            greetingEvent(name);
        }
    }
    class Language
    {
        public static void EnglishGreeting(string name)
        {
            Console.WriteLine ("Good Morning,"+name);
        }
        public static void ChineseGreeting(string name)
        {
            Console.WriteLine ("早上好，"+name);
        }
    }

    class MainClass
    {
        public static void Main (string[] args)
        {
            People.greetingEvent += Language.EnglishGreeting;
            People.Speak ("Jason");
            People.greetingEvent -= Language.EnglishGreeting;
            People.greetingEvent += Language.ChineseGreeting;
            People.Speak ("杰森");
        }
    }
}

• 运行结果

四、匿名委托

匿名委托：也叫匿名方法，将代码块当做参数传递，因为不需要创建单独的方法，因此 减少了实例化委托所需要的开销 ；

using System;

namespace Delegate
{
    public delegate void GreetingDelegate(string name);
    class People
    {
        public static void Speak(string name,GreetingDelegate _delegate)
        {
            _delegate (name);
        }
    }

    class MainClass
    {
        public static void Main (string[] args)
        {
            GreetingDelegate greetingDelegate = delegate(string name) {
                Console.WriteLine ("Good Morning,"+name);
            };
            People.Speak ("Jason",greetingDelegate);

            GreetingDelegate greetingDelegate_1 = delegate(string name) {
                Console.WriteLine ("早上好,"+name);
            };
            People.Speak ("杰森",greetingDelegate_1);
        }
    }
}

在使用匿名方法时候，要 注意

• 不能使用跳转语句跳转到该匿名方法的外部，
• 同样不能用跳转语句从外部跳转到匿名方法内部，
• 匿名方法中不能访问不安全代码（unsafe），
• 也不能访问在匿名方法外部使用的 ref 和 out 参数。

在实际问题中可能遇到的问题要比上面的代码复杂得多，在匿名方法中捕获变量就是难点之一。

• 运行结果：

五、Lambda 表达式

Lambda 表达式：比匿名委托代码更加简洁，运算符 ()=>,

using System;

namespace Delegate
{
    public delegate void GreetingDelegate(string name);
    class People
    {
        public static void Speak(string name,GreetingDelegate _delegate)
        {
            _delegate (name);
        }
    }

    class MainClass
    {
        public static void Main (string[] args)
        {
            GreetingDelegate greetingDelegate = (string name) =>
                Console.WriteLine ("Good Morning,"+name);
            People.Speak ("Jason",greetingDelegate);

            GreetingDelegate greetingDelegate_1 = (string name) => {
                Console.WriteLine ("早上好," + name);
            };
            People.Speak ("杰森",greetingDelegate_1);
        }
    }
}

• 运行结果：