Delegate, Method as Parameter.

Posted 2020-07-04 许明会的计算机技术主页

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代理, 将方法作为另一方法的参数. 类似C里面的函数指针.

using System;
using System.Windows.Forms;
using System.Threading;

namespace Demo
{
    public delegate void Greeting(string name);

    public class Demo
    {
        private static void GreetingEnglish(string name)
        {
            Console.WriteLine ("Hello,{0}", name);
        }
        private static void GreetingChinese(string name)
        {
            Console.WriteLine ("你好,{0}", name);
        }
        //委托,将方法作为另一方法的参数.委托可以代表一系列返回值和参数类型与其一致的方法.
        private static void GreetingPeople(string name, Greeting greet)
        {
            greet (name);
        }
            
        public static void Main()
        {
            GreetingPeople ("Jeffrey Richter", GreetingEnglish);
            GreetingPeople ("刘德华", GreetingChinese);
            Console.ReadKey ();
        }
    }

}

将方法绑定到委托

using System;
using System.Threading;

namespace Demo
{
    public delegate void Greeting(string name);

    public class Demo
    {
        private static void GreetingEnglish(string name)
        {
            Console.WriteLine ("Hello,{0}", name);
        }
        private static void GreetingChinese(string name)
        {
            Console.WriteLine ("你好,{0}", name);
        }
        private static void GreetingFrance(string nom)
        {
            Console.WriteLine ("Bonjour,{0}", nom);
        }
        //delegate: use the Method name as Parameters.
        private static void GreetingPeople(string name, Greeting greet)
        {
            greet (name);
        }
            
        public static void Main()
        {
            GreetingPeople ("Jeffrey Richter", GreetingEnglish);
            GreetingPeople ("刘德华", GreetingChinese);
            //bind Method to Delegate
            Greeting chinese = GreetingChinese;
            Greeting english = GreetingEnglish;
            english += GreetingFrance;
            chinese ("许明会");
            english ("Matt Petrek");
            Console.ReadKey ();
        }
    }
}

委托与接口

using System;
using System.Threading;

namespace Demo
{
    interface IGreeting{
        void Greeting(string name);
    };

    public class GreetingChinese:IGreeting
    {
        public void Greeting(string name)
        {
            Console.WriteLine ("你好，{0}", name);
        }
    }    
    public class GreetingEnglish:IGreeting
    {
        public void Greeting(string name)
        {
            Console.WriteLine ("Hello,{0}", name);
        }
    }
    public class Demo
    {
        private static void Greeting(string name, IGreeting greeting)
        {
            greeting.Greeting (name);
        }
        public static void Main()
        {
            IGreeting chinese = new GreetingChinese ();
            IGreeting english = new GreetingEnglish ();
            chinese.Greeting ("许明会");
            english.Greeting ("Jeffrey Richter");
            Greeting ("Matt Petrik", english);
            Console.ReadKey ();
        }
    }
}

更好的封装，事件的由来

using System;
using System.Threading;

namespace Demo
{
    public delegate void Greet(string name);

    public class GreetingManager
    {
        public Greet deleGreet;
        public void Greeting(string name, Greet greet)
        {
            greet (name);
        }
    }

    public class Demo
    {
        private static void GreetingEnglish(string name)
        {
            Console.WriteLine ("Hello,{0}", name);
        }
        private static void GreetingChinese(string name)
        {
            Console.WriteLine ("你好,{0}", name);
        }

        //Main()
        public static void Main()
        {
            GreetingManager gm = new GreetingManager ();
            gm.deleGreet = GreetingChinese;
            gm.deleGreet += GreetingEnglish ;
            gm.Greeting ("Matt Petrik",gm.deleGreet);
            Console.ReadKey ();
        }
    }
}

更好的封装，准备引入事件

using System;
using System.Threading;

namespace Demo
{
    public delegate void Greet(string name);

    public class GreetingManager
    {
        public Greet deleGreet;

        public void Greeting(string name)
        {
            if (deleGreet!=null) {
                deleGreet(name);
            }
        }
    }

    public class Demo
    {
        private static void GreetingEnglish(string name)
        {
            Console.WriteLine ("Hello,{0}", name);
        }
        private static void GreetingChinese(string name)
        {
            Console.WriteLine ("你好,{0}", name);
        }

        //Main()
        public static void Main()
        {
            GreetingManager gm = new GreetingManager ();
            gm.deleGreet = GreetingChinese;
            gm.deleGreet += GreetingEnglish ;
            gm.Greeting ("Matt Petrik");
            Console.ReadKey ();
        }
    }
}

委托的目的是把它暴露到外面，以让客户端进行方法注册。Event保证在类的内部总是Private，可认为是为Delegate定制的Property。

using System;
using System.Threading;

namespace Demo
{
    public delegate void Greet(string name);

    public class GreetingManager
    {
        //public Greet deleGreet;
        public event Greet EventGreet;

        public void Greeting(string name)
        {
            if (EventGreet!=null) 
                EventGreet(name);
        }
    }

    public class Demo
    {
        private static void GreetingEnglish(string name)
        {
            Console.WriteLine ("Hello,{0}", name);
        }
        private static void GreetingChinese(string name)
        {
            Console.WriteLine ("你好,{0}", name);
        }

        //Main()
        public static void Main()
        {
            GreetingManager gm = new GreetingManager ();
            gm.EventGreet += GreetingChinese;
            gm.EventGreet += GreetingEnglish ;
            //Greeting call from client, that‘s not good!
            gm.Greeting ("Matt Petrik");
            Console.ReadKey ();
        }
    }
}

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的

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