委托和事件

1.委托

　　1）委托类型是用户自定义类型   比作MyClass类型

　　2）委托存储的就是一系列具有相同签名和返回回类型的方法的地址  比作MyClass 类型 的变量存储的是对象的地址。

　　问题1：为什么使用委托？

　　回复：每种交通工具 的发动机都不一样，你不可能为每个交通工具的构造函数设置各种不同的发动机类，但是如果我们

　　用委托作为入参，指向发动的方法，那么客户端在调用时只关注发动的方法，不必关注哪种发动机。

    public class Program
    {
        //定义委托类型
        public delegate void DPrint(string msg);
        static void Main(string[] args)
        {
            DPrint Print;//声明一个委托
            Print = Program.Print;//赋值委托 指定一个对象的函数的指针
            Print += Program.PrintLine;//组合委托
            Print("msg");//委托调用

            DPrint myPrint = delegate(string msg)//委托指向匿名方法
            {
                Console.WriteLine("myPrint:"+msg);
            };
            myPrint("msg1");

            DPrint lambdaPrint = (string msg) =>//Lambda表达式:简化匿名方法
            {
                Console.WriteLine("lambdaPrint:" + msg);
            };
            lambdaPrint("msg2");
            Console.ReadLine();
        }
        public static void Print(string msg)
        {
            Console.WriteLine("Print:" + msg);
        }
        public static void PrintLine(string msg)
        {
            Console.WriteLine("PrintLine:" + msg);
        }
    }

 　　使用委托前的代码：

    public class Car
    {
        public Car(CarMove dMove)
        {
         
        }
    }

    public class Bicycle
    {
        public Bicycle(BicycleMove dMove)
        {
           
        }
    }
    public class BicycleMove
    {
        public BicycleMove()
        {
            Console.WriteLine("BicycleMove");
        }
    }
    public class CarMove
    {
        public CarMove()
        {
            Console.WriteLine("CarMove");
        }
    }
    public class Program
    {

        static void Main(string[] args)
        {
            new Car(new CarMove());//new Car(new BicycleMove());
            Console.ReadLine();
        }

    }

　     使用委托后的代码：

    public delegate void DMove();
    public class Car
    {
        public Car(DMove dMove)
        {
            dMove();
        }
    }

    public class Bicycle
    {
        public Bicycle(DMove dMove)
        {
            dMove();
        }
    }
    public class Program
    {

        static void Main(string[] args)
        {
            new Car(Program.BicycleMove);
            Console.ReadLine();
        }

        public static void CarMove()
        {
            Console.WriteLine("CarMove");
        }
        public static void BicycleMove()
        {
            Console.WriteLine("BicycleMove");
        }
    }

2.事件　　

    /// <summary>
    /// 事件发送方和接收的数据信使
    /// </summary>
    public class Extra : EventArgs
    {
        public string Note { get; set; }
    }

    /// <summary>
    /// 事件发送方
    /// </summary>
    public class Reader
    {
        public delegate void LookDelegate(object sender, Extra eventArgs);
        public event LookDelegate LookEvent;
        public void Read(Extra bookEventArgs)
        {
            LookEvent(this, bookEventArgs);
        }
    }

    /// <summary>
    /// 事件接收方
    /// </summary>
    public class Writer
    {
        public Writer(Reader reader)
        {
            reader.LookEvent += new Reader.LookDelegate(this.Write);
        }
        public void Write(object sender, Extra bookEventArgs)
        {
            Console.Write("Write:" + bookEventArgs.Note);
        }
    }

    public class LineWriter
    {
        public LineWriter(Reader reader)
        {
            reader.LookEvent += new Reader.LookDelegate(this.WriteLine);
        }
        public void WriteLine(object sender, Extra bookEventArgs)
        {
            Console.WriteLine("WriteLine:" + bookEventArgs.Note);
        }
    }

            Extra book = new Extra { Note = "aaa" };
            Reader reader = new Reader();
            LineWriter LineWriter = new LineWriter(reader);
            Writer writer = new Writer(reader);           
            reader.Read(book);
            Console.ReadLine();