委托

对函数类型的封装，相当于函数指针

Action,Func

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using System;
delegate double Fun( double x );
public class DelegateIntegral
{
    public static void Main()
    {
        Fun fun = new Fun(Math.Sin);
        double d = Integral( fun, 0, Math.PI/2, 1e-4 ); 
        Console.WriteLine( d );
 
        Fun fun2 = new Fun( Linear );
        double d2 = Integral( fun2, 0, 2, 1e-3 );
        Console.WriteLine( d2 );
 
        Rnd rnd = new Rnd();
        double d3 = Integral( new Fun(rnd.Num), 0, 1, 0.01 ); 
        Console.WriteLine( d3 );
    }
    static double Linear( double a )
    {
        return a*2+1;
    } 
    class Rnd 
    {
        Random r = new Random();
        public double Num( double  x )
        {
            return r.NextDouble();
        }
    }
    static double Integral(Fun f, double a, double b, double eps)// 积分计算
    {
        int n,k;
        double fa,fb,h,t1,p,s,x,t=0;
 
        fa=f(a); 
        fb=f(b);
 
        // 迭代初值
        n=1; 
        h=b-a;
        t1=h*(fa+fb)/2.0;
        p=double.MaxValue;
 
        // 迭代计算
        while (p>=eps)
        { 
            s=0.0;
            for (k=0;k<=n-1;k++)
            { 
                x=a+(k+0.5)*h;
                s=s+f(x);
            }
 
            t=(t1+h*s)/2.0;
            p=Math.Abs(t1-t);
            t1=t; 
            n=n+n; 
            h=h/2.0;
        }
        return t;
    }
}

事件

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using System;
public delegate void DownloadStartHandler(object sender, DownloadStartEventArgs e);  //声明委托
public delegate void DownloadEndHandler(object sender, DownloadEndEventArgs e);  
public delegate void DownloadingHandler(object sender, DownloadingEventArgs e);  
public class DownloadStartEventArgs
{
    public string Url{ get{ return _url;} set{ _url=value;} }
    private string _url;
  
    public DownloadStartEventArgs( string url ){ this._url = url; }
}
public class DownloadEndEventArgs
{
    public string Url{ get{ return _url;} set{ _url=value;} }
    private string _url;
  
    public long ByteCount { get { return _byteCount; } set{ _byteCount=value;} }
    private long _byteCount;
  
    public DownloadEndEventArgs( string url, long size  ){ this._url = url; this._byteCount=size; }
}
public class DownloadingEventArgs
{
    public string Url{ get{ return _url;} set{ _url=value;} }
    private string _url;
  
    public double Percent { get { return _percent; } set{ _percent=value;} }
    private double _percent;
  
    public DownloadingEventArgs( string url, double percent  ){ this._url = url; this._percent=percent; }
}
public class Crawler
{
  
    public event DownloadStartHandler DownloadStart;  // 声明事件
    public event DownloadEndHandler DownloadEnd;  // 声明事件
    public event DownloadingHandler Downloading;  // 声明事件
    public string Name { get{return name;} set{ name=value;} }
    private string name;
    private string site;
    public Crawler( string name, string site )
    {
        this.name = name;
        this.site = site;
    }
    public void Craw()
    {   
        while( true )
        {
            string url = GetNextUrl();
            if( url == null ) break;
            long size = GetSizeOfUrl( url );
  
            if( DownloadStart != null ) //下载开始的事件发生
            {
                DownloadStart( this, new DownloadStartEventArgs(url));
            }
              
            for( long i=0; i<size+1024; i+=1024 )
            {
                //下载数据。。。
                System.Threading.Thread.Sleep( 100 );
                double percent = (int)(i*100.0/size);
                if( percent>100) percent=100;
                  
                if( Downloading != null ) //下载数据的事件发生
                {
                    Downloading( this, new DownloadingEventArgs(url, percent));
                }
            }
  
            if( DownloadEnd != null ) //下载结束的事件发生
            {
                DownloadEnd( this, new DownloadEndEventArgs(url, size));
            }
        }
  
    }
    private string GetNextUrl()
    {
        int a = rnd.Next(10);
        if( a == 0 ) return null;
        return site + "/Page" + a + ".htm";
    }
    private long GetSizeOfUrl( string url)
    {
        return rnd.Next(3000 * url.Length);
    }
    private Random rnd = new Random();
}
class Test
{
    static void Main()
    {
        Crawler crawler = new Crawler("Crawer101", "http://www.pku.edu.cn");
  
        crawler.DownloadStart += new DownloadStartHandler( ShowStart ); //注册事件
        crawler.DownloadEnd += new DownloadEndHandler( ShowEnd );
        crawler.Downloading += new DownloadingHandler( ShowPercent );
          
          
        crawler.Craw();
    }
    static void ShowStart(object sender, DownloadStartEventArgs e){
        Console.WriteLine( (sender as Crawler).Name + "开始下载" + e.Url );
    }
    static void ShowEnd(object sender, DownloadEndEventArgs e){
        Console.WriteLine( "\n\r下载" + e.Url + "结束,其下载" + e.ByteCount + "字节" );
    }
    static void ShowPercent(object sender, DownloadingEventArgs e){
        Console.Write( "\r下载" + e.Url + "......." + e.Percent + "%" );
          
    }
}

匿名函数

Lambda

Linq

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using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
  
using System.Threading;
  
namespace MethodDelegateLamda
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
  
        //示例1,使用线程
        private void button1_Click(object sender, EventArgs e)
        {
            //csharp 1.0
            //使用委托，使用已定义好的函数
            new Thread(new ThreadStart(MyFun)).Start();
  
            //csharp 2.0
            //省略委托：MyFun自动实例化为ThreadStart委托（
            new Thread(MyFun).Start();
            //匿名方法
            new Thread(new ThreadStart( delegate(){ Console.Write("my function"); })).Start();
            //匿名方法，省略参数列表
            new Thread(new ThreadStart( delegate{ Console.Write("my function"); })).Start();
            //匿名方法，自动转委托
            new Thread( delegate(){ Console.Write("my function"); }).Start(); 
  
            //csharp 3.0
            //Lambda表达式
            new Thread(() => { Console.Write("my function"); }).Start();
  
        }
  
        void MyFun()
        {
            Console.Write("my function");
        }
  
        //示例2,使用事件
  
        private void button3_Click(object sender, EventArgs e)
        {
            Example3();
        }
        void Example3()
        {
            //csharp 1.0
            //使用委托，使用自定义函数
            this.MouseMove += new MouseEventHandler(Form1_MouseMove);
  
            //csharp 2.0
            //自动转委托
            this.MouseMove += Form1_MouseMove; 
  
            Label lbl = this.label1; //这个变量下面使用了闭包（简单地说，使用外部的局部变量）
            this.MouseMove += new MouseEventHandler(delegate(object sender, MouseEventArgs e) { lbl.Text = e.X + "," + e.Y; });
            this.MouseMove += delegate(object sender, MouseEventArgs e) { lbl.Text = e.X + "," + e.Y; };
  
            //csharp 3.0 
            //使用Lambda表达式
            this.MouseMove += (object sender, MouseEventArgs e) => { lbl.Text = e.X + "," + e.Y; };　//Lamda
            this.MouseMove += (sender, e) => { lbl.Text = e.X + "," + e.Y; }; //可以省略类型
        }
  
        void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            this.label1.Text = e.X + "," + e.Y;
        }
  
        //示例3, 数组排序
        class Book
        {
            public string title;
            public double price;
            public Book(string title, double price) { this.title=title; this.price=price; }
        }
        private void button2_Click(object sender, EventArgs e)
        {
            Random rnd = new Random();
            Book [] books  = new Book[ 10];
            for( int i=0; i<books.Length; i++ ) books[i] = new Book( "Book"+i, rnd.Next(100) );
  
            //csharp 1.0
            Array.Sort(books, new MyComparer()); //用一个IComparer
  
            //csharp 2.0
            Array.Sort<Book>(books, new Comparison<Book>(delegate(Book book1, Book book2) { return (int)(book1.price - book2.price); })); //使用Comparison委托
            Array.Sort<Book>(books, delegate(Book book1, Book book2) { return (int)(book1.price - book2.price); });
  
            //csharp 3.0
            Array.Sort<Book>(books, (Book book1, Book book2) => (int)(book1.price - book2.price));
            Array.Sort<Book>(books, (book1, book2) => (int)(book1.price - book2.price)); //省略参数类型
  
            //使用Linq
            IOrderedEnumerable<Book> result = from book in books orderby book.price select book;
  
            var result2 = from book in books  where book.price>=0 orderby book.price select book.title;
            foreach (string s in result2) Console.Write(s);
  
            var result3 = books
                .Where<Book>(b => b.price>=0)
                .OrderBy<Book, double>(b => b.price, Comparer<double>.Default)
                .Select<Book,Book>(book => book);
            foreach (Book b in result3) Console.Write(b.price+" ");
       }
        class MyComparer : System.Collections.IComparer
        {
            public int Compare(object x1, object x2)
            {
                return (int)(((Book)x1).price - ((Book)x2).price);
            }
        }
    }
}