C#委托学习 原文推荐：http://www.cnblogs.com/warensoft/archive/2010/03/19/1689806.html?login=1#commentform

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.IO;
using System.Data.SqlClient;

namespace WindowsFormsApplication1
{
    /**
     * 两个RadioButton，分别用来让用户选择求最大值以及求最小值  rbtMax、rbtMin

    二个TextBox，用来输入两个操作数   tbxOP1/tbxOP2

    一个TextBox，用来显示运算结果   tbxResult

    一个Button，用来执行运算  btGetResult
    *
    **/

    public partial class FrmEventHandle : Form
    {

        delegate int MyDelegate(int a, int b);
        MyDelegate md = null;

        public FrmEventHandle()
        {
            InitializeComponent();
        }

        int Max(int a, int b)
        {
            return a > b ? a : b;
        }
        int Min(int a, int b)
        {
            return a < b ? a : b;
        }

        private void rbtMax_CheckedChanged(object sender, EventArgs e)
        {
            if (rbtMax.Checked == true)
            {
                this.md = new MyDelegate(this.Max);
            }
        }

        private void rbtMin_CheckedChanged(object sender, EventArgs e)
        {
            if (rbtMin.Checked == true)
            {
                this.md = new MyDelegate(this.Min);
            }
        }
        /// <summary>
        /// btnClick事件
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void btGetResult_Click(object sender, EventArgs e)
        {
            if (this.md == null)
            {
                MessageBox.Show("委托md没有指向任何方法！");
                return;
            }
            int a = int.Parse(this.tbxOP1.Text);
            int b = int.Parse(this.tbxOP2.Text);
            //int c = this.md(a, b);
            int c = this.md.Invoke(a,b);
            this.tbxResult.Text = c.ToString();
        }
        /// <summary>
        /// 窗体加载
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void FrmEventHandle_Load(object sender, EventArgs e)
        {
            this.md = new MyDelegate(this.Max);
        }

        ///
        /// 生成一个委托,用于实现多播操作
        ///
        /// 文件的原始路径
        delegate void MyMulticastDelegate(string path);

        ///
        /// 用于生成日志文档
        ///
        /// 文件的原始路径
        static void CreateLogFile(string originalPath)
        {

            if (!Directory.Exists("log"))
            {
                Directory.CreateDirectory("log");
            }

            StreamWriter sw = new StreamWriter("log/log.txt", true);
            sw.WriteLine("新文件已经创建，创建时间：{0}，文件路径：{1}", DateTime.Now.ToLongTimeString(), originalPath);
            sw.Close();

            Console.WriteLine("已经写入日志！");

        }

        ///
        /// 用于将文件写入数据库
        ///
        /// 文件的原始路径
        static void WriteToDb(string originalPath)
        {

            FileStream fs = new FileStream(originalPath, FileMode.Open);

            var buffer = new byte[fs.Length];

            fs.Read(buffer, 0, buffer.Length);

            fs.Close();

 

            SqlConnection con = new SqlConnection("server=.;database=test;uid=sa;pwd=sasa");

            SqlCommand cmd = con.CreateCommand();

            cmd.CommandText = "insert into tb_files values(@ID,@FileName,@CreationTime,@FileBytes)";

            cmd.Parameters.Add("@ID", SqlDbType.UniqueIdentifier).Value = Guid.NewGuid();

            cmd.Parameters.Add("@CreationTime", SqlDbType.DateTime).Value = DateTime.Now;

            cmd.Parameters.Add("@FileName", SqlDbType.NText).Value = Path.GetFileName(originalPath);

            cmd.Parameters.Add("@FileBytes", SqlDbType.Image).Value = buffer;
            con.Open();
            cmd.ExecuteNonQuery();
            con.Close();
            Console.WriteLine("已经写入数据库");

        }

        private void button1_Click(object sender, EventArgs e)
        {
            //创建原始文件
            StreamWriter sw = new StreamWriter("new file.txt", false);
            sw.WriteLine("this is a new file");
            sw.Close();

            //创建委托,并指向CreateLogFile方法
            MyMulticastDelegate logDelegate = new MyMulticastDelegate(CreateLogFile);
            //创建委托,并指向WriteToDb方法
            MyMulticastDelegate dbDelagate = new MyMulticastDelegate(WriteToDb);
            MyMulticastDelegate multicastDelegate = logDelegate;
            //在多播委托的调用链中添加新的委托元素
            multicastDelegate = multicastDelegate + dbDelagate;
            //调用多播委托,并且序列执行两个委托所指向的方法
            multicastDelegate("new file.txt");
        }
    }
}