using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace PlugDemo
{
    public interface IPlugToText
    {
        string ProccessText(string text);
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace PlugDemo
{
    public class MenuNameAttribute:Attribute
    {
        private string _name;

        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }

        public MenuNameAttribute(string name)
        {
            this._name = name;
        }

    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ComPlugDemo
{
    [PlugDemo.MenuName("转小写")]
    public class PlugToLower : PlugDemo.IPlugToText
    {
        #region IPlugToText 成员
        
        public string ProccessText(string text)
        {
            return text.ToLower();
        }

        #endregion
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ComPlugDemo
{
    [PlugDemo.MenuName("转大写")]
    public class PlugToUpper:PlugDemo.IPlugToText
    {

        #region IPlugToText 成员
        
        public string ProccessText(string text)
        {
            return text.ToUpper();
        }

        #endregion
    }
}

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.Reflection;
using System.IO;
using PlugDemo;


namespace 插件Demo
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            AddPlugMenu();
        }

        void AddPlugMenu()
        {
            //1、加载正在运行的程序集的物理路径
            Assembly ass = this.GetType().Assembly;

            string location = ass.Location;

            //2、获取 程序集所在文件夹，并转成 插件程序集文件夹的路径
            string assDir = Path.GetDirectoryName(location);

            string plugDir = assDir + "\\plugs";

            //3、扫描 产检文件夹里的 所有程序集文件
            string [] dllPaths = Directory.GetFiles(plugDir,"*.dll");

            //重点： 获取插件接口 类型对象

            //4、遍历程序集文件路径，并加载程序家到内存中
            Type iplugType = typeof(IPlugToText);

            foreach (string dllPath in dllPaths)
            {
                //4.1 、根据路径 加载程序集文件 到内存中
                Assembly amy = Assembly.LoadFrom(dllPath);

                //4.2 、判断程序集中是否有插件类
                //4.2.1、获取插件程序集里公有的类
                Type[] types = amy.GetExportedTypes();
                //4.2.2 循环遍历 插件程序集里的类型 ，判断是否实现记事本插件接口
                foreach (Type t in types)
                {
                    //判断 t 是否 实现了接口 IPlugToUpper
                    if (iplugType.IsAssignableFrom(t))
                    {
                        //重要，获取的MenuNameAttribute 特性对象，或将 内部的Name现在到菜单中
                        object[] atts = t.GetCustomAttributes(typeof(MenuNameAttribute),false);
                        MenuNameAttribute menuName = atts[0] as MenuNameAttribute;

                        //重要：根据插件类型，创建 插件类 对象
                        IPlugToText iplug = Activator.CreateInstance(t) as IPlugToText;

                        ToolStripMenuItem item = new ToolStripMenuItem(menuName.Name);

                        plugMenu.DropDownItems.Add(item);

                        item.Click += new EventHandler(item_Click);

                        item.Tag = iplug;
                    } 
                }
            }
            
        }

        void item_Click(object sender, EventArgs e)
        {
            ToolStripMenuItem item = sender as ToolStripMenuItem;

            IPlugToText iplug = item.Tag as IPlugToText;
            textBox1.Text = iplug.ProccessText(textBox1.Text);
        }
    }
}