using IExtendServices;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace 插件的简单原理
{
    public class ExtendServices
    {
        private MenuStrip ms = null;
        private RichTextBox txt = null;
        public ExtendServices(MenuStrip ms, RichTextBox txt)
        {
            this.ms = ms;
            this.txt = txt;
        }
        public void Service()
        {
            string[] plugFilesPath = Directory.GetFiles(Path.Combine(Application.StartupPath, "plugs"), "*.dll");

            foreach (string itemPath in plugFilesPath)
            {
                Assembly ass = Assembly.LoadFrom(itemPath);
                //获取所有的公共类型
                Type[] assTypes = ass.GetExportedTypes();
                //自定义的接口类型
                Type itype = typeof(IExtendService);
                foreach (Type itemtype in assTypes)
                {
                    if (itemtype.IsPublic && itype.IsAssignableFrom(itemtype) && !itemtype.IsAbstract&&!itemtype.IsInterface)
                    {
                        IExtendService service = (IExtendService)Activator.CreateInstance(itemtype);
                        ToolStripMenuItem editItem = (ToolStripMenuItem)ms.Items[1];

                        ToolStripItem seritem = editItem.DropDownItems.Add(service.Name);
                        seritem.Tag = service;
                        seritem.Click += SerItemMethod;
                    }
                }

            }
        }

        private void SerItemMethod(object sender, EventArgs e)
        {
            ToolStripItem service = (ToolStripItem)sender;
            ((IExtendService)service.Tag).Service(txt);
        }
    }
}

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

namespace CNotePadPlugs
{
    public class ToASCII:IExtendServices.IExtendService
    {
        public string Name
        {
            get { return "ToASCII"; }
        }

        public void Service(System.Windows.Forms.RichTextBox txt)
        {

            string all = txt.Text;
            string txtSelected = txt.SelectedText;

            if (txtSelected == "")
                txtSelected = all;
            
            int index = txt.SelectionStart;//2
            if (index == all.Length)
                index = 0;
            //0
            string start = all.Substring(0, index);//2
            //1
            string upper = all.Substring(index, txtSelected.Length);
            char[] chars = upper.ToCharArray();
            upper = "";
            foreach (char item in chars)
            {
                upper += (int)item;
            }
            //2
            string end = txt.Text.Substring(index + txtSelected.Length);

            txt.Text = start + upper + end;    

        }
    }
}

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

namespace IExtendServices
{
    public interface IExtendService
    {
        string Name
        {
            get;
        }
        void Service(System.Windows.Forms.RichTextBox txt);
    }
}