反射，插件接口

先創建下圖的一個窗體，插件下沒添加項目，是留給反射加載.dll插件的。在debug目錄下加一個Plugin文件夾，將插件的.dll文件放在此文件夾下可以生效。

給方案添加一個單獨的項目來寫規範插件的接口，因爲需要生成一個.dll給寫插件的人調用

接口的代碼如下：

using System.Windows.Forms;

namespace NotePad.PluginInterface
{
    public delegate TextBox GetTextBoxDelegate();
    public interface NotePadPluginInterface
    {
        //string Name { get; }

        //void Run(System.Windows.Forms.TextBox textBox);
        
        //這個接口可以只要表示插件名稱Name屬性，和功能的Run(Textbox textbox)的方法，
        //在主程序根據Name生成ToolStripMenuItem，並綁定事件，然後執行Run。
        //但是把ToolStripMenuItem給接口，插件可以實現更復雜的ToolStripMenuItem
        
        ToolStripMenuItem[] Items 
        {
            get;
            set;
        }

        TextBox textbox
        {
            get;
            set;
        }

        event GetTextBoxDelegate GetTextBoxEvent;//用來獲取當前的textbox

        void Initize();//生成ToolStripMenuItem，並綁定事件等。

    }
}

窗體加載插件的代碼

using NotePad.PluginInterface;
using System;
using System.IO;
using System.Reflection;
using System.Windows.Forms;

namespace NotePad
{
    public partial class NotePad : Form
    {
        public NotePad()
        {
            InitializeComponent();
        }
        private void NotePad_Load(object sender, EventArgs e)
        {
            string path = Assembly.GetExecutingAssembly().Location;
            string addtions = Path.Combine(Path.GetDirectoryName(path), "Plugin");
            string[] dlls = Directory.GetFiles(addtions, "*.dll");//獲取插件.dll文件
            foreach (string dll in dlls)
            {
                Assembly assenmbly = Assembly.LoadFile(dll);//加載指定路徑上的程序集文件的內容
                Type[] types = assenmbly.GetExportedTypes();//獲取此程序集中定義的Public類型
                Type typeNotePadExtInterface = typeof(NotePadPluginInterface);
                foreach (Type type in types)
                {
                    //驗證類型實現了NotePadExtInterface接口並且可以實例化
                    if (typeNotePadExtInterface.IsAssignableFrom(type) && !type.IsAbstract)
                    {
                        NotePadPluginInterface notePadEx = (NotePadPluginInterface)Activator.CreateInstance(type);//創建插件實例
                        notePadEx.Initize();//先初始化插件裏的Item
                        this.PluginToolStripMenuItem.DropDownItems.AddRange(notePadEx.Items);//將插件裏定義的Item加爲窗體 "插件"項的子項
                        notePadEx.GetTextBoxEvent += NotePadEx_GetTextBoxEvent;
                    }
                }
            }
        }

        private TextBox NotePadEx_GetTextBoxEvent()
        {
            return textBox1; 
        }
    }
}

寫插件
在插件的項目裏引用規範插件的接口的程序集

插件的代碼如下：

using NotePad.PluginInterface;
using System;
using System.Windows.Forms;

namespace NotePadPlugin
{
    public class NotePadPlugin: NotePadPluginInterface
    {
        public ToolStripMenuItem[] Items
        {
            get;
            set;
        }

        public TextBox textbox
        {
            get;
            set;
        }

        public event GetTextBoxDelegate GetTextBoxEvent;

        public void Initize()
        {
            ToolStripMenuItem switchCaseItem = new ToolStripMenuItem();
            switchCaseItem.Text = "切換大小寫";

            ToolStripMenuItem ToUpperItem = new ToolStripMenuItem();
            ToUpperItem.Text = "大寫";
            ToUpperItem.Click += ToUpperItem_Click;

            ToolStripMenuItem ToLowerItem = new ToolStripMenuItem();
            ToLowerItem.Text = "小寫";
            ToLowerItem.Click += ToLowerItem_Click;

            switchCaseItem.DropDownItems.AddRange(new ToolStripMenuItem[] { ToUpperItem, ToLowerItem });

            ToolStripMenuItem clearTextItem = new ToolStripMenuItem();
            clearTextItem.Text = "清空";
            clearTextItem.Click += ClearText_Click;

            ToolStripMenuItem colorItem = new ToolStripMenuItem();
            colorItem.Text = "顏色";
            colorItem.Click += ColorItem_Click; ;

            Items = new ToolStripMenuItem[] { switchCaseItem, clearTextItem,colorItem };
        }

        private void ColorItem_Click(object sender, EventArgs e)
        {
            textbox = GetTextBoxEvent();
            using (ColorDialog colorDialog = new ColorDialog())
            {
                if (colorDialog.ShowDialog() == DialogResult.OK)
                {
                    textbox.ForeColor = colorDialog.Color;
                }
            }
        }

        private void ClearText_Click(object sender, EventArgs e)
        {
            textbox = GetTextBoxEvent();
            textbox.Text = "";
        }

        private void ToLowerItem_Click(object sender, EventArgs e)
        {
            textbox = GetTextBoxEvent();
            textbox.Text = textbox.Text.ToLower();
        }

        private void ToUpperItem_Click(object sender, EventArgs e)
        {
            textbox = GetTextBoxEvent();
            textbox.Text = textbox.Text.ToUpper();
        }
    }

}

將插件的項目生成的dll文件放在NotePad程序Plugin文件夾下之後，運行程序可以看到插件下多了子項，而且功能都實現了。