1     /// <summary>命令接口</summary>
 2     public interface ICommand
 3     {
 4         /// <summary>命令名称</summary>
 5         string Name { get; }
 6 
 7         /// <summary>执行命令</summary>
 8         /// <param name="cmd">命令参数</param>
 9         /// <returns>返回的结果</returns>
10         string Excute( string cmd );
11 
12         /// <summary>对命令的使用作相应的说明</summary>
13         string Describe { get; }
14     }
15     /// <summary>获得插件的窗体</summary>
16     public interface IForm
17     {
18         /// <summary>窗体名</summary>
19         string Text { get; }
20 
21         /// <summary>窗体对象</summary>
22         Form GetForm { get; }
23     }

public partial class frmSuperCalculator : Form, IForm
{
        string IForm.Text {
            get { return "计算器"; }
        }

        frmSuperCalculator frm;
        Form IForm.GetForm {
            get {
                if (frm == null || frm.IsDisposed) {
                    frm = new frmSuperCalculator();
                }
                return frm;
            }
        }
        ...  
}

public class Calculator : MathAssistLibrary.ICommand
{
        string MathAssistLibrary.ICommand.Describe {
            get { return "cal命令可以进行相关的数学运算。比如cal 1+max(2,3)*2"; }
        }
        string MathAssistLibrary.ICommand.Name {
            get { return "cal"; }
        }
        string MathAssistLibrary.ICommand.Excute(string cmd) {
            try {
                Expression exp = new Expression();
                exp.Format = cmd;
                return exp.Calculator().ToString();
            } catch (ExpressionException e) {
                return string.Format("表达式出错。出错类型:{0},出错位置{1}", e.Message, e.Index);
            }
        }
}

 1         List<string> FindDllFile(string foldername) {
 2             DirectoryInfo dir = new DirectoryInfo(foldername);
 3             FileInfo[] files = dir.GetFiles();
 4             List<string> result = new List<string>();
 5 
 6             foreach (FileInfo fi in files) {
 7                 if (fi.Name.ToUpper().EndsWith(".DLL"))
 8                     result.Add(fi.FullName);
 9             }
10             return result;
11         }

        private List<object> LoadOne(string filename, Type type) {
            List<object> result = new List<object>();

            try {
                Assembly ass = Assembly.LoadFrom(filename);
                Module[] mods = ass.GetModules();

                foreach (Module mod in mods) {
                    Type[] typs = mod.GetTypes();

                    foreach (Type typ in typs) {
                        if (type.IsAssignableFrom(typ)) {
                            result.Add(ass.CreateInstance(typ.FullName));
                        }
                    }
                }
            } catch (BadImageFormatException) {

            }
            return result;
        } // end func

List<object> cmd = LoadOne(filename, typeof(ICommand));
List<object> frm = LoadOne(filename, typeof(IForm));