interface Ipeople
 {
  void say();
 }

 public class man : Ipeople
 {
  public void say()
  {
   MessageBox.Show("man");
  }
 }

 public class woman : Ipeople
 {
  public void say()
  {
   MessageBox.Show("woman");
  }
 }

 private static void NewMethod(string tpye)
  {
   Ipeople ib = null;
   var types = AppDomain.CurrentDomain.GetAssemblies()
      .SelectMany(a => a.GetTypes().Where(t => t.GetInterfaces().Contains(typeof(Ipeople))))
      .ToArray();
   foreach (var v in types)
   {
    var attribute = v.GetCustomAttributes(typeof(NameAttribute), false).FirstOrDefault();
    if (attribute != null && ((NameAttribute)attribute).Name == tpye)
    {
     ib = (Ipeople)v.Assembly.CreateInstance(v.FullName);
     break;
    }
   }
   if (ib != null) ib.say();
  }