Use System.Activator.CreateInstance

/// <summary>
  /// 得到给定一个IMessageDetail的实现类的实例的工厂
  /// </summary>
  /// <param name="className">IMessageDetail的实现类的类名，此类名包括完整的域名空间</param>
  /// <returns>IMessageDetail的一个实例</returns>
  public static IMessageDetail CreateMessageDetailHandler(string className)
  {
   try
   {
    string assemblyName = MessageConfig.GetAssemblyLocation() + "/" + GetAssemblyName(className);

    // load assembly
    Assembly targetAssembly = null;

    if(assemblyName != string.Empty)
    {
     targetAssembly = Assembly.LoadFrom(assemblyName + ".dll");
    }

    // create AMessageMgr insatance
    if(className == null || className == string.Empty)
    {
     return null;
    }
    else
    {
     // get class type
     System.Type type;

     try
     {
      if(targetAssembly == null)
      {
       type = System.Type.GetType(className);
      }
      else
      {
       type = targetAssembly.GetType(className);
      }
     }
     catch
     {
      type = null;
     }

     // get AMessageMgr instance
     if(type == null)
     {
      return null;
     }
     else
     {
      object messageHandler = System.Activator.CreateInstance(type);
      return (IMessageDetail)messageHandler;
     }
    }
   }
   catch
   {
    return null;
   }
  }