Factory method pattern implementation in .net framework

Posted Jan 3, 2019

Factory method pattern also called as Virtual Constructor (less known), defines an interface for creating objects, but defer the instantiation to sub-classes.

Read more about the pattern: Wikipedia, dofactory, Sourcemaking, oodesign, etc.

I can safely state, that: A well designed library cannot exist without implementing factory method pattern.

We can see .net framework implementing this pattern extensively, few examples:

System.Activator.CreateInstance(Type type)
System.Net.WebRequest.Create(string requestUriString) based on the url scheme, if url starts with http://, a System.Net.HttpWebRequest instance will be returned. For ftp:// a System.Net.FtpWebRequest.
System.Convert.ToInt32, System.Convert.ToBoolean, etc.
System.Web.Mvc.DefaultControllerFactory.CreateController(RequestContext requestContext, string controllerName) based on controllerName parameter, this method returns instance specified.