Obtain all content types on the site.

Spcontenttypeid  ID  =  New  Spcontenttypeid  (  Basecontenttypeid  );  
  Ilist  <  Spcontenttype  >  Contenttypes  =  Web  .  Contenttypes  .  Cast  < Spcontenttype  > ().  Where  (  C  =>  C  .  ID  .  Ischildof  (  ID  )).  Tolist  ();



 

 Using  (  Spsite  Site  =  New Spsite  (  Spcontext  .  Current  .  Site  .  URL  ))  
  {  
  Using  (  Spweb  Web  =  Site  .  Openweb  ()) 
  {  
  Spcontenttypecollection  Allcontenttypes  =  Web  .  Contenttypes  ;  
  Spcontenttypecollection  Doccontenttypes  =  Null  ;  
  Foreach (  Spcontenttype  Objcontenttype  In  Allcontenttypes  )  
  {  
  If  (  Objcontenttype  .  Parent  .  Name  =  "Document"  ) 
  {  
Doccontenttypes  .  Add  (  Objcontenttype  );  
  }  
  }  
 // Doccontenttypes contains all content types derived from content type "document". You can implement additional checks and add this into a drop down list.  
  }  
  } 

 
You can use the name to retrieve:
 

 
SpcontenttypeSpct=Web.Availablecontenttypes["Contenttypename"];