I think this should be simple, but im having a real hard time finding information about this topic. I have made a static library and have no problem getting the basics to work. But im having a hard time figuring out how to make a call back from the static library to the main APP.

I would like my static library to only use one header as front, this header should contain functions like:
requestImage:(NSString *)path;
requestLikstOfSomething:(NSSting *)guid;
and so on..

These functions should do the necessary work and start a async NSURLConnection, and call back to the main application when the call have finished. How do you guys do this, what are the best ways to callback from a static library when a async method is finished? should i do this with delegates (is this possible), notifications, key/value observers. I really want to know how you guys have solved this, and what you regard as the best practices.

Im going to have 20-25 different calls so i want the static library header file to be as simple as possible preferable only with a list of the 20-25 functions.

UPDATE:
My question is not how to use delegate pattern, but witch way is the best to do callbacks from static librarys. I would like to use delegates but i dont want to have 20-25 protocol declarations in the public header file. I would prefer to have only one function for each request.

Thanks in advance. Best regards Morten