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Question

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.

Solution choosen:
i choose the solution from erkanyildiz with the help of a target parameter, i know its pretty low tech, but it was for me the cleanest solution. My goal was to keep the header file as small as possible. Thanks to everybody for they input, i will for sure look more into borrrdens solution with grand central dispatch when i get the time. user1055604 solution with a couple of "standard" delegates for replys is also one i like. So again thank you all for inputs.

Thanks in advance. Best regards Morten

Answer 1

Look here for an example with delegates: How to perform Callbacks in Objective-C .

It shouldn't matter that the callback is executing from within a static library .

Static libraries are a compile/link time phenomenon. As such, calls to and from within static libraries are transparent to the application at runtime.

Answer 2

Delegation pattern is a good way to do it.

You can check these pages:

http://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/CocoaFundamentals/CommunicatingWithObjects/CommunicateWithObjects.html#//apple_ref/doc/uid/TP40002974-CH7-SW18

http://en.wikipedia.org/wiki/Delegation_pattern#Objective-C_example

As another approach, you can use a target parameter in every method you have. And schedule callbacks on those targets, checking if they are responding to your callbacks using respondsToSelector

Answer 3

If you would rather not have one callback protocol declaration for each function in your static library, start with looking at what each callback would return if you did, forcefully, implement it as a callback.

From there on, find what's in common between them and bind the common elements together in a class which will serve as an interface for the responses. You may need more that one such class.

As an example, look at NSURLResponse :

---

NSURLResponse declares the programmatic interface for an object that accesses the response returned by an NSURLRequest instance.

NSURLResponse encapsulates the metadata associated with a URL load in a manner independent of protocol and URL scheme.

This class is used by NSURLConnection in its didReceiveResponse delegate method. In the worse case, you will end up with a couple of callbacks instead of a noisy header file. Happy coding. :-)

Answer 4

Try making your function calls using Grand Central Dispatch. It's quite simple, and very powerful. Here is a sample of how to make an async call with a callback:

http://pastebin.com/xDUKm6wh

This paste bin is complaining about errors, but take note of the pattern. It should work just fine.