Question

I am currently thinking about the data-model for my iOS App. The app does only receive Information from a server and therefore, the “model” itself generally does all the web-requests, …
However, these network requests have to be performed in the background – I mean another task, not the iOS background state – and after the request has finished, the information in the Application has to be updated.

Would it make more sense to write a delegate to inform the controller or could I also use NSNotificationCenter? I think an NSNotification-based solution could make the model more universal, e.g. in a desktop application.
And maybe, I should add: the model (since it saves some session Information) is a singleton, so a regular delegate based method would not work…

Answer 1

I don’t think that it would be a good idea to use a separate thread to handle the communication. Apart from being complex, it is not necessary since NSURLConnection/NSURLRequest do allow you to handle communication asynchronously, i.e., without blocking.

In detail, you can create an NSURLRequest executing:

NSURLRequest* yourReq = [NSURLRequest requestWithURL:yourURL];

then create an NSURLConnection with:

NSURLConnection* yourConnection = [NSURLConnection connectionWithRequest:yourReq delegate:yourDelegate];

and start it with:

[yourConnection start];

When the data is ready, one of the methods for your delegate (connectionDidFinishLoading:, or connection:didFailWithError:) will be called so that you can update your UI.

All this without blocking.

An even better alternative to using NSURLConnection/NSURLRequest, is using ASIHTTPRequest, which seems to be more resilient as to memory management and also offers a great caching mechanism.

EDIT: if your concern is that being your model a singleton, you cannot have a delegate, let me suggest that you look further into the matter.

Your model may be a singleton and the delegate to your request may have nothing to do with the model, apart from knowing how to access it (which is pretty trivial being the model a singleton).

This is possible by several mechanisms with NSURLConnection, but if you use ASIHTTPRequest, it will become really easy, because each ASIHTTRequest can have its own delegate.