iOS - app interface freezes up on startup during network calls

Question

The app I am working on fetches a bunch of different newsfeeds when it first starts up and updates any expired ones. While this is happening the interface often freezes up and you can't click anything. The actual network calls are being done on a separate thread, but the database operations are being done on the main thread. Would this cause the interface to freeze?

I have been told that I need to make it to where only two feeds to update are inserted into the network operation queue at a time so that it won't try all of them at once, but it's already set up to only do so many network calls at once. I don't understand how having less things in a queue at a time would cause it to go faster if they're just going to be put in there sequentially anyways. Please correct me if I am wrong, I'm still pretty new to this.

Any kind of help regarding what could cause the UI to freeze up during startup like this would be much appreciated!

Answer 1

It is always a good idea to move time consuming operation away from the main thread.

Fortunately it is pretty simple to do on iOS. If the time-consuming task is fairly simple you could consider using performSelectorInBackground

eg:

 [self performSelectorInBackground:@selector(myFunction:)
    withObject:myParam];

It is however important to remberber, that you must not access the GUI from the background thread. To get objects back to the main thread use performSelectorOnMainThread

eg:

 [self performSelectorOnMainThread:@selector(myFunction:) myParamwaitUntilDone:YES];

Try applying this strategy to your database calls. Depending on your scenario you might want to wrap it up in a NSOperation or use a Thread when the cause of the freeze is found.