moving a function to a background thread in objective c

Question

I have a function that returns a string that takes 15 seconds to compute on an iPhone.

I want to be able to run the function on the background thread so that the main thread can be used for the user interface.

I've heard GCD is a new technology that is good for this, can someone provide some example code in regards to how this would work?

That is to run a generic function on the background thread and return the result to a UI text field.

EDIT:

Thanks Alladinian it works a treat.

However, when I use GCD my function takes 1 second longer to execute on the iphone simulator (I'd guess this'd be about 5 seconds on an iphone (ill have to test it later today to be sure))

Is there any reason why this is? Perhaps the background thread is slower or something?

Answer 1

Well that's pretty easy actually with GCD. A typical workflow would be something like this:

dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0ul); dispatch_async(queue, ^{     // Perform async operation     // Call your method/function here     // Example:     NSString *result = [anObject calculateSomething];     dispatch_async(dispatch_get_main_queue(), ^{         // Update UI         // Example:         self.myLabel.text = result;     }); }); 

For more on GCD you can take a look into Apple's documentation here

Answer 2

Also to add, sometimes you don't need to use GCD, this one is very simple to use :

[self performSelectorInBackground:@selector(someMethod:) withObject:nil];