creating methods with Completion Handler

You can use a block passed into the initiating call. Store the block and call it when the async call finishes.

Depending on how you are running the async code you might need to marshal the block call back to the main thread with a dispatch async on the main queue if your callback is updating the UI.

 

Consider the following

Code:

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
	
	// doing serious heavy work...
	myInt = 1000 * 1000;
	
	dispatch_async(dispatch_get_main_queue(), ^{
		
		[self myMethodToUpdateUIAfterHeavyWork];
	});
});

If you do your heavy work inside a block like this you can then call your next method once the work has completed. If your next method doesn't have to run on the main thread you can just call it after the calculation of myInt is done.