Objective-C Programming: The Big Nerd Ranch Guide

Challenge: using a block with NSNotificationCenter

In Chapter 27, you used NSNotificationCenter’s addObserver:selector:name:object: method to register to receive callbacks via your zoneChange: method. Update that exercise to use the addObserverForName:object:queue:usingBlock: method instead.

This method takes a block as an argument and then executes the block instead of calling back to your object when the specified notification is posted. This means that your zoneChange: method will never be called. The code that was inside this method will instead be in the block.

The passed-in block should take a single argument (an NSNotification *) and return nothing, just as the zoneChange: method does.

Pass nil as the argument for queue:; this ...