Quick question –– we could troubleshoot this some more and I’m sure a straightforward reason will shake out once we get the logging turned on (I’m almost certain at this point that it is because you’re referencing the ivars you created with the underscores in front of them –– an ivar is an instance variable of a class and that convention with the underscore is intended to make it clear when an instance variable is being referenced rather than a property, but the tutorial code is designed to only ever reference by class property), but why don’t you just exactly copy and paste the tutorial code since it is known to work?
The tutorial is designed to avoid any possible memory management or referencing mistakes that can happen with objects that perform many asynchronous operations with callbacks over their lifetime, and the changes you’ve made to it aren’t that minor since they change the way that those objects are addressed in a way that works around those failsafes.
Can you start by doing a complete copy and paste so we can have a clean slate, and then once that is working, go ahead and ask me the questions about changes you’d like to make that led to making those alterations?