Where To Go From Here?
In one single app, you’ve created a clean, object-oriented application using basic objects, inheritance, MVC design, polymorphism, as well as singleton and factory methods. You can review the source code of the finished project here.
For more information on singletons, you can read Mike Ash’s definitive, incredibly detailed post on the Care and Feeding of Singletons.
If you’d like more information about Object-Oriented patterns, Eli Ganem wrote a great tutorial called iOS Design Patterns that reviews a bit of what you’ve learned here, then introduces you to several more advanced design patterns that you can use to construct even more elegant code.
If you’ve got questions, please ask away in the comments below!
