This repo is following Stanford University Developing iOS Objective C
https://www.youtube.com/watch?v=o3t52-ZxFtU&index=1&list=PLyjWuFyddLWNsPRqqF3cwGpQ02DhEAb0o
As an Swift iOS developer, I realize there are still lots of code bases using Objective-C. And that's why I pickup this series for learning Objective-C.