"You can’t build a more public entity out of a more private entity" is the Swift access control phrase in this post. Swift access controls might be confusing at times so take a look at the list of rules from Jeremy to save yourself some red compiler errors.
Massive view controllers has been a big problem for a long time, MVVM paradigm tries to solve it and Bob does a great job describing what it is. This post also shows how ReactiveCocoa can be used to communicate between view-model and view-controller.
Peter writes a case study on debugging a bug that turned out to be a regression in UIKit. Great writeup on how to debug using LLDB.
Great side-by-side comparison of Google and Apple maps design. This post goes screen by screen comparing every aspect of the two apps. Worth a read if you care about following design conventions.
Alex from Yeti writes about the design lessons they learned with over 14 updates made to the app.
If you every wondered how Yahoo weather does such smooth page transition this is the post for you. Chris shows how to animate elements inside the page with PageTransform api.
Lollipop introduced activity transitions and here is the post that explains it with an example.
Android Lollipop allows you to override theme for a View. In this post Chris describes how and why you would use it.
This is a case study from Orhan on how they updated their app from Holo to Material design.
This is a writeup on the design camp that Denis attended, they tried designing a messenger app with Material design framework. Great example of how to collaborate on design.