In the previous post, Advanced iOS Concurrency: Operations, we walked through the Operation concepts on iOS and made a demo application that fetches some posts of mine. After downloading the cover images, they will be applied to a simple filter, then be displayed in a table view. The application, however, has not been completed yet. There’s something that went wrong with our app making the app did not show downloaded images properly. In this tutorial, we will continue where we left off.
Get ready!

There are two techniques to deal with Concurrency in iOS: GCD - Grand Central Dispatch and Operations. Most of the time, GCD provides most of the concurrency capabilities you need. Yet, sometimes you’ll want some extra advanced customizations. It’s time to use Operations. This tutorial will introduce Operations in Swift, also explain when and why we use Operation instead of GCD.
Let’s switch the gears!

There is a big gap between knowing the path and walking through the path.

Some applications can survive without any data storage. Most other useful applications, however, save some state such as user configurations, user profile, goals, etc. on iOS, Apple provides Core Data as a framework to persist your valuable data. One thing to keep in mind that although CoreData can store data in a relational database it’s actually not a database engine.
In this tutorial, I will share with you a bad experience I faced when I work with Core Data. Hopefully, after reading my sharing, you will avoid facing the same problem in your projects.
Let’s get started.

As you might know, the word “Thread safe” is referred to a computer science concept in the context of multi-thread programs. A code is called “Thread safe” if any shared data is accessed by only one thread at any given time. Notice these shared data are called critical sections in an operating system.
The point is Swift collection types like Array and Dictionary are not thread-safe when declared mutable (With var keyword).
In this post, we will discuss some techniques to make our code thread safe in iOS.