Exploring Rendering in SwiftUI

Learn when SwiftUI re-render subviews

Photo by Viktor Forgacs on Unsplash

One of the amazing aspects of the Software engineering profession is that you never stop learning. You are exposed every day to different technologies: learning their basic concepts is one of the things that I personally like the most.

One of the most important skills to learn new technologies is the ability to recognize patterns and similarities. This allows you to reason about a new technology even if you don’t use it every day.

A week ago, a colleague of mine sent me this article on React rendering. I don’t use React every day, but I am familiar with its basic concepts and I couldn’t notice how similar SwiftUI it is. While reading the article, I was surprised to see that React re-renders when the state of a Component changes and not when its props do.

So, my curiosity tingled: what does SwiftUI do? When does it re-render its components? I created a small project to try and understand that and today I want to share my process and my findings.

Recreating the App

The first step I took was to reproduce the same situation of the one presented in the article. I created a new SwiftUI project with the same initial components:

• The BigCountNumber