Developing declarative and functional iOS apps with SwiftUI and Combine

Native app development was imperative and object oriented, having all side effects those paradigms usually bring with them. With two new native swift frameworks, I’ve developed several apps with completely declarative UI code and functional event handling and logic, one of them in production in the finance sector. I want to share my experiences and give an overview of those frameworks, with their advantages, downsides and common pitfalls.

Last summer there was a big hype among iOS developers for a brief moment: Apple released two new, completely different frameworks for UI and event handling. After a first hype, few have been brave enough to directly adapt those frameworks in production code with most developers waiting for others to test how they perform in production. Luckily, I had the opportunity to use both frameworks in a real product in the finance sector, aiming at real customers and experiencing the state of production-readiness of these frameworks as well as how good they scale when your app gets bigger.

SwiftUI is a new native UI framework for Apple operating systems. It has a declarative syntax, reducing the amount of code necessary for UI programming and removing the necessity to use imperative code in applications.

Combine is an event handling framework released simultaneously which is heavily inspired by ReactiveX. It is asynchronous and uses a functional syntax and greatly improves handling asynchronous events like user input or network requests.

In my tutorial, I will show how it is possible with these frameworks to create iOS apps with (almost) no imperative code, using a purely declarative UI and async, functional event handling. I also want to show a few examples of typical mistakes people make when they use these frameworks and in which parts of the app it might still be safer to resort to the conventional frameworks used there.

Setup

If you want to try to follow coding yourself, you will unfortunately only be fully able to do that on MacOS, where you just need to install Xcode (from the App Store).

If you want to try around a bit on Linux, follow the steps on

https://github.com/SwiftWebUI/SwiftWebUI

and have a code editor with Swift syntax highlighting (I would recommend VSCode, but Atom, Vim, Emacs, every other code editor works.) If you are using Windows, you’ll need to use Docker or WSL, and then follow the Linux steps.

The tutorial code is here:

https://github.com/Hustenbonbon/SwiftUICombineTutorial/

Max Tharr

Max is a fullstack developer at Mayflower. He develops mobile and web apps, with a focus on UX and modern programming paradigms like declarative, functional and reactive programming. He comes from an Augmented Reality and Games Engineering background and has a heart for Open Source.