Borrowing from Kotlin/Android to Architect Scalable iOS Apps in SwiftUI

As an iOS developer, creating scalable architecture for a complex app can be a daunting task. Traditional approaches often rely on trial and error, relying on personal experience or Apple's sample code to guide the development process. However, with the rise of modern Android development, it's time to rethink our approach.

In this article, we'll explore how to build scalable iOS apps using architecture patterns inspired by Kotlin and Android development. We'll delve into state management, action-based updates, screen separation, layered data flow, and reactive repositories – all essential components of a robust iOS app architecture.

Solving the State Problem: Explicit State

In Kotlin, the state problem is solved at the type level. The state is defined by a single source of truth, making it mutually exclusive and enforced by the compiler. This approach prevents contradictory states and provides a clear contract for mutations.

However, in traditional iOS development with SwiftUI, managing state can become convoluted. Views often contain complex logic, leading to tight coupling between views and their view models. This makes it challenging to test, debug, and maintain the codebase as it grows.

Single Entry Point for Mutations

Kotlin's answer to the mutation problem is a single entry point: every mutation flows through `onAction()`. This ensures that all mutations are explicitly defined, making it easy for new engineers to understand the ViewModel's capabilities.

This approach also forces developers to think about their ViewModel's responsibilities. When adding a new action, it's added to the sealed class first, making it clear and concise.

Screen Separation: A Missing Layer

Traditional iOS development often blurs the lines between screen logic and view model logic. This tight coupling makes it challenging to reuse code, test, or debug individual components.

In modern Android development, a standard pattern separates screens from content. The screen is a wrapper that owns the ViewModel, while the content is a composable that just renders the UI.

Layered Data Flow: Unidirectional Data Flow

Android's unidirectional data flow (Event -> View -> ViewModel -> Repository -> API) is an essential concept in modern app development. This approach ensures that each layer only knows about the layer below it, making it easier to test, mock, and replace individual components.

R reactive Repositories: A Single Source of Truth

The reactive repository pattern provides a single source of truth for data. Every screen observes this single copy of the data, ensuring that updates propagate automatically across the app.

This approach eliminates the need for callbacks, notifications, or manual refreshing, making it easier to test and maintain the codebase.

A Scalable iOS App Architecture

By adopting patterns proven in the Android ecosystem, including explicit state management, action-based updates, screen separation, layered data flow, and reactive repositories, we can build scalable iOS apps that are easy to maintain and extend.

This approach ensures cleaner code, reduces the risk of stale data across dozens of screens, and makes it easier for new engineers to join the team without reinventing the wheel.

By embracing this architecture, we can create robust, maintainable, and scalable iOS apps that meet the demands of modern app development.

Join us in exploring the world of modern iOS app development and discover how to build scalable, maintainable, and efficient apps using patterns from the Android ecosystem.

This content is part of our Mobile topic series. Stay tuned for more articles on mobile app development, architecture, and best practices.