Architecture & Design Patterns for iOS
building maintainable and scalable applications
About this book
Over the years as an iOS developer, I’ve had the opportunity to work on a variety of projects, each with its own unique challenges and lessons. One thing that's become clear quickly is how crucial good architecture and design patterns are to building apps that are maintainable, scalable, testable, and enjoyable to work on.
But understanding architecture is rarely straightforward. Each pattern comes with countless interpretations, trade-offs, and strong opinions. Trying to make sense of it all, especially when every project has its own constraints, can feel overwhelming. There's no single "perfect" architecture, no universal blueprint that fits every app.
My goal with this book isn't to prescribe a one-size-fits-all architecture, but to offer a set of tools and perspectives to help make informed decisions. The approaches explored here are shaped by real-world experience and aim to be both practical and adaptable. Whether starting a new app or evolving an existing codebase, I hope this book becomes a resource to return to.
Structure of this book
Chapter 1: The importance of architecture
Every software project, whether small or large, is shaped by architectural decisions, some intentional, others implicit. In this chapter, we’ll take a step back to understand what architecture really means in the context of iOS development. We'll explore the scope of architectural thinking, why it matters for long-term maintainability, and how to strike the right balance between overengineering and underplanning. We'll also look at how iOS architecture has evolved over the years.
Chapter 2: Designing with protocols in Swift
After looking at why architecture matters, we now move into what it looks like in practice. One useful tool Swift gives us are protocols. From building testable code with protocol-based mocking to designing flexible APIs, protocol-oriented thinking is foundational to many modern Swift architectures. In this chapter, we'll explore how protocols are used to define boundaries, structure modular Swift codebases and enable testing.
Chapter 3: Dependency injection in Swift
After exploring how protocols define boundaries between components, we'll now look at how to make those boundaries work in practice. To do that, we need a way to provide the right dependencies to the right places at the right time. And that's where dependency injection comes in. In this chapter, we'll explore what dependency injection is and learn about common DI techniques in Swift.
Chapter 4: Navigation and routing in SwiftUI
After exploring how to manage dependencies and decouple application logic, we now turn to another foundational aspect of app architecture: navigation. Navigation is a fundamental aspect of any iOS application, defining how users move between screens and interact with different parts of the app. As the app scales, managing navigation can become challenging unless implemented in a way that allows flexibility and extensibility. Handling deep linking, managing navigation between different domains or modules, and keeping navigation logic decoupled from the UI layer are just a few of the challenges that arise. In this chapter, we will explore how SwiftUI handles navigation and how we can build a routing system that promotes separation of concerns and maintainability.
Chapter 5: Applying key design patterns in Swift
The techniques we discovered so far help us build scalable systems and at the same time, they introduce recurring challenges around how we create, compose, and adapt objects. Design patterns offer time-tested solutions to these challenges. They provide reusable blueprints for things like object creation, state management, and communication between layers. Additionally, design patterns provide a shared language that makes it easier to communicate ideas and collaborate effectively with other developers. In this chapter, we'll look at a selection of foundational design patterns and apply them to practical use cases.
Chapter 6: From observers to reactive streams
Building on core design patterns, we will now explore how reactive programming offers a declarative approach to handling asynchronous data and events. In this chapter, we'll learn how reactive programming builds on the familiar observer pattern, how Combine lets us create and transform complex streams of values, how Swift concurrency offers reactive patterns, and how these concepts integrate into app architecture.
Chapter 7: Structuring SwiftUI apps
When building a SwiftUI app, deciding how to structure the code is one of the most important architectural choices. There are multiple ways to organize SwiftUI applications, ranging from patterns like MVVM to approaches like The Composable Architecture. Some approaches focus on separating concerns to keep the UI, business logic, and data handling distinct, while others emphasize unidirectional data flow or reactive state management. This chapter explores different strategies for structuring SwiftUI apps, helping you get an overview and choose a suitable approach.
Chapter 8: Modularization with Swift Package Manager
As apps grow in size and complexity, modularization can help maintain clarity, control build times, and improve team collaboration. It's a core architectural decision that sets the foundation for how a project evolves over time. Swift Package Manager is Apple's native tool for managing dependencies in Swift projects. In addition to integrating third-party libraries, it can also be used to organize internal code into separate packages. This makes it possible to structure larger projects into modular components with clear boundaries. In this chapter, we'll explore what strategies can help structure a codebase as it grows.