Maintaining, Modernizing, and Migrating Legacy Code to Swift

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Plenty of successful iOS and macOS apps still run on Objective-C, and someone has to keep them working.

Maybe you are a Swift developer who has just inherited a codebase full of square brackets. Maybe you are maintaining a long-lived macOS utility. Or maybe you wrote Objective-C years ago and now need to modernize an aging project and plan its move to Swift. This book is written for all three situations.

You learn the language properly, then use it on a realistic legacy app. Fieldbook is a fictional ten-year-old field-research app with a giant data-manager singleton, massive view controllers, hand-written JSON parsing and very few tests. Over 28 chapters you read it, test it, debug it, modernize it, and migrate key features to Swift and SwiftUI, keeping the app shippable at every step.

WHAT'S INSIDE
➔ 496 pages · 28 chapters in 6 parts + 4 appendices
➔ Objective-C from the ground up: messages, classes, headers, properties, and ARC
➔ Foundation, protocols, categories, blocks, Grand Central Dispatch, and error handling
➔ The Objective-C runtime: dynamic dispatch, introspection, and method swizzling
➔ Delegation, target-action, notifications, KVC, and KVO
➔ UIKit and AppKit apps: view controllers, Auto Layout, table views, networking, and Core Data
➔ Reading, testing (XCTest), debugging (Instruments), and modernizing legacy code
➔ Nullability, lightweight generics, and NS_SWIFT_NAME for great Swift interop
➔ Planning and running an incremental migration to Swift and SwiftUI
➔ Hands-on case studies, plus a cheat sheet, a translation reference, and a migration checklist

Table Of Contents

PART I — OBJECTIVE-C FOUNDATIONS

• Ch 1 · Why Objective-C Still Matters: Legacy Apps, Apple Frameworks, and Your Career
• Ch 2 · The Toolchain: Xcode, Clang, Projects, and Your First Objective-C Program
• Ch 3 · Syntax Essentials: C Roots, Messages, Classes, Methods, and Headers
• Ch 4 · Objects, Properties, and Memory Management with ARC
• Ch 5 · The Foundation Framework: Strings, Collections, Numbers, Dates, and Literals

PART II — THE LANGUAGE IN DEPTH

• Ch 6 · Protocols, Categories, and Class Extensions
• Ch 7 · Blocks and Grand Central Dispatch
• Ch 8 · Error Handling: NSError, Exceptions, and Assertions
• Ch 9 · The Objective-C Runtime: Messaging, Introspection, Dynamic Dispatch, and Method Swizzling
• Ch 10 · Communication Patterns: Delegation, Target-Action, Notifications, KVC, and KVO

PART III — BUILDING APPS WITH UIKIT AND APPKIT

• Ch 11 · UIKit Fundamentals: App and Scene Lifecycle, View Controllers, and the Responder Chain
• Ch 12 · Views, Auto Layout, Table Views, and Collection Views
• Ch 13 · Navigation, Storyboards, XIBs, and Building UI in Code (with AppKit notes)
• Ch 14 · Networking with NSURLSession and JSON
• Ch 15 · Persistence: NSUserDefaults, Files, NSSecureCoding, and Core Data

PART IV — MAINTAINING LEGACY CODE

• Ch 16 · Reading and Understanding a Legacy Codebase
• Ch 17 · Modern Objective-C: Nullability, Lightweight Generics, Literals, and Modern Syntax
• Ch 18 · Testing Legacy Objective-C with XCTest
• Ch 19 · Debugging and Instruments: Leaks, Retain Cycles, Zombies, and Crashes
• Ch 20 · Modernizing the Project: Build Settings, Warnings, Dependencies, and Deprecated APIs

PART V — INTEROPERABILITY AND MIGRATION TO SWIFT

• Ch 21 · Using Objective-C from Swift: Bridging Headers, Nullability, and NS_SWIFT_NAME
• Ch 22 · Using Swift from Objective-C: @objc, the Generated Header, and Limitations
• Ch 23 · Planning an Incremental Migration: Strategy, Order, and Risk Management
• Ch 24 · Migrating Models, Networking, and Persistence to Swift
• Ch 25 · Migrating UI: From UIKit View Controllers to SwiftUI with UIHostingController

PART VI — CASE STUDIES

• Ch 26 · Case Study: Modernizing Fieldbook Without a Rewrite
• Ch 27 · Case Study: Migrating the Observations Feature End to End
• Ch 28 · Living with a Mixed Codebase: Long-Term Maintenance and Team Practices

APPENDICES

• App A · Objective-C Cheat Sheet
• App B · Objective-C to Swift Translation Reference
• App C · Legacy Modernization and Migration Checklist
• App D · Glossary

WHO IT IS FOR
This book is for:

• Swift developers who maintain or inherit Objective-C code.
• iOS and macOS developers returning to Objective-C after years away.
• Teams planning a gradual migration to Swift.
• Developers who want to understand the Objective-C foundations that Apple's frameworks were built on.

Basic programming knowledge is assumed. Familiarity with Swift helps but is not required.

FORMAT
PDF (A4), 496 pages, English, clickable table of contents and PDF bookmarks. 1st Edition, 2026. Published by thenexbooks. Not affiliated with or endorsed by Apple Inc.

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