Introduction

Congratulations on making it to Lesson 3! In Lessons 1 and 2, you learned the fundamentals of Swift SDK for Android development:

• Lesson 1: Swift-Java interop basics, building simple computations that bridge Swift and Kotlin.
• Lesson 2: Camera integration and image processing with SwiftUI-like patterns, capturing photos and applying filters.

These lessons taught you how to write Swift code that runs on Android and how to connect it to Kotlin UI. But there’s a critical limitation: everything you’ve built so far disappears when the app closes.

Create a task list? Gone after restart. Capture a photo? Lost. Apply a filter? You’ll never see it again.

This isn’t just inconvenient, it makes your apps essentially unusable in the real world. Professional mobile apps must persist data across launches, app updates, and even device reboots. Without persistence, users lose trust and abandon your app.

In this lesson, you’ll learn how to implement production-quality data persistence using file-based storage, giving your apps the reliability users expect.

What You’ll Learn

By the end of this lesson, you’ll know how to:

• Implement file-based persistence using Swift’s Codable protocol for JSON serialization.
• Handle binary file management for photos separate from JSON data.
• Build complete CRUD operations (Create, Read, Update, Delete) across the Swift-Kotlin boundary.
• Use Result types for explicit, type-safe error handling in Swift.
• Implement atomic file writes to prevent data corruption.
• Handle cross-platform file paths (iOS vs Android differences).
• Create JNI exports to bridge Swift methods to Kotlin.
• Synchronize UI with StateFlow for reactive updates.
• Implement two-layer validation (Kotlin for UX, Swift for safety).
• Build edit functionality with pre-populated forms in Compose.
• Test persistence, validation, and edge cases comprehensively.