Building a SwiftUI Line-Art System with Claude Code: One Good Thing Case Study

Developer Evening-Strike-2021 built an iOS app called One Good Thing (free on App Store) with Claude Code as the primary coding partner. The app presents one thoughtful card per day with a simple interaction: Carry it or Let Go, then close — no feed, no endless scroll. The most notable technical choice: every illustration is drawn in code using SwiftUI Canvas paths, no image files.

Claude Code Workflow for Vectors

The developer describes a specific, non-prompt-chaining approach:

• Describe the feeling of the screen in plain language
• Ask Claude for a rough Canvas implementation
• Run it in the app and manually tune coordinates until it feels less like an icon than a small expressive mark
• Ask Claude to simplify or harden the code once direction feels right

This loop — generate, inspect, adjust, reduce — produced hand-drawn style line art (hands, birds, windows, threads, dots, curves) entirely via Bezier curves in SwiftUI Canvas.

Claude's Specific Contributions

• Turning vague visual direction into first-pass SwiftUI Canvas paths
• Refactoring repeated drawing logic for consistency across illustrations
• Catching SwiftUI edge cases around view state, animations, and previews
• Helping reason through Firebase, StoreKit, Cloud Functions, App Check, and Firestore rules without losing product focus

Broader Stack

The app uses Claude-assisted code across the entire stack: SwiftUI for iOS, Firebase Cloud Functions, Firestore security rules, a Next.js landing page, and AI reflection features for subscribers. The line-art system is the most visible outcome, but the collaboration pattern applied throughout.

Key Takeaway

The biggest lesson from the build: Claude is much better when treated like a patient pair programmer, not a vending machine. It gets a usable first draft on screen quickly, but taste and direction must come from the developer.