SwiftUI Advanced

Advanced SwiftUI patterns for gesture composition, adaptive layouts, architecture decisions, and performance optimization.

Reference Loading Guide

ALWAYS load reference files if there is even a small chance the content may be required. It’s better to have the context than to miss a pattern or make a mistake.

Core Workflow

1. Identify pattern category from user’s question
2. Load relevant reference for detailed patterns and code examples
3. Apply pattern following the decision trees and anti-patterns
4. Verify using provided checklists or profiling guidance

Decision Trees

Gesture Composition

• Both gestures at same time? -> .simultaneously
• One must complete before next? -> .sequenced
• Only one should win? -> .exclusively

Layout Adaptation

• Pick best-fitting variant? -> ViewThatFits
• Animated H/V switch? -> AnyLayout
• Need actual dimensions? -> onGeometryChange

Architecture Selection

• Small app, Apple patterns? -> @Observable + State-as-Bridge
• Complex presentation logic? -> MVVM with @Observable
• Rigorous testability needed? -> TCA

Common Mistakes

1. Gesture composition order matters — .simultaneously and .sequenced have different trigger timing. Swapping them silently changes behavior. Understand gesture semantics before using.

2. ViewThatFits over-used — ViewThatFits remeasures on every view change. For animated H/V switches, use AnyLayout instead. Use ViewThatFits only for static variant selection.

3. onGeometryChange triggering unnecessary updates — Reading geometry changes geometry, which triggers updates, which changes geometry… circular. Use .onGeometryChange only with proper state management to avoid loops.

4. Architecture mismatch mid-project — Starting with @Observable + State-as-Bridge then realizing you need TCA is expensive. Choose architecture upfront based on complexity (small app = @Observable, complex = TCA).

5. Ignoring view body optimization — Computing expensive calculations in view body repeatedly kills performance. Move calculations to properties or models. Profile with Instruments 26 before optimizing prematurely.