SwiftUI Advanced

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

Quick Reference

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.