Flutter UI Design Guide

Overview

Build cross-platform Flutter apps with Material Design (Android) and Cupertino (iOS) support. This skill provides guidelines for adaptive widgets, theming, spacing, typography, and component patterns optimized for both platforms.

When to Use This Skill

Activate this skill when:

• Building Flutter UI with Material or Cupertino widgets
• Creating cross-platform app screens or layouts
• Working with Flutter development (Dart, Flutter SDK)
• Receiving requests like:
  • “Create a login screen in Flutter”
  • “Design a Flutter card layout”
  • “Build adaptive navigation in Flutter”
  • “Make this Flutter UI follow Material Design”
  • “Style this Flutter widget with Cupertino”

Do NOT activate for:

• Native iOS (SwiftUI/UIKit) only
• Native Android (Compose/XML) only
• Web development
• Backend/server code

Core Design Philosophy

Cross-Platform Principles

1. Consistency – Single codebase, pixel-perfect UI across platforms
2. Adaptive – Material (Android) and Cupertino (iOS) styles
3. Widget Composition – Reusable, composable widgets

Flexible Extensions

4. Simplicity – Clear widget tree, minimal nesting
5. Accessibility – Semantics, 48dp touch targets

Framework Approach

• Material Default: Material Design 3 widgets (Android style)
• Cupertino Option: iOS-style widgets when needed
• Adaptive Widgets: Platform auto-detection

How to Use This Skill

Step 1: Load Relevant Reference

Read references/design-principles.md - Cross-platform + adaptive design
Read references/color-system.md - Theme-based colors, dark mode
Read references/spacing-system.md - 8dp grid, EdgeInsets
Read references/typography.md - Material TextTheme, Cupertino text
Read references/component-patterns.md - Material + Cupertino widgets
Read references/anti-patterns.md - Common Flutter mistakes

Step 2: Apply Component-Specific Patterns

• Button: Material (ElevatedButton) vs Cupertino (CupertinoButton)
• Card: Material Card widget
• List: ListView.builder for performance
• TextField: Material TextField vs Cupertino CupertinoTextField
• Navigation: AppBar, BottomNavigationBar, CupertinoNavigationBar
• Dialog: AlertDialog vs CupertinoAlertDialog

Step 3: Validate Against Anti-Patterns

• ❌ Hardcoded colors (Colors.black, Colors.white)
• ❌ Fixed text sizes (no TextTheme)
• ❌ Excessive widget nesting
• ❌ setState overuse
• ❌ Column for long lists (use ListView)

Step 4: Ensure System Consistency

8dp grid:

• Use: 4.0, 8.0, 16.0, 24.0, 32.0, 48.0
• EdgeInsets.all(16.0), SizedBox(height: 16.0)

Theme colors (auto dark mode):

• Theme.of(context).colorScheme.primary
• Theme.of(context).colorScheme.onSurface
• CupertinoTheme.of(context).primaryColor

TextTheme (REQUIRED):

• Theme.of(context).textTheme.headlineMedium
• Theme.of(context).textTheme.bodyMedium

Resources

references/

• design-principles.md – Cross-platform, Material + Cupertino, widget composition
• color-system.md – ColorScheme, Theme, dark mode
• spacing-system.md – 8dp grid, EdgeInsets, SizedBox
• typography.md – Material TextTheme, Cupertino text styles
• component-patterns.md – Material + Cupertino widgets
• anti-patterns.md – Common mistakes: hardcoded colors, nesting, performance

Quick Decision Tree

Flutter UI Component Request
│
├─ Material or Cupertino? → Material default, Cupertino for iOS feel
│
├─ What spacing? → 8dp grid (spacing-system.md)
│
├─ What colors? → Theme.of(context).colorScheme (color-system.md)
│
├─ What typography? → TextTheme (typography.md)
│
└─ Validation → Check anti-patterns.md

Examples

Good Request Flow:

User: "Create a login form in Flutter"
→ Read references/component-patterns.md (TextField section)
→ Apply: TextField, Theme colors, TextTheme, 8dp spacing
→ Validate: No hardcoded colors, proper widget tree
→ Implement with Column { TextField, ElevatedButton }

Implementation Checklist:

• ✅ Spacing uses 8dp multiples
• ✅ TextTheme used (headlineMedium, bodyMedium)
• ✅ Theme colors (auto dark mode)
• ✅ Touch targets 48x48dp minimum
• ✅ Material or Cupertino widgets
• ✅ Minimal widget nesting
• ✅ ListView for long lists

Flutter Code Examples

✅ Good: Theme-Based Colors

Text(
  '제목',
  style: Theme.of(context).textTheme.headlineMedium?.copyWith(
    color: Theme.of(context).colorScheme.onSurface,
  ),
)

✅ Good: Material Button

ElevatedButton(
  onPressed: () {},
  child: Text('확인'),
)

❌ Bad: Hardcoded, No Theme

Text(
  '제목',
  style: TextStyle(fontSize: 24.0, color: Colors.black),  // ❌
)

Platform-Specific Considerations

Adaptive Widgets

Widget build(BuildContext context) {
  if (Theme.of(context).platform == TargetPlatform.iOS) {
    return CupertinoButton(child: Text('확인'), onPressed: () {});
  }
  return ElevatedButton(child: Text('확인'), onPressed: () {});
}

Dark Mode

MaterialApp(
  theme: lightTheme,
  darkTheme: darkTheme,
  themeMode: ThemeMode.system,  // Auto dark mode
)

Reference Documentation

• Flutter Design
• Material Components
• Cupertino Widgets