flutter-ui-design（Flutter UI 设计）

Flutter UI Design Guidelines

Purpose

This skill provides guidelines to make Flutter app UIs stand out from "typical defaults" and achieve professional, impressive designs.

Typography

Patterns to Avoid

• Using only default Roboto
• Monotonous font weights (Regular/Bold only)
• Uniform text sizes

Recommended Approach

// Use modern fonts with Google Fonts
import 'package:google_fonts/google_fonts.dart';

// For titles: Distinctive display fonts
GoogleFonts.poppins(fontWeight: FontWeight.w700)
GoogleFonts.inter(fontWeight: FontWeight.w800)
GoogleFonts.plusJakartaSans()

// For body: Readable sans-serif
GoogleFonts.inter()
GoogleFonts.dmSans()

// Size hierarchy with contrast in mind
headlineLarge: 32sp, weight: 800
headlineMedium: 24sp, weight: 700
titleLarge: 20sp, weight: 600
bodyLarge: 16sp, weight: 400
labelSmall: 12sp, weight: 500

Font Weight Usage

• Extreme contrast: Combine w300 and w800
• Bold for headings (w600-w800), regular for body (w400)

Color & Theme

Patterns to Avoid

• Material Design default blue/purple
• Subtle, uniform color palettes
• Gray-only safe UIs

Recommended Approach

// Dark theme: Deep background + vivid accents
ColorScheme.dark(
  surface: Color(0xFF0F0F14),        // Deep dark gray
  surfaceContainerHighest: Color(0xFF1A1A23),
  primary: Color(0xFF6366F1),         // Vivid indigo
  secondary: Color(0xFF22D3EE),       // Cyan accent
  tertiary: Color(0xFFF472B6),        // Pink accent
)

// Light theme: Clean white + vivid accents
ColorScheme.light(
  surface: Color(0xFFFAFAFC),
  surfaceContainerHighest: Color(0xFFF1F5F9),
  primary: Color(0xFF4F46E5),         // Indigo
  secondary: Color(0xFF0EA5E9),       // Sky blue
  tertiary: Color(0xFFEC4899),        // Pink
)

Color Usage Points

• Dominant Color: Use one primary color boldly
• Sharp Accents: Use secondary color sparingly as accent
• Semantic Colors: Success=green, Error=red, Warning=yellow intuitively

Elevation & Depth

Patterns to Avoid

• Too flat designs
• Uniform elevation
• Overusing shadows

Recommended Approach

// Cards with subtle depth
Card(
  elevation: 0,
  shape: RoundedRectangleBorder(
    borderRadius: BorderRadius.circular(16),
  ),
  color: theme.colorScheme.surfaceContainerHighest,
  child: ...
)

// Soft shadow (low contrast)
BoxDecoration(
  borderRadius: BorderRadius.circular(16),
  boxShadow: [
    BoxShadow(
      color: Colors.black.withOpacity(0.04),
      blurRadius: 10,
      offset: Offset(0, 4),
    ),
  ],
)

// Glassmorphism effect
ClipRRect(
  borderRadius: BorderRadius.circular(16),
  child: BackdropFilter(
    filter: ImageFilter.blur(sigmaX: 10, sigmaY: 10),
    child: Container(
      color: Colors.white.withOpacity(0.1),
      child: ...
    ),
  ),
)

Motion & Animation

Patterns to Avoid

• Rigid UI without animations
• Excessive, scattered animations
• Inconsistent timing

Recommended Approach

// Page transition: Smooth fade+slide
PageRouteBuilder(
  transitionDuration: Duration(milliseconds: 300),
  pageBuilder: (_, __, ___) => DestinationPage(),
  transitionsBuilder: (_, animation, __, child) {
    return FadeTransition(
      opacity: animation,
      child: SlideTransition(
        position: Tween<Offset>(
          begin: Offset(0, 0.05),
          end: Offset.zero,
        ).animate(CurvedAnimation(
          parent: animation,
          curve: Curves.easeOutCubic,
        )),
        child: child,
      ),
    );
  },
)

// List items: Staggered Animation
AnimatedList + interval-based delays

// Tap feedback: Subtle scale
Transform.scale(
  scale: isPressed ? 0.98 : 1.0,
  child: AnimatedContainer(
    duration: Duration(milliseconds: 100),
    ...
  ),
)

Timing Guidelines

• Short operations (tap): 100-150ms
• Screen transitions: 250-350ms
• Complex animations: 400-600ms
• Curve: Base on easeOutCubic, easeInOutCubic

Layout & Spacing

Patterns to Avoid

• Cramped UI
• Irregular padding
• Insufficient spacing between elements

Recommended Approach

// 8px-based spacing system
const spacing = (
  xs: 4.0,
  sm: 8.0,
  md: 16.0,
  lg: 24.0,
  xl: 32.0,
  xxl: 48.0,
);

// Content area margins
Padding(
  padding: EdgeInsets.symmetric(horizontal: 20, vertical: 16),
  child: ...
)

// Card padding larger than outer
Card(
  child: Padding(
    padding: EdgeInsets.all(20),
    child: ...
  ),
)

// Gaps between elements
SizedBox(height: 16) // Between related elements
SizedBox(height: 32) // Between sections

Components

Buttons

// Primary button: Rounded corners + sufficient padding
FilledButton(
  style: FilledButton.styleFrom(
    padding: EdgeInsets.symmetric(horizontal: 24, vertical: 16),
    shape: RoundedRectangleBorder(
      borderRadius: BorderRadius.circular(12),
    ),
  ),
  child: Text('Action'),
)

// Outline button
OutlinedButton(
  style: OutlinedButton.styleFrom(
    side: BorderSide(color: theme.colorScheme.outline, width: 1.5),
    shape: RoundedRectangleBorder(
      borderRadius: BorderRadius.circular(12),
    ),
  ),
)

Input Fields

TextField(
  decoration: InputDecoration(
    filled: true,
    fillColor: theme.colorScheme.surfaceContainerHighest,
    border: OutlineInputBorder(
      borderRadius: BorderRadius.circular(12),
      borderSide: BorderSide.none,
    ),
    focusedBorder: OutlineInputBorder(
      borderRadius: BorderRadius.circular(12),
      borderSide: BorderSide(
        color: theme.colorScheme.primary,
        width: 2,
      ),
    ),
    contentPadding: EdgeInsets.symmetric(horizontal: 16, vertical: 16),
  ),
)

FAB

FloatingActionButton(
  elevation: 2,
  shape: RoundedRectangleBorder(
    borderRadius: BorderRadius.circular(16),
  ),
  child: Icon(Icons.add),
)

Background

Recommended Techniques

// Gradient background
Container(
  decoration: BoxDecoration(
    gradient: LinearGradient(
      begin: Alignment.topLeft,
      end: Alignment.bottomRight,
      colors: [
        theme.colorScheme.surface,
        theme.colorScheme.surface.withOpacity(0.95),
      ],
    ),
  ),
)

// Subtle pattern (dots, grid)
CustomPaint(
  painter: DotPatternPainter(
    color: theme.colorScheme.outline.withOpacity(0.05),
    spacing: 20,
  ),
)

Checklist

Checklist when implementing UI:

• Using fonts other than default
• Color palette has accent colors
• Appropriate margins/padding are set
• Interactions have feedback (animations)
• Component corner radii are unified (12-16px recommended)
• Text hierarchy (size/weight) is clear