Design System

Design System Rules

AppTheme Pattern

Every app MUST use a centralized theme with nested enums for Colors, Fonts, and Spacing. Do NOT use a flat enum with top-level static properties.

// REQUIRED — always use nested enums
import SwiftUI

enum AppTheme {
    enum Colors {
        static let accent = Color.blue       // one accent per app
        static let textPrimary = Color.primary
        static let textSecondary = Color.secondary
        static let background = Color(.systemBackground)
        static let surface = Color(.secondarySystemBackground)
        static let cardBackground = Color(.secondarySystemGroupedBackground)
    }

    enum Fonts {
        static let largeTitle = Font.largeTitle
        static let title = Font.title
        static let headline = Font.headline
        static let body = Font.body
        static let caption = Font.caption
    }

    enum Spacing {
        static let small: CGFloat = 8
        static let medium: CGFloat = 16
        static let large: CGFloat = 24
        static let cornerRadius: CGFloat = 12
    }
}

// FORBIDDEN — never use flat structure
enum AppTheme {
    static let accentColor = Color.blue   // ❌ wrong
    static let spacing: CGFloat = 8       // ❌ wrong
}

Reference as: AppTheme.Colors.accent, AppTheme.Fonts.headline, AppTheme.Spacing.medium

Typography

• System fonts only — use SwiftUI font styles: .largeTitle, .title, .headline, .body, .caption
• No custom fonts, no downloaded fonts
• Use AppTheme.Fonts for consistent sizing

Icons (SF Symbols)

• SF Symbols only for all icons — required for every list row, button, empty state, and tab
• Reference via Image(systemName: "symbol.name")
• Pick domain-appropriate symbols (e.g. "checkmark.circle.fill" for todos, "note.text" for notes, "heart.fill" for favorites)
• Use .symbolRenderingMode(.hierarchical) or .symbolRenderingMode(.palette) for visual depth
• No custom icon assets unless the app concept specifically requires them

Colors

• One accent color that fits the app's purpose
• Use semantic colors: .primary, .secondary, Color(.systemBackground)
• Do NOT add dark mode support, colorScheme checks, or custom dark/light color handling unless the user explicitly requests it

Spacing Standards

• 16pt standard padding (outer margins, section spacing)
• 8pt compact spacing (between related elements)
• 24pt large spacing (between major sections)
• Use AppTheme.Spacing constants throughout

Empty States

Every list or collection MUST have an empty state. Use ContentUnavailableView (iOS 17+) for a polished look:

// Required — show when collection is empty
if items.isEmpty {
    ContentUnavailableView(
        "No Notes Yet",
        systemImage: "note.text",
        description: Text("Tap + to create your first note")
    )
} else {
    // Show the list
}

For custom empty states, use a styled VStack with SF Symbol + descriptive text:

VStack(spacing: 16) {
    Image(systemName: "tray")
        .font(.system(size: 48))
        .foregroundStyle(.secondary)
    Text("Nothing here yet")
        .font(.title3)
    Text("Add your first item to get started")
        .font(.subheadline)
        .foregroundStyle(.secondary)
}

Animations

Use subtle, purposeful animations for state changes and list mutations:

// Toggle/complete actions — spring animation
withAnimation(.spring) {
    item.isComplete.toggle()
}

// List insertions/removals — combine opacity + scale
.transition(.opacity.combined(with: .scale))

// Numeric text changes
.contentTransition(.numericText())

// Filter/tab changes
.animation(.default, value: selectedFilter)

Rules:

• Always use withAnimation(.spring) for toggle/complete state changes
• Always add .transition(.opacity.combined(with: .scale)) for list add/remove
• Never add gratuitous motion that slows down interaction
• Keep animations subtle — .spring and .default curves only