ios-patterns

iOS SwiftUI Patterns

A collection of SwiftUI conventions that keep code consistent, localizable, and resilient to edge cases. Apply these patterns to any iOS/macOS SwiftUI project. See references/ for in-depth guides.

1. Localization (i18n)

Use String Catalog (.xcstrings) — not Localizable.strings — for all user-facing text. Reference: references/i18n-guide.md.

// In a View: LocalizedStringKey is inferred
Text("welcome_message")
Text("greeting \(username)")

// In a ViewModel or non-View context, use String(localized:)
let message = String(localized: "error_network")
let formatted = String(localized: "items_count \(count)")

Key naming

Use snake_case, grouped by feature: home_title, settings_notification_enabled, error_network_unavailable. Embed parameters in the key: "profile_welcome \(name)", "cart_items_count \(count)".

Avoid

Text("Welcome")                                    // ❌ hard-coded
let title: LocalizedStringKey = "welcome"          // ❌ only works in Views
let title = String(localized: "welcome")           // ✅ works anywhere

2. Date & Time Localization

Never hard-code format strings like "M/d" or "MM/dd". Different locales order date components differently (US: 12/13, AU/UK: 13/12, TW: 12/13). Use setLocalizedDateFormatFromTemplate so the system picks the correct order.

Centralize formatting behind one utility (e.g. LocalizedDateFormatter) that vends cached DateFormatters keyed by template:

enum LocalizedDateStyle {
    case monthDayNumeric         // "Md"       → 12/13 or 13/12
    case monthDayAbbreviated     // "MMMd"     → Dec 13 / 13 Dec / 12月13日
    case yearMonthDayAbbreviated // "yMMMd"    → Dec 13, 2025
    case yearMonthDayFull        // "yMMMMd"   → December 13, 2025
    // ...
}

let text = LocalizedDateFormatter.string(from: date, style: .monthDayAbbreviated)

Rules

• Preserve script variants when constructing Locale (e.g. zh-Hant vs zh-Hans) so Traditional and Simplified Chinese users see the right format.
• DateFormatter is not thread-safe — shared cached formatters are main-thread only. Background threads must create their own instance.
• Storage/API/logs use fixed ISO formats (yyyy-MM-dd, HH:mm) — not localized.