ios-performance-battery-patterns

name	ios-performance-battery-patterns
description	Use when touching widgets, animations, networking configuration, or background/observer cleanup — battery and performance patterns for WidgetKit timelines, SwiftUI animations, Low Power Mode handling, URLSession config, and NotificationCenter/Task cleanup under `@Observable`.

Battery & Performance Patterns

Apply these whenever touching widgets, animations, networking, or background work.

Widgets

• Limit Timeline entries to ≤ 2 (current + one next-day refresh). More entries run the provider repeatedly and drain battery.
• Use .atEnd reload policy — let WidgetKit decide when to refresh.

Animations

• Always stop animations in .onDisappear. Animations left running off-screen still consume CPU/GPU.
• Bind repeating animations to a @State var isAnimating = false: set true in .onAppear, false in .onDisappear, and pass value: isAnimating to withAnimation.
• Use .repeatCount(N) instead of .repeatForever for attention animations.

Low Power Mode

Guard expensive operations before they start:

guard !ProcessInfo.processInfo.isLowPowerModeEnabled else { return }

Apply to: image preloading, background downloads, video prefetch, heavy sync.

Network

let config = URLSessionConfiguration.default
config.allowsConstrainedNetworkAccess = false  // respect Low Data Mode
config.allowsExpensiveNetworkAccess = false    // avoid cellular when Wi-Fi preferred
config.waitsForConnectivity = true             // queue rather than fail when offline

Observer & Task Cleanup

@Observable macro-generated storage prevents nonisolated deinit from removing NotificationCenter observers. Use reference-type boxes instead:

final class NotificationObserverBox {
    private var tokens: [NSObjectProtocol] = []
    func add(_ token: NSObjectProtocol) { tokens.append(token) }
    deinit { tokens.forEach { NotificationCenter.default.removeObserver($0) } }
}

final class TaskBox {
    private var cancel: (() -> Void)?
    func store<Success, Failure>(_ task: Task<Success, Failure>) { cancel = { task.cancel() } }
    deinit { cancel?() }
}

For MPRemoteCommandCenter: store addTarget return values; call removeTarget(nil) on each in deinit.