peterbamuhigire/ios-production-patterns

iOS Production Patterns

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Use When

• Production-grade iOS patterns that separate good apps from great apps — UIViewController lifecycle gotchas, sensor lifecycle management, delegate pattern implementation, keyboard dismissal, Core Data migration, UIImagePickerController dismissal...
• The task needs reusable judgment, domain constraints, or a proven workflow rather than ad hoc advice.

Do Not Use When

• The task is unrelated to ios-production-patterns or would be better handled by a more specific companion skill.
• The request only needs a trivial answer and none of this skill's constraints or references materially help.

Required Inputs

• Gather relevant project context, constraints, and the concrete problem to solve.
• Confirm the desired deliverable: design, code, review, migration plan, audit, or documentation.

Workflow

• Read this SKILL.md first, then load only the referenced deep-dive files that are necessary for the task.
• Apply the ordered guidance, checklists, and decision rules in this skill instead of cherry-picking isolated snippets.
• Produce the deliverable with assumptions, risks, and follow-up work made explicit when they matter.

Quality Standards

• Keep outputs execution-oriented, concise, and aligned with the repository's baseline engineering standards.
• Preserve compatibility with existing project conventions unless the skill explicitly requires a stronger standard.
• Prefer deterministic, reviewable steps over vague advice or tool-specific magic.

Anti-Patterns

• Treating examples as copy-paste truth without checking fit, constraints, or failure modes.
• Loading every reference file by default instead of using progressive disclosure.

Outputs

• A concrete result that fits the task: implementation guidance, review findings, architecture decisions, templates, or generated artifacts.
• Clear assumptions, tradeoffs, or unresolved gaps when the task cannot be completed from available context alone.
• References used, companion skills, or follow-up actions when they materially improve execution.

References

• Use the links and companion skills already referenced in this file when deeper context is needed.

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Expert-level, ship-it details that tutorials skip. Each pattern reflects a real production bug or App Store rejection that could have been avoided.

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1. ViewController Lifecycle — The Exact Sequence

override func viewDidLoad() {
    super.viewDidLoad()
    // Called ONCE. Wire outlets, configure appearance, set initial data.
    // Never start sensors, timers, or location here.
}

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    // Called EVERY time screen is shown.
    // Refresh data from external sources here.
    locationManager.startUpdatingLocation()
}

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    // Animation complete. Start timers here.
}

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)
    // Stop sensors BEFORE leaving. Save state.
    locationManager.stopUpdatingLocation()
}

override func viewDidDisappear(_ animated: Bool) {
    super.viewDidDisappear(animated)
    // Release non-persistent resources.
}

Critical rules:

• Start CLLocationManager, sensors, timers in viewWillAppear — never viewDidLoad
• Stop them in viewWillDisappear — never viewDidDisappear (too late for some sensors)
• Refresh data in viewWillAppear so it's current every time the screen is visible

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Additional Guidance

Extended guidance for ios-production-patterns was moved to references/skill-deep-dive.md to keep this entrypoint compact and fast to load.

Use that deep dive for:

• 2. Delegate Pattern — Full Implementation (6 Steps)
• 3. Sensor Lifecycle — Location
• 4. Camera Integration — Four Gotchas
• 5. Keyboard Dismissal
• 6. Gesture Recognizer State Guard
• 7. Core Data Lightweight Migration (Mandatory Before Any Schema Change)
• 8. Programmatic UI Constraints — Two Rules
• 9. HealthKit — Partial Permissions Pattern
• 10. Core ML on Background Thread
• 11. SwiftUI / UIKit Integration
• 12. SwiftUI vs UIKit Decision
• 13. App Store Submission Checklist
• Additional deep-dive sections continue in the reference file.