Adopting iOS Dark Mode

At a glance

Project structure

AdoptingDarkMode/
├── AppDelegate.swift
├── Before1MoreViewController.swift
├── After2MoreViewController.swift
├── Before1SlowDrawingViewController.swift
├── After2SlowDrawingViewController.swift
├── AlwaysDarkViewController.swift
├── Base.lproj/Main.storyboard
└── Assets.xcassets/

Structure observations

• Paired filenames make adoption changes directly comparable.
• Dynamic named colors/images live in the asset catalog; programmatic system colors/materials remain in the after controller.
• Only the slow-drawing example owns asynchronous state and trait-change regeneration.

Overall architecture

flowchart LR
    Storyboard["Storyboard catalog"] --> Before["Before1 examples"]
    Storyboard --> After["After2 examples"]
    Storyboard --> Forced["AlwaysDarkViewController"]
    Before --> Fixed["Fixed colors and light blur"]
    After --> Dynamic["System colors, named assets, materials"]
    After --> Traits["UITraitCollection"]
    Traits --> Drawing["Trait-aware background renderer"]
    Forced --> Override["overrideUserInterfaceStyle"]

Reference code

AdoptingDarkMode/After2SlowDrawingViewController.swift:45 — the adopted path captures the current traits before leaving the main thread and resolves dynamic colors under that context.

let colors: [UIColor] = [.systemBackground,
                         .secondarySystemBackground,
                         .gray,
                         UIColor(named: "LightAndDarkHeaderColor")!]
let traitCollection = self.traitCollection

DispatchQueue.global(qos: .userInitiated).async {
    var image: UIImage?
    traitCollection.performAsCurrent {
        image = self.createImage(size, colors)
    }
    DispatchQueue.main.async { self.resultImageView.image = image }
}

Interpretation

The sample is organized for learning, not reuse. Architecture is the comparison: the after screens move appearance selection to semantic assets/UIKit traits and explicitly carry those traits into off-main rendering.

Ownership and state

classDiagram
    Storyboard *-- UIViewController : creates examples
    After2SlowDrawingViewController o-- UIImageView : outlet
    After2SlowDrawingViewController o-- UIActivityIndicatorView : outlet
    After2SlowDrawingViewController --> UITraitCollection : captures value
    BackgroundQueue --> UIImage : creates
    MainQueue --> UIImageView : assigns
    AlwaysDarkViewController --> UIUserInterfaceStyle : overrides subtree

Ownership evidence

AdoptingDarkMode/After2SlowDrawingViewController.swift:15 — the drawing screen keeps only storyboard outlets; render inputs/results are local to each run.

@IBOutlet var resultImageView: UIImageView!
@IBOutlet var activityIndicator: UIActivityIndicatorView!

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    performSlowDrawing()
}

Class and protocol design

No local protocol or cross-screen service exists; each controller is an isolated API demonstration.

Access control

Reference code

AdoptingDarkMode/AlwaysDarkViewController.swift:10 — style ownership is scoped to the controller, but the type itself remains target-internal.

class AlwaysDarkViewController: UIViewController {
    override init(nibName: String?, bundle: Bundle?) {
        super.init(nibName: nibName, bundle: bundle)
        overrideUserInterfaceStyle = .dark
    }

    required init?(coder: NSCoder) {
        super.init(coder: coder)
        overrideUserInterfaceStyle = .dark
    }
}

Logic ownership and placement

Design patterns

Naming conventions

• Before1 and After2 prefixes encode teaching order and migration state.
• SlowDrawing names the concurrency case; More collects ordinary view/material examples.
• AlwaysDarkViewController names the behavior rather than a domain screen.

Architecture takeaways

• Treat this source as a migration comparison, not a reusable multi-screen app design.
• Let semantic colors, named assets, and materials resolve appearance automatically.
• Capture a trait collection before background rendering and install results on the main queue.
• Scope forced appearance to the narrowest controller subtree.

Source map

• Official Apple documentation