Sample CodeiOS 14.0+, iPadOS 14.0+, Mac Catalyst 14.0+Reviewed 2026-07-21View on Apple Developer

WWDC21 Challenge: Large Text Challenge

At a glance

Item	Summary
Purpose	Teach Dynamic Type by letting people change layout properties and inspect exercise-specific feedback.
Architecture	A code-light, single-target SwiftUI challenge organized around JSON scenarios and per-exercise observable state objects.
Main pattern	`ScenarioFeedbackProtocol` gives one feedback view a common interface over different exercise models.
Boundary	No extension, persistence layer, network service, or reusable package.

Project structure

LargeTextChallenge/
├── Models/                 # Scenario, Texture, JSON loader
├── Views/
│   ├── Scenarios/          # ExerciseOne ... ExerciseFive
│   ├── Supporting/         # AdaptiveStack and shapes
│   └── ScenarioFeedbackView.swift
└── Extensions/

Each exercise intentionally keeps its property model and view variants together.

Overall architecture

flowchart LR
    App["LargeTextChallengeApp"] --> List["ScenarioList"]
    JSON["scenarios.json"] --> Loader["load<T>()"]
    Loader --> Scenario["[Scenario]"]
    Scenario --> List
    List --> Exercise["ExerciseOne ... ExerciseFive"]
    Exercise --> VM["Exercise...Properties"]
    VM --> Feedback["ScenarioFeedbackView"]

Reference code

LargeTextChallenge/Views/ScenarioList.swift:29 — data keys select a concrete teaching view (abridged).

List(scenarioData) { scenario in
    if scenario.exercise == .textWithButton {
        NavigationLink(destination: ExerciseOne(scenario)) { ... }
    } else if scenario.exercise == .textWithImage {
        NavigationLink(destination: ExerciseThree(scenario)) { ... }
    }
}

Ownership and state

classDiagram
    ScenarioList *-- Bool : isIntroPresented
    ExerciseOne *-- ExerciseOneProperties : StateObject
    ExerciseOneProperties o-- Scenario
    ExerciseOneProperties ..|> ScenarioFeedbackProtocol
    ScenarioFeedbackView o-- ScenarioFeedbackProtocol
    ExerciseOneProperties *-- Bool : published choices

Ownership evidence

LargeTextChallenge/Views/Scenarios/ExerciseOne.swift:128 — the exercise creates and retains its observable state.

struct ExerciseOne: View {
    let scenario: Scenario?
    @StateObject private var viewModel: ExerciseOneProperties

    init(_ scenario: Scenario? = nil) {
        self.scenario = scenario
        self._viewModel = StateObject(
            wrappedValue: ExerciseOneProperties(scenario)
        )
    }
}

The exercise model is the mutation authority for choices. JSON-backed Scenario values are immutable descriptions shared by value.

Class and protocol design

Each Exercise...Properties class adopts ObservableObject and ScenarioFeedbackProtocol. The protocol exposes only results(), so ScenarioFeedbackView accepts any exercise without knowing its individual toggles (LargeTextChallenge/Views/ScenarioFeedbackView.swift:10). Views remain value types; reusable AdaptiveStack<Content> uses a generic @ViewBuilder instead of type erasure.

Access control

Symbol	Access	Rationale
Exercise `viewModel`	`private`	Only its root view creates the `StateObject` (`LargeTextChallenge/Views/Scenarios/ExerciseOne.swift:130`).
Scenario fixture globals	internal default	All exercises in the single app target read them (`LargeTextChallenge/Models/Data.swift:12`).
Exercise/property types	internal default	They are target-local teaching components.
Public/file-private API	none	No cross-module contract exists; file-level widening is unnecessary.

Logic ownership and placement

Logic	Owner	Placement reason
Bundle decoding	`Data.swift` generic loader	One small fixture-loading boundary.
Exercise routing	`ScenarioList`	The scenario key maps directly to destination views.
Choice mutation and evaluation	`Exercise...Properties`	Published choices and feedback calculation change together.
Adaptive horizontal/vertical layout	`AdaptiveStack`	Reusable layout behavior is isolated from exercise content (`LargeTextChallenge/Views/Supporting/AdaptiveStack.swift:17`).

Design patterns

Pattern	Evidence	Purpose
Data-driven exercise catalog	Codable scenarios and enum keys	Keeps copy/feedback outside view code.
Strategy protocol	`ScenarioFeedbackProtocol`	One result UI works for multiple exercise models.
Observable view model	Per-exercise property classes	Shares toggles across the menu, content, and feedback views.
Generic composition	`AdaptiveStack<Content>`	Switches layout without duplicating child content.

Naming conventions

Exercise families share numbered prefixes, making related state/menu/view types easy to scan.
Model types use nouns (Scenario, Texture); feedback outputs add Result.
Boolean properties read as decisions (allowsScrolling, stackVertically).

Architecture takeaways

Keep lesson configuration immutable and user choices in an observable owner.
A tiny protocol can unify feedback without forcing common storage.
Generic view builders are effective protocol-oriented composition for SwiftUI layout.
The code contains deliberate challenge variants; they are teaching states, not production fallback paths.

Source map

Source	Role
`LargeTextChallenge/LargeTextChallengeApp.swift:10`	App entry point
`LargeTextChallenge/Models/Scenario.swift:11`	Scenario schema
`LargeTextChallenge/Models/Data.swift:17`	Generic fixture decoder
`LargeTextChallenge/Views/ScenarioFeedbackView.swift:58`	Shared result UI
`LargeTextChallenge/Views/Scenarios/ExerciseOne.swift:13`	Observable strategy implementation
`LargeTextChallenge/Views/Supporting/AdaptiveStack.swift:43`	Adaptive composition

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