Track performance by app state using MetricKit

At a glance

Project structure

Source bundle/
└── MetricKit-Sample/
    ├── MetricKitSampleApp.swift
    ├── View Models/
    │   ├── DashboardViewModel.swift
    │   └── ExpenseReportViewModel.swift
    ├── ReportableMetadata.swift
    └── Views/
        ├── DocumentCameraView.swift
        ├── MainTabView.swift
        ├── CrashReportAnnotationView.swift
        ├── Dashboard/
        │   └── DashboardView.swift
        └── Expenses/
            ├── ExpenseCardView.swift
            ├── ExpenseDetailView.swift
            ├── ExpenseFormView.swift
            └── ExpenseRowView.swift

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: Swift.
• The verified tree contains 5 project/configuration file(s) and 39 source declaration(s).

Overall architecture

flowchart LR
    N1["MetricKitSampleApp"]
    N2["MainTabView"]
    N3["DashboardViewModel"]
    N4["SwiftUI / SwiftData APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

MetricKit-Sample/MetricKitSampleApp.swift:11 — architecture anchor

@main
struct MetricKitSampleApp: App {
    // ...
    private let metricsCollector = MetricsCollector()
    // ...
}

Interpretation

The arrows summarize the source-visible entry, role-named types or folders, and framework direction; when nodes come from structural folders, the sequence is a high-level interpretation rather than proof that every adjacent node calls the next. Ownership is claimed only where the next section cites a stored property or assignment. The diagram is intentionally limited to the dominant path into MetricKit.

Ownership and state

classDiagram
    MetricKitSampleApp *-- MetricsCollector : metricsCollector
    CategorySpend o-- ExpenseCategory : category
    CategorySpend *-- Double : total
    CategoryAverage o-- ExpenseCategory : category

Ownership evidence

MetricKit-Sample/MetricKitSampleApp.swift:16 — stored dependency or nearest verified ownership anchor

@main
struct MetricKitSampleApp: App {
    // ...
    private let metricsCollector = MetricsCollector()
    // ...
}

Composition arrows indicate a source-visible construction expression or locally owned value state; aggregation means the owner stores or receives a dependency without proving exclusive lifetime ownership.

Concurrency, scheduling, and thread safety

Evidence limit: actor isolation, async/await, or Task creation does not by itself prove background-thread execution; Sendable conformance alone does not prove thread-safe mutation.

@MainActor/MainActor.run, DispatchQueue.main, and RunLoop.main are reported as distinct isolation, queue, and event-loop mechanisms. A plain Task is kept separate from Task.detached; neither is labeled as a background thread.

Reference code

MetricKit-Sample/MetricsCollector.swift:21 — representative execution boundary

@MainActor
@Observable
class MetricsCollector {
    private let logger = Logger.metricsCollector
    // ...
}

State propagation, frameworks, and dependencies

Evidence limit: an import proves a source-level compilation dependency at the cited line; it does not prove runtime use, architectural adoption, or whether a Swift package is a direct application dependency.

receive(on:) describes downstream delivery scheduling, while subscribe(on:) describes upstream subscription/request/cancel scheduling. An import Combine alone establishes neither behavior nor a Store, reducer, Redux, or other application architecture.

Class and protocol design

MetricKit-Sample/MetricKitSampleApp.swift:12 — representative type boundary

@main
struct MetricKitSampleApp: App {
    // ...
    private let metricsCollector = MetricsCollector()
    // ...
}

No local protocol conformance is claimed as protocol-oriented design; external framework conformances are listed only as dependencies.

Access control

Reference code

MetricKit-Sample/DataContainer.swift:26 — representative boundary

    private static let defaultContainer: ModelContainer = {
        // ...
            let modelContainer = try ModelContainer(for: ExpenseReport.self)
        // ...
    }()

Swift declarations without a modifier are internal; explicit private, fileprivate, private(set), public, or open entries above are interpreted by language semantics. Objective-C/C samples instead rely on header and implementation boundaries, which are not equivalent to Swift lexical privacy.

Logic ownership and placement

Design patterns

Naming conventions

• Types: App: MetricKitSampleApp; Coordinator: Coordinator; View: CrashReportAnnotationView, DashboardView, DocumentCameraView, ExpenseCardView, ExpenseDetailView; ViewModel: DashboardViewModel, ExpenseReportViewModel.
• Protocols: no local protocol declaration in the scanned source.
• Methods: computeSpendingValues, didScanImage, clearPendingImage, addReport, submitReport, revertToDraft, deleteExpenses, addExpense.
• Files: MetricKit-Sample/MetricKitSampleApp.swift, MetricKit-Sample/View Models/DashboardViewModel.swift, MetricKit-Sample/View Models/ExpenseReportViewModel.swift, MetricKit-Sample/Views/DocumentCameraView.swift, MetricKit-Sample/Views/MainTabView.swift, MetricKit-Sample/Views/CrashReportAnnotationView.swift.

Architecture takeaways

• MetricKitSampleApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, SwiftData, StateReporting, Charts through a deliberately small high-level chain; the detailed API graph remains inside the cited implementation files.
• Stored-property evidence identifies lifecycle collaboration; it does not by itself prove exclusive object ownership.
• Access-control conclusions separate verified language visibility from the likely design rationale.
• The source does not justify labeling the design protocol-oriented.

Source map

• Official Apple documentation