IceCreamBuilder: Building an iMessage Extension

At a glance

Project structure

Source bundle/
├── IceCreamBuilder/
│   ├── AppDelegate.swift
│   └── ViewController.swift
└── IceCreamBuilderMessagesExtension/
    ├── IceCreamsViewController.swift
    ├── BuildIceCreamViewController.swift
    ├── CompletedIceCreamViewController.swift
    ├── IceCreamPart.swift
    ├── IceCreamView.swift
    ├── MessagesViewController.swift
    ├── IceCream+Image.swift
    ├── IceCream.swift
    ├── IceCreamAddCell.swift
    └── IceCreamCell.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 8 project/configuration file(s) and 23 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["BuildIceCreamViewController"]
    N3["Messages APIs"]
    N1 --> N2
    N2 --> N3

Reference code

IceCreamBuilder/AppDelegate.swift:10 — architecture anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?
}

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 Messages.

Ownership and state

classDiagram
    AppDelegate o-- UIWindow : window
    IceCreamsViewController o-- IceCreamsViewControllerDelegate : delegate
    IceCreamsViewController *-- Array : items
    BuildIceCreamViewController o-- BuildIceCreamViewControllerDelegate : delegate

Ownership evidence

IceCreamBuilder/AppDelegate.swift:13 — stored dependency or nearest verified ownership anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?
}

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.

No source-visible execution, scheduling, or synchronization boundary was found in the indexed source.

@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.

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

IceCreamBuilderMessagesExtension/IceCreamsViewController.swift:111 — representative type boundary

protocol IceCreamsViewControllerDelegate: AnyObject {

    /// Called when a user choses to add a new `IceCream` in the `IceCreamsViewController`.

    func iceCreamsViewControllerDidSelectAdd(_ controller: IceCreamsViewController)
}

The source explicitly defines local protocol relationships: Topping → IceCreamPart, Topping → QueryItemRepresentable, Scoops → IceCreamPart, Scoops → QueryItemRepresentable, Base → IceCreamPart, Base → QueryItemRepresentable.

Access control

Reference code

IceCreamBuilderMessagesExtension/BuildIceCreamViewController.swift:38 — representative boundary

    fileprivate var iceCreamParts = [IceCreamPart]() {
        // ...
            guard isViewLoaded else { return }
        // ...
    }

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: Controller: BuildIceCreamViewController, CompletedIceCreamViewController, IceCreamsViewController, MessagesViewController, ViewController; Delegate: AppDelegate, BuildIceCreamViewControllerDelegate, IceCreamsViewControllerDelegate; View: IceCreamView.
• Protocols: IceCreamsViewControllerDelegate, BuildIceCreamViewControllerDelegate, IceCreamPart, QueryItemRepresentable.
• Methods: collectionView, dequeueIceCreamCell, dequeueIceCreamAddCell, iceCreamsViewControllerDidSelectAdd, viewDidLoad, viewDidLayoutSubviews, didTapSelect, buildIceCreamViewController.
• Files: IceCreamBuilder/AppDelegate.swift, IceCreamBuilderMessagesExtension/IceCreamsViewController.swift, IceCreamBuilderMessagesExtension/BuildIceCreamViewController.swift, IceCreamBuilder/ViewController.swift, IceCreamBuilderMessagesExtension/CompletedIceCreamViewController.swift, IceCreamBuilderMessagesExtension/IceCreamPart.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches UIKit, Messages 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.
• Local protocol relationships provide an explicit substitution boundary.

Source map

• Official Apple documentation