Customizing collection view layouts

At a glance

Project structure

Source bundle/
├── ImageFeed/
│   ├── AppDelegate.swift
│   ├── Controls/
│   │   └── AvatarView.swift
│   ├── FeedViewController.swift
│   ├── FriendsViewController.swift
│   ├── Layouts/
│   │   ├── MosaicLayout.swift
│   │   └── ColumnFlowLayout.swift
│   ├── Model/
│   │   └── Person.swift
│   ├── Cells/
│   │   ├── MosaicCell.swift
│   │   └── PersonCell.swift
│   └── Utilities/
│       └── Utilities.swift
├── Configuration/
│   └── SampleCode.xcconfig
└── ImageFeed.xcodeproj/
    └── .xcodesamplecode.plist

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 6 project/configuration file(s) and 11 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["FeedViewController"]
    N3["UIKit APIs"]
    N1 --> N2
    N2 --> N3

Reference code

ImageFeed/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 UIKit.

Ownership and state

classDiagram
    AppDelegate o-- UIWindow : window
    AvatarView *-- UIImageView : avatarImgView
    FeedViewController *-- AvatarView : avatarView
    FriendsViewController *-- ColumnFlowLayout : flowLayout

Ownership evidence

ImageFeed/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.

@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

ImageFeed/FeedViewController.swift:49 — representative execution boundary

                DispatchQueue.main.async {
                    // Reload collection view once we've determined our Photos permissions.
                    self.collectionView.reloadData()
                }

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

ImageFeed/AppDelegate.swift:11 — representative type boundary

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

}

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

Access control

Reference code

ImageFeed/FeedViewController.swift:101 — representative boundary

    private func displayPhotoAccessDeniedAlert() {
        // ...
                                                message: message,
        // ...
    }

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: FeedViewController, FriendsViewController; Delegate: AppDelegate; View: AvatarView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: layoutSubviews, viewDidLoad, viewWillAppear, collectionView, displayPhotoAccessDeniedAlert, prepare, updateButtonTapped, didRefresh.
• Files: ImageFeed/AppDelegate.swift, ImageFeed/Controls/AvatarView.swift, ImageFeed/FeedViewController.swift, ImageFeed/FriendsViewController.swift, ImageFeed/Layouts/MosaicLayout.swift, ImageFeed/Model/Person.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches UIKit, Photos 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