Add Functionality to Finder with Action Extensions

At a glance

Project structure

Source bundle/
├── Main Application/
│   ├── AppDelegate.swift
│   ├── Base.lproj/
│   │   └── Main.storyboard
│   └── Info.plist
├── RemoveOpacityAction/
│   └── ActionViewController.swift
├── ThumbnailAction/
│   └── ActionRequestHandler.swift
├── UppercaseAction/
│   └── ActionRequestHandler.swift
├── NSImage Extensions/
│   ├── NSImage+Opaque.swift
│   ├── NSImage+SavePNG.swift
│   └── NSImage+Thumbnail.swift
├── Configuration/
│   └── SampleCode.xcconfig
└── CustomQuickActions.xcodeproj/
    ├── .xcodesamplecode.plist
    └── project.pbxproj

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 13 project/configuration file(s) and 4 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["ActionViewController"]
    N3["ActionRequestHandler"]
    N4["Cocoa APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

Main Application/AppDelegate.swift:10 — architecture anchor

@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {
}

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 AppKit.

Ownership and state

classDiagram
    ActionViewController o-- NSPopUpButton : colorPopUpButton

Ownership evidence

RemoveOpacityAction/ActionViewController.swift:14 — stored dependency or nearest verified ownership anchor

class ActionViewController: NSViewController {
    // ...
    @IBOutlet var colorPopUpButton: NSPopUpButton!
    // ...
}

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

RemoveOpacityAction/ActionViewController.swift:76 — representative execution boundary

        dispatchGroup.notify(queue: DispatchQueue.main) { [unowned self] in
            guard let context = self.extensionContext
            // ...
        }

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

Main Application/AppDelegate.swift:11 — representative type boundary

@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {
}

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

Access control

Reference code

NSImage Extensions/NSImage+Opaque.swift:12 — representative boundary

    public func opaqueImage(backgroundColor: NSColor) -> NSImage {
        // ...
            backgroundColor.setFill()
        // ...
    }

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: ActionViewController; Delegate: AppDelegate; Handler: ActionRequestHandler.
• Protocols: no local protocol declaration in the scanned source.
• Methods: send, cancel, opaqueUrl, beginRequest, createThumbnail, thumbnailUrl, opaqueImage, savePNGToDisk.
• Files: Main Application/AppDelegate.swift, RemoveOpacityAction/ActionViewController.swift, ThumbnailAction/ActionRequestHandler.swift, UppercaseAction/ActionRequestHandler.swift.

Architecture takeaways

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