Transferring data with Watch Connectivity

At a glance

Project structure

Source bundle/
├── SimpleWatchConnectivity Watch App/
│   ├── SimpleWatchConnectivityWatchApp.swift
│   ├── AppDelegate.swift
│   ├── CommandView.swift
│   ├── ContentView.swift
│   ├── FileTransfersView.swift
│   └── UserInfoTransfersView.swift
├── SimpleWatchWidget/
│   └── SimpleWatchWidget.swift
├── SimpleWatchConnectivity/
│   ├── AppDelegate.swift
│   ├── CommandsViewController.swift
│   └── FileTransfersViewController.swift
└── Shared/
    ├── TestDataProvider.swift
    └── CommandStatus.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 11 project/configuration file(s) and 28 source declaration(s).

Overall architecture

flowchart LR
    Bundle["Sample bundle"]
    V1["SimpleWatchConnectivity Watch App"]
    V2["SimpleWatchConnectivity"]
    V3["SimpleWatchWidget"]
    Boundary["WatchConnectivity APIs"]
    Bundle --> V1
    V1 --> Boundary
    Bundle --> V2
    V2 --> Boundary
    Bundle --> V3
    V3 --> Boundary

Reference code

SimpleWatchConnectivity Watch App/SimpleWatchConnectivityWatchApp.swift:10 — architecture anchor

@main
struct SimpleWatchConnectivityWatchApp: App {
    // ...
}

Interpretation

The branches represent separate entry-bearing project variants in the downloaded bundle, not runtime calls between those variants. Each branch is intentionally collapsed at the documented framework boundary; the detailed target-local flow remains in the cited files. Ownership is claimed only where the next section cites a stored property or assignment.

Ownership and state

classDiagram
    SimpleWatchConnectivityWatchApp o-- AppDelegate : appDelegate
    SimpleEntry *-- Date : date
    SimpleEntry *-- String : timestamp
    SimpleEntry o-- UIColor : color

Ownership evidence

SimpleWatchConnectivity Watch App/SimpleWatchConnectivityWatchApp.swift:12 — stored dependency or nearest verified ownership anchor

    @WKApplicationDelegateAdaptor var appDelegate: AppDelegate

    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }

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.

Class and protocol design

Shared/TestDataProvider.swift:23 — representative type boundary

protocol TestDataProvider {
    // ...
}

The source explicitly defines local protocol relationships: CommandView → TestDataProvider, CommandView → SessionCommands, CommandsViewController → TestDataProvider, CommandsViewController → SessionCommands, WCSessionUserInfoTransfer → SessionTransfer, WCSessionFileTransfer → SessionTransfer.

Access control

Reference code

Shared/FileTransferObservers.swift:17 — representative boundary

    private var fileTransferObervations = [WCSessionFileTransfer: NSKeyValueObservation]()
    private(set) var progresssDescriptions = [WCSessionFileTransfer: String]()

    private var observations: [NSKeyValueObservation] {
        return Array(fileTransferObervations.values)
    }

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

Main application flow

A reply-bearing message crosses the local command surface, Watch Connectivity, the peer delegate, and main-queue notifications on both devices.

sequenceDiagram
    actor User
    participant View as CommandView
    participant Commands as SessionCommands
    participant Local as Local WCSession
    participant Peer as Peer WCSession
    participant Delegate as SessionDelegator
    participant Events as NotificationCenter
    User->>View: Send message
    View->>Commands: sendMessage(payload)
    Commands->>Local: sendMessage(replyHandler, errorHandler)
    Local->>Peer: Deliver message
    Peer-->>Delegate: didReceiveMessage(replyHandler)
    Delegate->>Events: Post received status on main queue
    Delegate-->>Peer: replyHandler(message)
    Peer-->>Local: Deliver reply asynchronously
    Local-->>Commands: replyHandler(replyMessage)
    Commands->>Events: Post replied status on main queue
    Events-->>View: Refresh command status

Reference code

Shared/SessionCommands.swift:47 — the sender publishes both the initial sent state and the asynchronous reply or error state.

func sendMessage(_ message: [String: Any]) {
    var commandStatus = CommandStatus(command: .sendMessage, phrase: .sent)
    commandStatus.timedColor = TimedColor(message)
    guard WCSession.default.activationState == .activated else {
        return handleSessionUnactivated(with: commandStatus)
    }
    WCSession.default.sendMessage(message, replyHandler: { replyMessage in
        commandStatus.phrase = .replied
        commandStatus.timedColor = TimedColor(replyMessage)
        self.postNotificationOnMainQueueAsync(name: .dataDidFlow, object: commandStatus)
    }, errorHandler: { error in
        commandStatus.phrase = .failed
        commandStatus.errorMessage = error.localizedDescription
        self.postNotificationOnMainQueueAsync(name: .dataDidFlow, object: commandStatus)
    })
    postNotificationOnMainQueueAsync(name: .dataDidFlow, object: commandStatus)
}

Shared/SessionDelegator.swift:48 — the receiver records the message and echoes it through the supplied reply callback.

func session(_ session: WCSession, didReceiveMessage message: [String: Any]) {
    var commandStatus = CommandStatus(command: .sendMessage, phrase: .received)
    commandStatus.timedColor = TimedColor(message)
    postNotificationOnMainQueueAsync(name: .dataDidFlow, object: commandStatus)
}

func session(_ session: WCSession, didReceiveMessage message: [String: Any], replyHandler: @escaping ([String: Any]) -> Void) {
    self.session(session, didReceiveMessage: message)
    replyHandler(message)
}

Naming conventions

• Types: App: SimpleWatchConnectivityWatchApp; Command: Command; Controller: CommandsViewController, FileTransfersViewController, MainViewController, UserInfoTransfersViewController; Delegate: AppDelegate; Provider: Provider, TestDataProvider; View: CommandView, ContentView, FileTransfersView, SimpleWatchWidgetEntryView, UserInfoTransfersView.
• Protocols: TestDataProvider, SessionCommands, SessionTransfer.
• Methods: placeholder, getSnapshot, getTimeline, application, timedColor, completeBackgroundTasks, handle, outstandingTransferCount.
• Files: SimpleWatchConnectivity Watch App/SimpleWatchConnectivityWatchApp.swift, SimpleWatchWidget/SimpleWatchWidget.swift, SimpleWatchConnectivity/AppDelegate.swift, Shared/TestDataProvider.swift, Shared/CommandStatus.swift, SimpleWatchConnectivity Watch App/AppDelegate.swift.

Architecture takeaways

• SimpleWatchConnectivityWatchApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches WatchConnectivity, UIKit, SwiftUI, WidgetKit 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