shareplay-activities（分享游戏活动）

GroupActivities / SharePlay

Build shared real-time experiences using the GroupActivities framework. SharePlay connects people over FaceTime or iMessage, synchronizing media playback, app state, or custom data. Targets Swift 6.3 / iOS 26+.

Contents

• Setup
• Defining a GroupActivity
• Session Lifecycle
• Sending and Receiving Messages
• Coordinated Media Playback
• Starting SharePlay from Your App
• GroupSessionJournal: File Transfer
• Common Mistakes
• Review Checklist
• References

Setup

Entitlements

Add the Group Activities entitlement to your app:

<key>com.apple.developer.group-session</key>
<true/>

Info.plist

For apps that start SharePlay without a FaceTime call (iOS 17+), add:

<key>NSSupportsGroupActivities</key>
<true/>

Checking Eligibility

import GroupActivities

let observer = GroupStateObserver()

// Check if a FaceTime call or iMessage group is active
if observer.isEligibleForGroupSession {
    showSharePlayButton()
}

Observe changes reactively:

for await isEligible in observer.$isEligibleForGroupSession.values {
    showSharePlayButton(isEligible)
}

Defining a GroupActivity

Conform to GroupActivity and provide metadata:

import GroupActivities
import CoreTransferable

struct WatchTogetherActivity: GroupActivity {
    let movieID: String
    let movieTitle: String

    var metadata: GroupActivityMetadata {
        var meta = GroupActivityMetadata()
        meta.title = movieTitle
        meta.type = .watchTogether
        meta.fallbackURL = URL(string: "https://example.com/movie/\(movieID)")
        return meta
    }
}

Activity Types

The activity struct must conform to Codable so the system can transfer it between devices.

Session Lifecycle

Listening for Sessions

Set up a long-lived task to receive sessions when another participant starts the activity:

@Observable
@MainActor
final class SharePlayManager {
    private var session: GroupSession<WatchTogetherActivity>?
    private var messenger: GroupSessionMessenger?
    private var tasks = TaskGroup()

    func observeSessions() {
        Task {
            for await session in WatchTogetherActivity.sessions() {
                self.configureSession(session)
            }
        }
    }

    private func configureSession(
        _ session: GroupSession<WatchTogetherActivity>
    ) {
        self.session = session
        self.messenger = GroupSessionMessenger(session: session)

        // Observe session state changes
        Task {
            for await state in session.$state.values {
                handleState(state)
            }
        }

        // Observe participant changes
        Task {
            for await participants in session.$activeParticipants.values {
                handleParticipants(participants)
            }
        }

        // Join the session
        session.join()
    }
}

Session States

Handling State Changes

private func handleState(_ state: GroupSession<WatchTogetherActivity>.State) {
    switch state {
    case .waiting:
        print("Waiting to join")
    case .joined:
        print("Joined session")
        loadActivity(session?.activity)
    case .invalidated(let reason):
        print("Session ended: \(reason)")
        cleanUp()
    @unknown default:
        break
    }
}

private func handleParticipants(_ participants: Set<Participant>) {
    print("Active participants: \(participants.count)")
}

Leaving and Ending

// Leave the session (other participants continue)
session?.leave()

// End the session for all participants
session?.end()

Sending and Receiving Messages

Use GroupSessionMessenger to sync app state between participants.

Defining Messages

Messages must be Codable:

struct SyncMessage: Codable {
    let action: String
    let timestamp: Date
    let data: [String: String]
}

Sending

func sendSync(_ message: SyncMessage) async throws {
    guard let messenger else { return }

    try await messenger.send(message, to: .all)
}

// Send to specific participants
try await messenger.send(message, to: .only(participant))

Receiving

func observeMessages() {
    guard let messenger else { return }

    Task {
        for await (message, context) in messenger.messages(of: SyncMessage.self) {
            let sender = context.source
            handleReceivedMessage(message, from: sender)
        }
    }
}

Delivery Modes

// Reliable (default) -- guaranteed delivery, ordered
let reliableMessenger = GroupSessionMessenger(
    session: session,
    deliveryMode: .reliable
)

// Unreliable -- faster, no guarantees (good for frequent position updates)
let unreliableMessenger = GroupSessionMessenger(
    session: session,
    deliveryMode: .unreliable
)

Use .reliable for state-changing actions (play/pause, selections). Use .unreliable for high-frequency ephemeral data (cursor positions, drawing strokes).

Coordinated Media Playback

For video/audio, use AVPlaybackCoordinator with AVPlayer:

import AVFoundation
import GroupActivities

func configurePlayback(
    session: GroupSession<WatchTogetherActivity>,
    player: AVPlayer
) {
    // Connect the player's coordinator to the session
    let coordinator = player.playbackCoordinator
    coordinator.coordinateWithSession(session)
}

Once connected, play/pause/seek actions on any participant's player are automatically synchronized to all other participants. No manual message passing is needed for playback controls.

Handling Playback Events

// Notify participants about playback events
let event = GroupSessionEvent(
    originator: session.localParticipant,
    action: .play,
    url: nil
)
session.showNotice(event)

Starting SharePlay from Your App

Using GroupActivitySharingController (UIKit)

import GroupActivities
import UIKit

func startSharePlay() async throws {
    let activity = WatchTogetherActivity(
        movieID: "123",
        movieTitle: "Great Movie"
    )

    switch await activity.prepareForActivation() {
    case .activationPreferred:
        // Already in a FaceTime/iMessage session — activate directly
        _ = try await activity.activate()

    case .activationDisabled:
        // SharePlay is disabled or unavailable
        print("SharePlay not available")

    case .cancelled:
        break

    @unknown default:
        break
    }
}

When no conversation is active (i.e., isEligibleForGroupSession is false), use GroupActivitySharingController to let the user pick contacts first:

let controller = try GroupActivitySharingController(activity)
present(controller, animated: true)

For ShareLink (SwiftUI) and direct activity.activate() patterns, see references/shareplay-patterns.md.

GroupSessionJournal: File Transfer

For large data (images, files), use GroupSessionJournal instead of GroupSessionMessenger (which has a size limit):

import GroupActivities

let journal = GroupSessionJournal(session: session)

// Upload a file
let attachment = try await journal.add(imageData)

// Observe incoming attachments
Task {
    for await attachments in journal.attachments {
        for attachment in attachments {
            let data = try await attachment.load(Data.self)
            handleReceivedFile(data)
        }
    }
}

Common Mistakes

DON'T: Forget to call session.join()

// WRONG -- session is received but never joined
for await session in MyActivity.sessions() {
    self.session = session
    // Session stays in .waiting state forever
}

// CORRECT -- join after configuring
for await session in MyActivity.sessions() {
    self.session = session
    self.messenger = GroupSessionMessenger(session: session)
    session.join()
}

DON'T: Forget to leave or end sessions

// WRONG -- session stays alive after the user navigates away
func viewDidDisappear() {
    // Nothing -- session leaks
}

// CORRECT -- leave when the view is dismissed
func viewDidDisappear() {
    session?.leave()
    session = nil
    messenger = nil
}

DON'T: Assume all participants have the same state

// WRONG -- broadcasting state without handling late joiners
func onJoin() {
    // New participant has no idea what the current state is
}

// CORRECT -- send full state to new participants
func handleParticipants(_ participants: Set<Participant>) {
    let newParticipants = participants.subtracting(knownParticipants)
    for participant in newParticipants {
        Task {
            try await messenger?.send(currentState, to: .only(participant))
        }
    }
    knownParticipants = participants
}

DON'T: Use GroupSessionMessenger for large data

// WRONG -- messenger has a per-message size limit
let largeImage = try Data(contentsOf: imageURL)  // 5 MB
try await messenger.send(largeImage, to: .all)    // May fail

// CORRECT -- use GroupSessionJournal for files
let journal = GroupSessionJournal(session: session)
try await journal.add(largeImage)

DON'T: Send redundant messages for media playback

// WRONG -- manually syncing play/pause when using AVPlayer
func play() {
    player.play()
    try await messenger.send(PlayMessage(), to: .all)
}

// CORRECT -- let AVPlaybackCoordinator handle it
player.playbackCoordinator.coordinateWithSession(session)
player.play()  // Automatically synced to all participants

DON'T: Observe sessions in a view that gets recreated

// WRONG -- each time the view appears, a new listener is created
struct MyView: View {
    var body: some View {
        Text("Hello")
            .task {
                for await session in MyActivity.sessions() { }
            }
    }
}

// CORRECT -- observe sessions in a long-lived manager
@Observable
final class ActivityManager {
    init() {
        Task {
            for await session in MyActivity.sessions() {
                configureSession(session)
            }
        }
    }
}

Review Checklist

• Group Activities entitlement (com.apple.developer.group-session) added
• GroupActivity struct is Codable with meaningful metadata
• sessions() observed in a long-lived object (not a SwiftUI view body)
• session.join() called after receiving and configuring the session
• session.leave() called when the user navigates away or dismisses
• GroupSessionMessenger created with appropriate deliveryMode
• Late-joining participants receive current state on connection
• $state and $activeParticipants publishers observed for lifecycle changes
• GroupSessionJournal used for large file transfers instead of messenger
• AVPlaybackCoordinator used for media sync (not manual messages)
• GroupStateObserver.isEligibleForGroupSession checked before showing SharePlay UI
• prepareForActivation() called before presenting sharing controller
• Session invalidation handled with cleanup of messenger, journal, and tasks

References

• Extended patterns (collaborative canvas, spatial Personas, custom templates): references/shareplay-patterns.md
• GroupActivities framework
• GroupActivity protocol
• GroupSession
• GroupSessionMessenger
• GroupSessionJournal
• GroupStateObserver
• GroupActivitySharingController
• Defining your app's SharePlay activities
• Presenting SharePlay activities from your app's UI
• Synchronizing data during a SharePlay activity