shareplay-activities

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

Type	Use Case
.generic	Default for custom activities
.watchTogether	Video playback
.listenTogether	Audio playback
.createTogether	Collaborative creation (drawing, editing)
.workoutTogether	Shared fitness sessions

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

State	Description
.waiting	Session exists but local participant has not joined
.joined	Local participant is actively in the session
.invalidated(reason:)	Session ended (check reason for details)

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