iOS 15 SharePlay - Build a Group Drawing App

Create an Xcode project for an iOS app named GroupDraw, selecting the app template, storyboard interface, and Swift language, then choose a save location.

Add a drawing canvas with PencilKit to enable any-input drawing in the iOS 15 SharePlay app. Configure PKCanvasView and auto layout to cover the screen.

Add a PKToolPicker to the drawing app to provide brushes, pens, erasers, and colors, with the canvas view as the first responder and observers for tool changes.

Add a clear button in the navigation bar to reset the drawing canvas by assigning a new PKDrawing to canvasView, via handleClearCanvas.

Add undo and redo buttons to the drawing app, implement handleUndoStroke and handleRedoStroke, track removed strokes with removedStrokes, and enable or disable buttons based on canvas activity using PKCanvasViewDelegate methods.

Explore SharePlay, iOS 15's feature for synchronized experiences on a FaceTime call, powered by the Group Activities framework, enabling music playback, video streaming, and screen sharing with others.

Explore the group activities framework powering SharePlay, enabling app-specific activities and a synchronized FaceTime canvas. Ensure end-to-end encryption and enable group activities in Xcode with an active Apple Developer Program.

Define a custom group activity by adding the Group Activities entitlement, implementing GroupActivity with metadata in GroupDrawActivity, and wiring session management for a shared drawing experience on iOS 15.

Add start and end group activity buttons as right bar button items, implement the start and end handlers, and move undo and redo to the left bar button items.

Configure and manage group sessions with the group activities framework to synchronize drawing activity across devices and use group session messenger to transmit drawing data between participants.

Configure group session by initializing a GroupSessionMessenger, subscribing to activeParticipants, and joining the session, and define GroupDrawMessageType with join, stroke, undo, and clear to exchange canvas and drawing updates.

Send the current drawing canvas to new participants and on each new stroke using GroupSessionMessenger, by configuring the group session and sending a PKDrawing derived from the last stroke.

Learn to receive data from other participants using GroupSessionMessenger, iterate messages asynchronously, and handle join, draw, undo, and clear to update the canvas and send the current canvas state.

Implement and test group activity in a SharePlay drawing app by configuring a session, awaiting prepareForActivation(), handling activation results, and starting or ending the activity via a FaceTime call.

Implement undo, redo, and clear for a group canvas by sending undo, redo, and clear messages to all participants via GroupSessionMessenger.