dat-conventions

DAT SDK Conventions (Android)

Quick Reference

Architecture

The SDK is organized into four public modules:

• mwdat-core: Registration, permissions, devices, and session creation
• mwdat-camera: Camera capability, video frames, and photo capture
• mwdat-display: Display capability, display UI components, icons, images, buttons, and video
• mwdat-mockdevice: MockDeviceKit for testing without hardware

Initialization and session setup

DeviceSession.start() is fire-and-forget and returns Unit; capabilities can only be attached once the session reports DeviceSessionState.STARTED.

Wearables.initialize(context)

Wearables.createSession(AutoDeviceSelector()).fold(
    onSuccess = { session ->
        lifecycleScope.launch {
            session.state.collect { state ->
                if (state == DeviceSessionState.STARTED) {
                    session.addCamera(StreamConfiguration()).fold(
                        onSuccess = { camera ->
                            camera.stream.start().onFailure { error, _ ->
                                showError(error.description)
                            }
                        },
                        onFailure = { error, _ -> showError(error.description) },
                    )
                }
            }
        }
        lifecycleScope.launch {
            session.errors.collect { error -> showError(error.description) }
        }
        session.start()
    },
    onFailure = { error, _ -> showError(error.description) },
)

Kotlin patterns

• Use DatResult<T, E> for typed success and failure handling
• Prefer fold, onSuccess, and the two-parameter onFailure { error, cause -> } overload, which hands you the typed DatError with a description
• getOrElse { } receives a raw Throwable, not a typed DatError, so it cannot read error.description
• Observe state with StateFlow and Flow
• Create a DeviceSession first, then attach capabilities such as Camera or Display after it reaches STARTED
• Keep frame handling off the main thread when doing heavier processing

Error handling

Wearables.checkPermissionStatus(Permission.CAMERA)
    .onSuccess { status -> /* handle status */ }
    .onFailure { error, _ -> /* handle error */ }

Avoid getOrThrow() in user-facing samples. Surface typed errors from DatResult instead.

Naming conventions

Key types

• Wearables — SDK entry point
• DeviceSession — lifecycle for an interaction with a linked device
• Camera — camera capability attached to a session
• Stream — video stream accessed through camera.stream
• Display — display capability attached to a session
• StreamConfiguration — video quality, frame rate, and compression configuration
• MockDeviceKit — simulated device environment for testing

Live docs search

If your editor supports remote MCP servers, connect https://mcp.developer.meta.com/wearables and use search_dat_docs for current DAT setup, session lifecycle, camera streaming, MockDeviceKit, permissions, and exact API symbols. This public docs server does not require authentication; do not configure tokens, OAuth, or custom authorization headers for it.

See the dat-docs-mcp skill for client setup and troubleshooting. Use llms.txt when your tool only supports static reference context.

Testing with MockDeviceKit

val mockDeviceKit = MockDeviceKit.getInstance(context)
mockDeviceKit.enable()
mockDeviceKit.pairGlasses(GlassesModel.RAYBAN_META).fold(
    onSuccess = { device -> onMockDevicePaired(device) },
    onFailure = { error, _ -> showError(error.description) },
)

Use MockDeviceKit to drive registration, device availability, streaming media, and permission scenarios without physical hardware.

Common pitfalls

• Do not call SDK APIs before Wearables.initialize(context)
• Do not call addCamera(...) or addDisplay() immediately after session.start(); wait for DeviceSessionState.STARTED
• Do not assume a session implies streaming or display access; capabilities are attached separately
• Do not ignore DatResult failures from createSession, start, addCamera, addDisplay, or capturePhoto
• Do not reuse terminally stopped sessions, cameras, or streams

Links

• Android API reference
• Developer documentation
• GitHub repository