dat-conventions

用於 DAT SDK Android 開發的 Kotlin 模式、DatResult、會話與能力慣例

npx skills add https://github.com/facebook/meta-wearables-dat-android --skill dat-conventions

DAT SDK Conventions (Android)

Quick Reference

Task	Command
Build app	`./gradlew assembleDebug`
Run tests	`./gradlew test`
Install app	`./gradlew installDebug`
Lint app	`./gradlew lint`

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

Type	Purpose	Example
`DeviceSession`	Device connection lifecycle	`Wearables.createSession(...)`
`Camera`	Camera capability on a session	`session.addCamera(...)`
`Stream`	Video stream from a camera	`camera.stream`
`Display`	Display capability on a session	`session.addDisplay(...)`
`*Selector`	Device targeting	`AutoDeviceSelector`, `SpecificDeviceSelector`
`*Error`	Typed failure surface	`DeviceSessionError`, `StreamError`, `CaptureError`

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