Projected Hardware

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Applicable XR devices This guidance helps you build experiences for these types of XR devices. Learn about XR device types → Image: untitled Audio &
Display Glasses Learn about XR device types →

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As a user goes through their day, their audio glasses or display glasses might lose their connection to the host device (such as the user's phone) or their glasses might be temporarily unavailable if they take their glasses off. To account for these kinds of changes in device availability, your app can use the XR Device Availability API, which consolidates device availability signals into the standard Android Lifecycle.State values. Use this API to help manage audio routing, hotword activation, and to know when to expect user input based on when the glasses are available.

Understand lifecycle states

The following table lists how device availability signals map to the Lifecycle.State values.

Check and monitor device availability

To check and monitor a device's availability, you'll use a projected context together with the lifecycle state to determine how your app should handle each case:

    // In your phone activity or service, check for projected device connection state before
    // attempting to create a projected device context and get the device lifecycle.
    ProjectedContext.isProjectedDeviceConnected(context, currentCoroutineContext())
        .flatMapLatest { isConnected ->
            if (isConnected) {
                try {
                    // Create the projected device context on connection
                    val projectedContext = ProjectedContext.createProjectedDeviceContext(context)
                    val xrDevice = XrDevice.getCurrentDevice(projectedContext)

                    // Get the device lifecycle
                    xrDevice.getLifecycle().currentStateFlow
                } catch (e: IllegalStateException) {
                    flowOf(Lifecycle.State.DESTROYED)
                }
            } else {
                flowOf(Lifecycle.State.DESTROYED)
            }
        }
        .collect { state ->
            when (state) {
                Lifecycle.State.STARTED -> { /* Device is available (worn) */ }
                Lifecycle.State.CREATED -> { /* Device is unavailable (not worn) */ }
                Lifecycle.State.DESTROYED -> { /* Device is disconnected from host phone */ }
                else -> { /* Handle other states */ }
            }
        }
}

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Key points about the code

• Check for a connection : Before accessing the device lifecycle, call ProjectedContext.isProjectedDeviceConnected to verify that the projected device is connected to the host device.

• Obtain a ProjectedContext : Only call ProjectedContext.createProjectedDeviceContext after verifying the connection, and make sure you pass this context into your XrDevice instance.

• Handle context invalidation : A new deviceId is generated every time a projected device connects. Once the state reaches DESTROYED, the current ProjectedContext is invalid. Stop using it immediately, and wait for a new connection.

• Optimize battery and resources : Gracefully handle app functionality based on the lifecycle state to preserve system resources and reduce battery consumption. For example, you should release glasses-specific resources, such as a camera data stream, when the state transitions from STARTED back to CREATED. The CREATED state indicates the device is no longer being worn, so stopping these processes is essential to prevent unnecessary battery drain and to promote user privacy.