Using the Android for Cars App Library

The Android for Cars App Library allows you to bring your navigation, parking, and charging apps to the car. It does so by providing a set of templates designed to meet driver distraction standards and taking care of details such as the variety of car screen factors and input modalities.

This guide provides an overview of the library’s key features and concepts, and walks you through the process of setting up a simple app.

Before you begin

  1. Review the Android for Cars App Library Design Guidelines.
  2. Review the key terms and concepts listed in this section.
  3. Familiarize yourself with the Android Auto System UI.
  4. Review the Release Notes.
  5. Review the Samples.

Key terms and concepts

Models and Templates
The user interface is represented by a graph of model objects that can be arranged together in different ways as allowed by the template they belong to. Templates are a subset of the models that can act as a root in those graphs. Models include the information to be displayed to the user, in the form of text and images, as well as attributes to configure aspects of the visual appearance of such information (for example, text colors or image sizes). The host converts the models to views that are designed to meet driver distraction standards and takes care of details such as the variety of car screen factors and input modalities.
Host
The host is the back end component that implements the functionality offered by the library’s APIs in order for your app to run in the car. The responsibilities of the host range from discovering your app and managing its lifecycle, to converting your models into views and notifying your app of user interactions. On mobile devices, this host is implemented by Android Auto.
Template restrictions
Different templates enforce restrictions in the content of their models. For example, list templates have limits on the number of items that can be presented to the user. Templates also have restrictions in the way they can be connected to form the flow of a task. For example, the app can only push up to 5 templates to the screen stack. See Template restrictions for more details.
Screen
A Screen is a class provided by the library that apps implement to manage the user interface presented to the user. A Screen has a lifecycle and provides the mechanism for the app to send the template to display when the screen is visible. Screen instances can also be pushed and popped to and from a Screen stack, which ensures they adhere to the template flow restrictions.
CarAppService
A CarAppService is an abstract Service class that your app must implement and export in order to be discovered and managed by the host. Your app's CarAppService is responsible for validating that a host connection can be trusted using CarAppService.createHostValidator, and subsequently providing Session instances for each connection using CarAppService.onCreateSession.
Session

A Session is an abstract class that your app must implement and return using CarAppService.onCreateSession. It serves as the entry point to display information on the car screen, and has a lifecycle that informs the current state of your app on the car screen, such as when your app is visible or hidden.

When a Session is started (such as when the app is first launched), the host requests for the initial Screen to display using the Session.onCreateScreen method.

Install the library

Please follow the Jetpack library release page for instructions on how to add the library to your app.

Configure your app’s manifest files

Before you can create your car app, you need to configure your app’s manifest files.

Declare your CarAppService

The host connects to your app through your CarAppService implementation. You declare this service in your manifest to allow the host to discover and connect to your app.

You also need to declare your app’s category in the category element of your app’s intent filter. See the list of supported app categories for the values allowed for this element.

The following code snippet shows how to declare a car app service for a parking app in your manifest:

<application>
    ...
   <service
       ...
        android:name=".MyCarAppService"
        android:exported="true">
      <intent-filter>
        <action android:name="androidx.car.app.CarAppService"/>
        <category android:name="androidx.car.app.category.PARKING"/>
      </intent-filter>
    </service>

    ...
<application>

Supported App Categories

In order to be listed in the Play Store for Android Auto, the app needs to belong to one of the supported car app categories. You declare your app’s category by adding one or more of the following supported category values in the intent filter when you declare your car app service:

  • androidx.car.app.category.NAVIGATION: An app that provides turn-by-turn navigation directions.
  • androidx.car.app.category.PARKING: An app that provides functionality relevant to finding parking spots.
  • androidx.car.app.category.CHARGING: An app that provides functionality relevant to finding electric vehicle charging stations.

See Android app quality for cars for the detailed description and criteria for apps to belong to each category.

Specify the app name and icon

You need to specify an app name and icon that the host can use to represent your app in the system UI.

You can specify the app name and icon that is used to represent your app using the label and icon elements of your CarAppService:

...
<service
   android:name=".MyCarAppService"
   android:exported="true"
   android:label="@string/my_app_name"
   android:icon="@drawable/my_app_icon">
   ...
</service>
...

If the label or icon are not declared in the service element, the host will fall back to the values specified for the application.

Car App API level

The Car App Library defines its own API levels so that you can know which features of the library are supported by the template host on a given vehicle. To retrieve the highest Car App API Level supported by a host, use the getCarAppApiLevel() method.

You must declare the minimum Car App API Level supported by your app in your AndroidManifest.xml file:

<manifest ...>
    <application ...>
        <meta-data
            android:name="androidx.car.app.minCarApiLevel"
            android:value="1"/>
    </application>
</manifest>

See the documentation for the RequiresCarApi annotation for details on how to maintain backwards compatibility and declare the minimum API level required to use a feature. For a definition of which API Level is required to use a certain feature of the Car App Library, check the reference documentation for CarAppApiLevels.

Create your CarAppService and Session

Your app needs to extend the CarAppService class and implement the CarAppService.onCreateSession method, which returns a Session instance corresponding to the current connection to the host:

Kotlin

class HelloWorldService : CarAppService() {
    ...
    override fun onCreateSession(): Session {
        return HelloWorldSession()
    }
    ...
}

Java

public final class HelloWorldService extends CarAppService {
    ...
    @Override
    @NonNull
    public Session onCreateSession() {
        return new HelloWorldSession();
    }
    ...
}

The Session instance is responsible for returning the Screen instance to use the first time the app is started:

Kotlin

class HelloWorldSession : Session() {
    ...
    override fun onCreateScreen(intent: Intent): Screen {
        return HelloWorldScreen()
    }
    ...
}

Java

public final class HelloWorldSession extends Session {
    ...
    @Override
    @NonNull
    public Screen onCreateScreen(@NonNull Intent intent) {
        return new HelloWorldScreen();
    }
    ...
}

To handle scenarios where your car app needs to start from a screen that is not the home or landing screen of your app (such as handling deep links), you can pre-seed a back stack of screens using ScreenManager.push. before returning from onCreateScreen. Pre-seeding allows users to navigate back to previous screens from the first screen that your app is showing.

Create your start screen

You create the screens displayed by your app by defining classes that extend the Screen class and implementing the Screen.onGetTemplate method, which returns the Template instance representing the state of the UI to display in the car screen.

The following snippet shows how to declare a Screen that uses a PaneTemplate template to display a simple “Hello world!” string:

Kotlin

class HelloWorldScreen(carContext: CarContext) : Screen(carContext) {
    override fun onGetTemplate(): Template {
        val row = Row.Builder().setTitle("Hello world!").build()
        val pane = Pane.Builder().addRow(row).build()
        return PaneTemplate.Builder(pane)
            .setHeaderAction(Action.APP_ICON)
            .build()
    }
}

Java

public class HelloWorldScreen extends Screen {
    @NonNull
    @Override
    public Template onGetTemplate() {
        Row row = new Row.Builder().setTitle("Hello world!").build();
        Pane pane = new Pane.Builder().addRow(row).build();
        return new PaneTemplate.Builder(pane)
            .setHeaderAction(Action.APP_ICON)
            .build();
    }
}

The CarContext class

The CarContext class is a ContextWrapper subclass accessible to your Session and Screen instances, which provides access to car services such as the ScreenManager for managing the screen stack, the AppManager for general app-related functionality such as accessing the Surface object for drawing your navigation app’s map, and the NavigationManager used by turn-by-turn navigation apps to communicate navigation metadata and other navigation-related events with the host. See Access the navigation templates for a comprehensive list of library functionality available to navigation apps.

The CarContext also offers other functionality such as allowing loading drawableresources using the configuration from the car screen, starting an app in the car using intents, and signaling whether your navigation app should display its map in dark mode.

Implement screen navigation

Apps often present a number of different screens, each possibly utilizing different templates, that the user can navigate through as they interact with the interface displayed in the screen.

The ScreenManager class provides a screen stack that you can use to push screens that can be popped automatically when the user selects a back button in the car screen, or uses the hardware back button available in some cars.

The following snippet shows how to add a back action to message template, as well as an action that pushes a new screen when selected by the user:

Kotlin

val template = MessageTemplate.Builder("Hello world!")
    .setHeaderAction(Action.BACK)
    .addAction(
        Action.Builder()
            .setTitle("Next screen")
            .setOnClickListener { screenManager.push(NextScreen(carContext)) }
            .build())
    .build()

Java

MessageTemplate template = new MessageTemplate.Builder("Hello world!")
    .setHeaderAction(Action.BACK)
    .addAction(
        new Action.Builder()
            .setTitle("Next screen")
            .setOnClickListener(
                () -> getScreenManager().push(new NextScreen(getCarContext())))
            .build())
    .build();

The Action.BACK object is a standard Action that automatically invokes ScreenManager.pop. This behavior can be overridden by using the OnBackPressedDispatcher instance available from the CarContext.

To ensure the app is safe while driving, the screen stack can have a maximum depth of 5 screens. See Template restrictions for more details.

Refresh the contents of a template

Your app can request the content of a Screen to be invalidated by calling the Screen.invalidate method. The host subsequently calls back into your app’s Screen.onGetTemplate method to retrieve the template with the new contents.

When refreshing a Screen, it is important to understand the specific content in the template that can be updated so that the host will not count the new template against the template quota. See Template restrictions for more details.

It is recommended that you structure your screens so that there is a one-to-one mapping between a Screen and the type of template it returns through its Screen.onGetTemplate implementation.

Interact with the user

Your app can interact with the user using patterns similar to your mobile app.

Handle user input

Your app can respond to user input by passing the appropriate listeners to the models that support them. The following snippet shows how to create an Action model that sets an OnClickListener that calls back to a method defined by your app’s code:

Kotlin

val action = Action.Builder()
    .setTitle("Navigate")
    .setOnClickListener(::onClickNavigate)
    .build()

Java

Action action = new Action.Builder()
    .setTitle("Navigate")
    .setOnClickListener(this::onClickNavigate)
    .build();

The onClickNavigate method can then start the default navigation car app by using the CarContext.startCarApp method:

Kotlin

private fun onClickNavigate() {
    val intent = Intent(CarContext.ACTION_NAVIGATE, Uri.parse("geo:0,0?q=" + address))
    carContext.startCarApp(intent)
}

Java

private void onClickNavigate() {
    Intent intent = new Intent(CarContext.ACTION_NAVIGATE, Uri.parse("geo:0,0?q=" + address));
    getCarContext().startCarApp(intent);
}

For more details on how to start apps, including the format of the ACTION_NAVIGATE intent, see Start a car app with an intent.

Some actions, such as those that require directing the user to continue the interaction on their mobile devices, are only allowed when the car is parked. You can use the ParkedOnlyOnClickListener to implement those actions. If the car is not parked, the host will display an indication to the user that the action is not allowed in this case. If the car is parked, the code will execute normally. The following snippet shows how to use the ParkedOnlyOnClickListener to open a settings screen on the mobile device:

Kotlin

val row = Row.Builder()
    .setTitle("Open Settings")
    .setOnClickListener(ParkedOnlyOnClickListener.create(::openSettingsOnPhone))
    .build()

Java

Row row = new Row.Builder()
    .setTitle("Open Settings")
    .setOnClickListener(ParkedOnlyOnClickListener.create(this::openSettingsOnPhone))
    .build();

Display notifications

Notifications sent to the mobile device will only show up in the car screen if they are extended with a CarAppExtender. Some notification attributes, such as content title, text, icon, and actions, can be set in the CarAppExtender, overriding the notification's attributes when appearing in the car screen.

The following snippet shows how to send a notification to the car screen that displays a different title than the one shown on the mobile device:

Kotlin

val notification = NotificationCompat.Builder(context, NOTIFICATION_CHANNEL_ID)
    .setContentTitle(titleOnThePhone)
    .extend(
        CarAppExtender.Builder()
            .setContentTitle(titleOnTheCar)
            ...
            .build())
    .build()

Java

Notification notification = new NotificationCompat.Builder(context, NOTIFICATION_CHANNEL_ID)
    .setContentTitle(titleOnThePhone)
    .extend(
        new CarAppExtender.Builder()
            .setContentTitle(titleOnTheCar)
            ...
            .build())
    .build();

Notifications can affect the following parts of the user interface:

  • A heads-up notification (HUN) may be displayed to the user.
  • An entry in the notification center may be added, optionally with a badge visible in the rail.
  • For navigation apps, the notification may be displayed in the rail widget as described in Turn-by-turn notifications.

Applications can choose how to configure their notifications to affect each of those user interface elements by using the notification’s priority, as described in the CarAppExtender documentation.

If NotificationCompat.Builder.setOnlyAlertOnce is called with a value of true, a high-priority notification will display as a HUN only once.

For more information on how to design your car app’s notifications, see Notifications.

Show toasts

Your app can display a toast using CarToast as shown in this snippet:

Kotlin

CarToast.makeText(carContext, "Hello!", CarToast.LENGTH_SHORT).show()

Java

CarToast.makeText(getCarContext(), "Hello!", CarToast.LENGTH_SHORT).show();

Request permissions

If your app needs access to restricted data or actions (for example, getting location access), standard rules of Android permissions apply to your app as well. To request a permission, you can use the CarContext.requestPermissions() method.

On Android Auto, the permissions dialog for the user will appear on the phone. By default, there will be no background behind the dialog. To set a custom background, declare a car app theme in your AndroidManifest.xml file:

<meta-data>
    android:name="androidx.car.app.theme"
    android:resource="@style/MyCarAppTheme />

Then, set the carPermissionActivityLayout attribute for your car app theme:

<resources>
  <style name="MyCarAppTheme">
    <item name="carPermissionActivityLayout">@layout/my_custom_background</item>
  </style>
</resources>

The benefit of using CarContext.requestPermissions() as opposed to using standard Android APIs is that you don't need to launch your own Activity for the sole purpose of creating the permissions dialog. When Android Automotive OS support is available later in the year, you'll also be able to use the same code on both Android Auto and Android Automotive OS rather than having to create platform-dependent flows.

Start a car app with an intent

You can call the CarContext.startCarApp method to perform one of the following actions:

  • Open the dialer to make a phone call.
  • Start turn-by-turn navigation to a location with the default navigation car app.
  • Start your own app with an intent.

The following example shows how to create a notification with an action that opens your app with a screen that shows the details of a parking reservation. You extend the notification instance with a content intent that contains a PendingIntent wrapping an explicit intent to your app’s action:

Kotlin

val notification = notificationBuilder
    ...
    .extend(
        CarAppExtender.Builder()
            .setContentIntent(
                PendingIntent.getBroadcast(
                    context,
                    ACTION_VIEW_PARKING_RESERVATION.hashCode(),
                    Intent(ACTION_VIEW_PARKING_RESERVATION)
                        .setComponent(ComponentName(context, MyNotificationReceiver::class.java)),
                    0))
            .build())

Java

Notification notification = notificationBuilder
    ...
    .extend(
        new CarAppExtender.Builder()
            .setContentIntent(
                PendingIntent.getBroadcast(
                    context,
                    ACTION_VIEW_PARKING_RESERVATION.hashCode(),
                    new Intent(ACTION_VIEW_PARKING_RESERVATION)
                        .setComponent(new ComponentName(context, MyNotificationReceiver.class)),
                    0))
            .build());

Your app must also declare a BroadcastReceiver that is invoked to process the intent when the user selects the action in the notification interface and invokes CarContext.startCarApp with an intent including the data URI:

Kotlin

class MyNotificationReceiver : BroadcastReceiver() {
    override fun onReceive(context: Context, intent: Intent) {
        val intentAction = intent.action
        if (ACTION_VIEW_PARKING_RESERVATION == intentAction) {
            CarContext.startCarApp(
                intent,
                Intent(Intent.ACTION_VIEW)
                    .setComponent(ComponentName(context, MyCarAppService::class.java))
                    .setData(Uri.fromParts(MY_URI_SCHEME, MY_URI_HOST, intentAction)))
        }
    }
}

Java

public class MyNotificationReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        String intentAction = intent.getAction();
        if (ACTION_VIEW_PARKING_RESERVATION.equals(intentAction)) {
            CarContext.startCarApp(
                intent,
                new Intent(Intent.ACTION_VIEW)
                    .setComponent(new ComponentName(context, MyCarAppService.class))
                    .setData(Uri.fromParts(MY_URI_SCHEME, MY_URI_HOST, intentAction)));
        }
    }
}

Finally, the Session.onNewIntent method in your app handles this intent by pushing the parking reservation screen on the stack if not already on top:

Kotlin

override fun onNewIntent(intent: Intent) {
    val screenManager = carContext.getCarService(ScreenManager::class.java)
    val uri = intent.data
    if (uri != null
        && MY_URI_SCHEME == uri.scheme
        && MY_URI_HOST == uri.schemeSpecificPart
        && ACTION_VIEW_PARKING_RESERVATION == uri.fragment
    ) {
        val top = screenManager.top
        if (top !is ParkingReservationScreen) {
            screenManager.push(ParkingReservationScreen(carContext))
        }
    }
}

Java

@Override
public void onNewIntent(@NonNull Intent intent) {
    ScreenManager screenManager = getCarContext().getCarService(ScreenManager.class);
    Uri uri = intent.getData();
    if (uri != null
        && MY_URI_SCHEME.equals(uri.getScheme())
        && MY_URI_HOST.equals(uri.getSchemeSpecificPart())
        && ACTION_VIEW_PARKING_RESERVATION.equals(uri.getFragment())
    ) {
        Screen top = screenManager.getTop();
        if (!(top instanceof ParkingReservationScreen)) {
            screenManager.push(new ParkingReservationScreen(getCarContext()));
        }
    }
}

See Display notifications for more information on how to handle notifications for the car app.

Template restrictions

The host limits the number of templates to display for a given task to a maximum of 5, of which the last template of the 5 must be one of the following types:

  1. NavigationTemplate
  2. PaneTemplate
  3. MessageTemplate

Note that this limit applies to the number of templates, and not the number of Screen instances in the stack. For example, if while in screen A an app sends 2 templates, and then pushes screen B, it can now send 3 more templates. Alternatively, if each screen is structured to send a single template, then the app can push 5 screen instances onto the ScreenManager stack.

There are special cases to these restrictions: template refreshes, back and reset operations.

Template refreshes

Certain content updates are not counted towards the template limit. In general, as long as an app pushes a new template that is of the same type and contains the same main content as the previous template, the new template will not be counted against the quota. For example, updating the toggle state of a row in a ListTemplate does not count against the quota. See the documentation of individual templates to learn more about what types of content updates can be considered a refresh.

Back operations

To enable sub-flows within a task, the host detects when an app is popping a Screen from the ScreenManager stack, and updates the remaining quota based on the number of templates that the app is going backwards by.

For example, if while in screen A, the app sends 2 templates and then pushes screen B and sends 2 more templates, then the app has 1 quota remaining. If the app now pops back to screen A, the host will reset the quota to 3, because the app has gone backwards by 2 templates.

Note that when popping back to a screen, an app must send a template that is of the same type as the one last sent by that screen. Sending any other template types would cause an error. However, as long as the type remains the same during a back operation, an app can freely modify the contents of the template without affecting the quota.

Reset operations

Certain templates have special semantics that signify the end of a task. For example, the NavigationTemplate is a view that is expected to stay on the screen and be refreshed with new turn-by-turn instructions for the user’s consumption. Upon reaching one of these templates, the host will reset the template quota, treating that template as if it is the first step of a new task, thus allowing the app to begin a new task. See the documentation of individual templates to see which ones trigger a reset on the host.

If the host receives an intent to start the app from a notification action or from the launcher, the quota will also be reset. This mechanism allows an app to begin a new task flow from notifications, and it holds true even if an app is already bound and in the foreground.

See Display notifications for more details on how to display your app’s notifications in the car screen, and Start a car app with an intent for how to start your app from a notification action.

Constraints API

Different cars may allow for a different number of Items to be displayed to the user at a time. Use the ConstraintManager to check the content limit at runtime and set the appropriate number of Items in your Templates.

Start by getting a ConstraintManager from the CarContext:

Kotlin

val manager = carContext.getCarService(ConstraintManager::class.java)

Java

ConstraintManager manager = getCarContext().getCarService(ConstraintManager.class);

You can then query the retrieved ConstraintManager object for the relevant content limit. For example, to get the number of items that can be displayed in a grid:

Kotlin

val gridItemLimit = manager.getContentLimit(ConstraintManager.CONTENT_LIMIT_TYPE_GRID)

Java

int gridItemLimit = manager.getContentLimit(ConstraintManager.CONTENT_LIMIT_TYPE_GRID);

Add a sign-in flow

If your app offers a signed-in experience for users, you can use templates such as the SignInTemplate and LongMessageTemplate with Car App API level 2 and above to handle signing in to your app on the car's head unit.

To create a SignInTemplate, you will need to define a SignInMethod. The Car App Library currently supports three sign-in methods:

For example, to implement a template that collects the user's password, start by creating an InputCallback to process and validate user input:

Kotlin

val callback = object : InputCallback {
    override fun onInputSubmitted(text: String) {
        // You will receive this callback when the user presses enter on the keyboard.
    }

    override fun onInputTextChanged(text: String) {
        // You will receive this callback as the user is typing. The update frequency is determined by the host.
    }
}

Java

InputCallback callback = new InputCallback() {
    @Override
    public void onInputSubmitted(@NonNull String text) {
        // You will receive this callback when the user presses enter on the keyboard.
    }

    @Override
    public void onInputTextChanged(@NonNull String text) {
        // You will receive this callback as the user is typing. The update frequency is determined by the host.
    }
};

An InputCallback is required for the InputSignInMethod Builder.

Kotlin

val passwordInput = InputSignInMethod.Builder(callback)
    .setHint("Password")
    .setInputType(InputSignInMethod.INPUT_TYPE_PASSWORD)
    ...
    .build()

Java

InputSignInMethod passwordInput = new InputSignInMethod.Builder(callback)
    .setHint("Password")
    .setInputType(InputSignInMethod.INPUT_TYPE_PASSWORD)
    ...
    .build();

Finally, use your new InputSignInMethod to create a SignInTemplate.

Kotlin

SignInTemplate.Builder(passwordInput)
    .setTitle("Sign in with username and password")
    .setInstructions("Enter your password")
    .setHeaderAction(Action.BACK)
    ...
    .build()

Java

new SignInTemplate.Builder(passwordInput)
    .setTitle("Sign in with username and password")
    .setInstructions("Enter your password")
    .setHeaderAction(Action.BACK)
    ...
    .build();

Add text string variants

Different car screen sizes may show different amounts of text. With Car App API level 2 and above, you can specify multiple variants of a text string to best fit the screen. To see where text variants are accepted, look for templates and components that take a CarText.

You can add text string variants to a CarText with the CarText.Builder.addVariant() method:

Kotlin

val itemTitle = CarText.Builder("This is a very long string")
    .addVariant("Shorter string")
    ...
    .build()

Java

CarText itemTitle = new CarText.Builder("This is a very long string")
    .addVariant("Shorter string")
    ...
    .build();

You can then use this CarText, for example, as the primary text of a GridItem.

Kotlin

GridItem.Builder()
    .addTitle(itemTitle)
    ...
    .build()

Java

new GridItem.Builder()
    .addTitle(itemTitle)
    ...
    build();

Add strings in order from most to least preferred, for example, from longest to shortest. The host will pick the appropriate length string depending on the amount of space available on the car screen.

Car Hardware APIs

Starting with Car App API level 3, the Car App Library introduces APIs that you can use to access vehicle properties and sensors.

Requirements

To use the APIs with Android Auto, start by adding a dependency on androidx.car.app:app-projected to the build.gradle file for your Android Auto module.

Additionally, in your AndroidManifest.xml file, you will need to declare the relevant permissions needed to request the car data you'd like to use. Note that these permissions must also be granted to you by the user.

CarInfo

This table describes the properties surfaced by the CarInfo APIs and the permissions you'll need to request to use them:

Methods Properties Permissions
fetchModel Make, Model, Year
fetchEnergyProfile EV connector types, Fuel types com.google.android.gms.permission.CAR_FUEL
addTollListener
removeTollListener
Toll card state, Toll card type
addEnergyLevelListener
removeEnergyLevelListener
Battery level, Fuel level, Fuel level low, Range remaining com.google.android.gms.permission.CAR_FUEL
addSpeedListener
removeSpeedListener
Raw speed, Display speed (shown on car’s cluster display) com.google.android.gms.permission.CAR_SPEED
addMileageListener
removeMileageListener
Odometer distance com.google.android.gms.permission.CAR_MILEAGE

For example, to get the remaining range, instantiate a CarInfo object, then create and register an OnCarDataAvailableListener:

Kotlin

val carInfo = carContext.getCarService(CarHardwareManager::class.java).carInfo

val listener = OnCarDataAvailableListener<EnergyLevel> { data ->
    if (data.rangeRemainingMeters.status == CarValue.STATUS_SUCCESS) {
      val rangeRemaining = data.rangeRemainingMeters.value
    } else {
      // Handle error
    }
  }

carInfo.addEnergyLevelListener(carContext.mainExecutor, listener)
…
// Unregister the listener when you no longer need updates
carInfo.removeEnergyLevelListener(listener)

Java

CarInfo carInfo = getCarContext().getCarService(CarHardwareManager.class).getCarInfo();

OnCarDataAvailableListener<EnergyLevel> listener = (data) -> {
  if(data.getRangeRemainingMeters().getStatus() == CarValue.STATUS_SUCCESS) {
    float rangeRemaining = data.getRangeRemainingMeters().getValue();
  } else {
    // Handle error
  }
};

carInfo.addEnergyLevelListener(getCarContext().getMainExecutor(), listener);
…
// Unregister the listener when you no longer need updates
carInfo.removeEnergyLevelListener(listener);

You should not assume that the data from the car will be available at all times. If you get an error, check the status of the value you requested to better understand why the data you requested could not be retrieved. Refer to the reference documentation for the full CarInfo class definition.

When Android Automotive OS support is available, you'll also be able to use the same code on both Android Auto and Android Automotive OS rather than having to create platform-dependent flows. However, the permissions needed on Android Automotive OS will be different.

CarSensors

The CarSensors class gives you access to the vehicle's accelerometer, gyroscope, compass, and location data, but note that the availability of these values may depend on the OEM. The format for the data from the accelerometer, gyroscope, and compass is the same as you would get from the SensorManager API. For example, to check the vehicle's heading:

Kotlin

val carSensors = carContext.getCarService(CarHardwareManager::class.java).carSensors

val listener = OnCarDataAvailableListener<Compass> { data ->
    if (data.orientations.status == CarValue.STATUS_SUCCESS) {
      val orientation = data.orientations.value
    } else {
      // Data not available, handle error
    }
  }

carSensors.addCompassListener(CarSensors.UPDATE_RATE_NORMAL, carContext.mainExecutor, listener)
…
// Unregister the listener when you no longer need updates
carSensors.removeCompassListener(listener)

Java

CarSensors carSensors = getCarContext().getCarService(CarHardwareManager.class).getCarSensors();

OnCarDataAvailableListener<Compass> listener = (data) -> {
  if (data.getOrientations().getStatus() == CarValue.STATUS_SUCCESS) {
    List<Float> orientations = data.getOrientations().getValue();
  } else {
    // Data not available, handle error
  }
};

carSensors.addCompassListener(CarSensors.UPDATE_RATE_NORMAL, getCarContext().getMainExecutor(),
    listener);
…
// Unregister the listener when you no longer need updates
carSensors.removeCompassListener(listener);

To access location data from the car, you also need to declare and request the android.permission.ACCESS_FINE_LOCATION permission.

Testing

To test the Car Hardware APIs on Android Auto, you will need version 2.0 rc2 or newer of the Desktop Head Unit (DHU). See Install the DHU for instructions on how to install latest version of the DHU.

The CarAppService, Session and Screen Lifecycles

The Session and Screen classes implement the LifecycleOwner interface. As the user interacts with the app, your Session and Screen objects’ lifecycle callbacks will be invoked, as described in the following diagrams.

The lifecycles of a CarAppService and a Session

Figure 1. The Session lifecycle.

For full details see the documentation of Session.getLifecycle method.

The lifecycle of a Screen

Figure 2. The Screen lifecycle.

For full details see the documentation of Screen.getLifecycle.

Testing Library

The Android for Cars Testing Library provides auxiliary classes that you can use to validate your apps' behavior in a test environment. For example, the SessionController allows you to simulate a connection to the host and verify that the correct Screen and Template are created and returned.

Refer to the Samples for usage examples.

Report an Android for Cars App Library issue

If you find an issue with the library, report it using the Google Issue Tracker. Be sure to fill out all the requested information in the issue template.

Create a new issue

Before filing a new issue, please check if it is listed in the library's release notes or reported in the issues list. You can subscribe and vote for issues by clicking the star for an issue in the tracker. For more information, see Subscribing to an Issue.