Build a navigation app

This page details the different features of the Car App Library that you can use to implement the functionality of your turn-by-turn navigation app.

Declare navigation support in your manifest

Your navigation app needs to declare the androidx.car.app.category.NAVIGATION car app category in the intent filter of its CarAppService:

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

Support navigation intents

To support navigation intents to your app, including those coming from the Google Assistant using a voice query, your app needs to handle the CarContext.ACTION_NAVIGATE intent in its Session.onCreateScreen and Session.onNewIntent.

See the documentation about CarContext.startCarApp for details on the format of the intent.

Access the navigation templates

Navigation apps can access the following templates specifically designed for navigation apps. All these templates display a surface in the background with the map and, during active navigation, turn-by-turn directions.

• NavigationTemplate: also displays an optional informational message and travel estimates during active navigation.
• MapTemplate: presents a compact version of a list (as in the ListTemplate) or of a pane (detailed information with prominent actions, as in the PaneTemplate) next to a map.
• PlaceListNavigationTemplate: also displays a list of places, which can have corresponding markers drawn in the map.
• RoutePreviewNavigationTemplate: also displays a list of routes, one of which can be selected and highlighted in the map.

For more details about how to design your navigation app’s user interface using those templates, see the Android for Cars App Library design guidelines.

To get access to the navigation templates, your app needs to declare the androidx.car.app.NAVIGATION_TEMPLATES permission in its AndroidManifest.xml file:

<uses-permission android:name="androidx.car.app.NAVIGATION_TEMPLATES"/>

Draw the map

Navigation apps can access a Surface to draw the map on relevant templates.

A SurfaceContainer object can then be accessed by setting a SurfaceCallback instance on the AppManager car service:

carContext.getCarService(AppManager::class.java).setSurfaceCallback(surfaceCallback)

carContext.getCarService(AppManager.class).setSurfaceCallback(surfaceCallback);

The SurfaceCallback provides a callback when the SurfaceContainer is available, along with other callbacks when the properties of the Surface change.

To get access to the surface, your app needs to declare the androidx.car.app.ACCESS_SURFACE permission in its AndroidManifest.xml file:

<uses-permission android:name="androidx.car.app.ACCESS_SURFACE"/>

The map’s visible area

The host can draw user interface elements for the templates on top of the map. The host communicates the area that is guaranteed to be unobstructed and fully visible to the user by calling the SurfaceCallback.onVisibleAreaChanged method. Also, to minimize the number of changes, the host calls the SurfaceCallback.onStableAreaChanged method with the smallest rectangle, which is always visible based on the current template.

For example, when a navigation app uses the NavigationTemplate with an action strip on top, the action strip can hide itself when the user has not interacted with the screen for a while to make more space for the map. In this case, there is a callback to onStableAreaChanged and onVisibleAreaChanged with the same rectangle. When the action strip is hidden, only onVisibleAreaChanged is called with the larger area. If the user interacts with the screen, then again only onVisibleAreaChanged is called with the first rectangle.

Support dark mode

Navigation apps must redraw their map onto the Surface instance with the proper dark colors when the host determines conditions warrant it, as described in Android app quality for cars.

To decide whether to draw a dark map, you can use the CarContext.isDarkMode method. Whenever the dark mode status changes, you receive a call to Session.onCarConfigurationChanged.

Communicate navigation metadata

Navigation apps must communicate additional navigation metadata with the host. The host uses the information to provide information to the vehicle head unit and to prevent navigation applications from clashing over shared resources.

Navigation metadata is provided through the NavigationManager car service accessible from the CarContext:

val navigationManager = carContext.getCarService(NavigationManager::class.java)

NavigationManager navigationManager = carContext.getCarService(NavigationManager.class);

Start, end, and stop navigation

For the host to manage multiple navigation apps, routing notifications, and vehicle cluster data, it needs to be aware of the current state of navigation. When a user starts navigation, call NavigationManager.navigationStarted. Similarly, when navigation ends—for example, when the user arrives at their destination or the user cancels navigation—call NavigationManager.navigationEnded.

Only call NavigationManager.navigationEnded when the user finishes navigating. For example, if you need to recalculate the route in the middle of a trip, use Trip.Builder.setLoading(true) instead.

Occasionally, the host needs an app to stop navigation and calls onStopNavigation in a NavigationManagerCallback object provided by your app through NavigationManager.setNavigationManagerCallback. The app must then stop issuing next-turn information in the cluster display, navigation notifications, and voice guidance.

Update trip information

During active navigation, call NavigationManager.updateTrip. The information provided in this call can be used by the vehicle’s cluster and heads-up displays. Depending on the particular vehicle being driven, not all the information is displayed to the user. For example, the Desktop Head Unit (DHU) shows the Step added to the Trip, but does not show the Destination information.

Drawing to the Cluster Display

To provide the most immersive user experience, you may want to go beyond showing basic metadata on the vehicle's cluster display. Starting with Car App API Level 6, navigation apps have the option of rendering their own content directly on the cluster display (in supported vehicles), with the following limitations:

• The cluster display API does not support input controls
• The cluster display should only show map tiles. An active route navigation can optionally be displayed on these tiles.
• The cluster display API only supports use of the NavigationTemplate
  • Unlike main displays, cluster displays may not consistently show all NavigationTemplate UI elements, such as turn-by-turn instructions, ETA cards, and actions. Map tiles are the only consistently displayed UI element.

Declare Cluster Support

To let the host application know that your app supports rendering on cluster displays, you must add an androidx.car.app.category.FEATURE_CLUSTER <category> element to your CarAppService's <intent-filter> as shown in the following snippet:

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

Lifecycle and State Management

Starting with API level 6, the car app lifecycle flow stays the same, but now CarAppService::onCreateSession takes a parameter of type SessionInfo that provides additional information about the Session being created (namely, the display type and the set of supported templates).

Apps have the option to either use the same Session class to handle both the cluster and main display, or create display-specific Sessions to customize behavior on each display (as shown in the following snippet).

override fun onCreateSession(sessionInfo: SessionInfo): Session {
  return if (sessionInfo.displayType == SessionInfo.DISPLAY_TYPE_CLUSTER) {
    ClusterSession()
  } else {
    MainDisplaySession()
  }
}

@Override
@NonNull
public Session onCreateSession(@NonNull SessionInfo sessionInfo) {
  if (sessionInfo.getDisplayType() == SessionInfo.DISPLAY_TYPE_CLUSTER) {
    return new ClusterSession();
  } else {
    return new MainDisplaySession();
  }
}

There are no guarantees about when or if the cluster display is provided, and it's also possible for the cluster Session to be the only Session (for example, the user swapped the main display to another app while your app is actively navigating). The "standard" agreement is that the app gains control of cluster display only after NavigationManager::navigationStarted has been called. However, it's possible for the app to be provided the cluster display while no active navigation is occurring, or to never be provided the cluster display. It is up to your app to handle these scenarios by rendering your app's idle state of map tiles.

The host creates separate binder and CarContext instances per Session. This means that, when using the methods like ScreenManager::push or Screen::invalidate, only the Session from which they are called is affected. Apps should create their own communication channels between these instances if cross-Session communication is needed (for example, by using broadcasts, a shared singleton, or something else).

Testing Cluster Support

You can test your implementation on both Android Auto and Android Automotive OS. For Android Auto, this is done by configuring the Desktop Head Unit to emulate a secondary cluster display. For Android Automotive OS, the generic system images for API level 30 and greater emulate a cluster display.

Customize TravelEstimate with text or an icon

To customize the travel estimate with text, an icon, or both, use the TravelEstimate.Builder class's setTripIcon or setTripText methods. The NavigationTemplate uses TravelEstimate to optionally set text and icons alongside or in place of the estimated time of arrival, remaining time, and remaining distance.

The following snippet uses setTripIcon and setTripText to customize the travel estimate:

TravelEstimate.Builder(Distance.create(...), DateTimeWithZone.create(...))
      ...
      .setTripIcon(CarIcon.Builder(...).build())
      .setTripText(CarText.create(...))
      .build()

new TravelEstimate.Builder(Distance.create(...), DateTimeWithZone.create(...))
      ...
      .setTripIcon(CarIcon.Builder(...).build())
      .setTripText(CarText.create(...))
      .build();

Provide turn-by-turn notifications

Provide turn-by-turn (TBT) navigation instructions using a frequently updated navigation notification. To be treated as a navigation notification in the car screen, your notification's builder must do the following:

1. Mark the notification as ongoing with the NotificationCompat.Builder.setOngoing method.
2. Set the notification’s category to Notification.CATEGORY_NAVIGATION.
3. Extend the notification with a CarAppExtender.

A navigation notification displays in the rail widget at the bottom of the car screen. If the notification's importance level is set to IMPORTANCE_HIGH, it also displays as a heads-up notification (HUN). If the importance is not set with the CarAppExtender.Builder.setImportance method, the notification channel's importance is used.

The app can set a PendingIntent in the CarAppExtender that is sent to the app when the user taps on the HUN or the rail widget.

If NotificationCompat.Builder.setOnlyAlertOnce is called with a value of true, a high-importance notification alerts only once in the HUN.

The following snippet shows how to build a navigation notification:

NotificationCompat.Builder(context, NOTIFICATION_CHANNEL_ID)
    ...
    .setOnlyAlertOnce(true)
    .setOngoing(true)
    .setCategory(NotificationCompat.CATEGORY_NAVIGATION)
    .extend(
        CarAppExtender.Builder()
            .setContentTitle(carScreenTitle)
            ...
            .setContentIntent(
                PendingIntent.getBroadcast(
                    context,
                    ACTION_OPEN_APP.hashCode(),
                    Intent(ACTION_OPEN_APP).setComponent(
                        ComponentName(context, MyNotificationReceiver::class.java)),
                        0))
            .setImportance(NotificationManagerCompat.IMPORTANCE_HIGH)
            .build())
    .build()

new NotificationCompat.Builder(context, NOTIFICATION_CHANNEL_ID)
    ...
    .setOnlyAlertOnce(true)
    .setOngoing(true)
    .setCategory(NotificationCompat.CATEGORY_NAVIGATION)
    .extend(
        new CarAppExtender.Builder()
            .setContentTitle(carScreenTitle)
            ...
            .setContentIntent(
                PendingIntent.getBroadcast(
                    context,
                    ACTION_OPEN_APP.hashCode(),
                    new Intent(ACTION_OPEN_APP).setComponent(
                        new ComponentName(context, MyNotificationReceiver.class)),
                        0))
            .setImportance(NotificationManagerCompat.IMPORTANCE_HIGH)
            .build())
    .build();

Update the TBT notification regularly for distance changes, which updates the rail widget, and only show the notification as a HUN. You can control the HUN behavior by setting the notification's importance with CarAppExtender.Builder.setImportance. Setting the importance to IMPORTANCE_HIGH shows a HUN. Setting it to any other value only updates the rail widget.

Refresh PlaceListNavigationTemplate content

You can let drivers refresh content with the tap of a button while browsing lists of places built with PlaceListNavigationTemplate. To enable list refresh, implement the OnContentRefreshListener interface's onContentRefreshRequested method and use PlaceListNavigationTemplate.Builder.setOnContentRefreshListener to set the listener on the template.

The following snippet shows how to set the listener on the template:

PlaceListNavigationTemplate.Builder()
    ...
    .setOnContentRefreshListener {
        // Execute any desired logic
        ...
        // Then call invalidate() so onGetTemplate() is called again
        invalidate()
    }
    .build()

new PlaceListNavigationTemplate.Builder()
        ...
        .setOnContentRefreshListener(() -> {
            // Execute any desired logic
            ...
            // Then call invalidate() so onGetTemplate() is called again
            invalidate();
        })
        .build();

The refresh button is only shown in the header of the PlaceListNavigationTemplate if the listener has a value.

When the user clicks the refresh button, the onContentRefreshRequested method of your OnContentRefreshListener implementation is called. Within onContentRefreshRequested, call the Screen.invalidate method. The host then calls back into your app’s Screen.onGetTemplate method to retrieve the template with the refreshed content. See Refresh the contents of a template for more information about refreshing templates. As long as the next template returned by onGetTemplate is of the same type, it counts as a refresh and does not count toward the template quota.

Provide audio guidance

To play navigation guidance over the car speakers, your app must request audio focus. As a part of your AudioFocusRequest, set the usage as AudioAttributes.USAGE_ASSISTANCE_NAVIGATION_GUIDANCE. Also, set the focus gain as AudioManager.AUDIOFOCUS_GAIN_TRANSIENT_MAY_DUCK.

Simulate navigation

To verify your app's navigation functionality when you submit it to the Google Play Store, your app must implement the NavigationManagerCallback.onAutoDriveEnabled callback. When this callback is called, your app must simulate navigation to the chosen destination when the user begins navigation. Your app can exit this mode whenever the lifecycle of the current Session reaches the Lifecycle.Event.ON_DESTROY state.

You can test that your implementation of onAutoDriveEnabled is called by executing the following from a command line:

adb shell dumpsys activity service CAR_APP_SERVICE_NAME AUTO_DRIVE

This is shown in the following example:

adb shell dumpsys activity service androidx.car.app.samples.navigation.car.NavigationCarAppService AUTO_DRIVE

Default navigation car app

In Android Auto, the default navigation car app corresponds to the last navigation app that the user launched. The default app receives navigation intents when the user invokes navigation commands through the Assistant or when another app sends an intent to start navigation.

Let users interact with your map

You can add support for users to interact with maps, such as letting them see different parts of a map by zooming and panning. Each template has a different minimum Car App API level requirement. See the following table for the minimum level for the template that you want to implement.

SurfaceCallback methods

The SurfaceCallback interface has several callback methods that let you add interactivity to maps built with the NavigationTemplate, PlaceListNavigationTemplate, RoutePreviewNavigationTemplate, or MapTemplate templates: onClick, onScroll, onScale, and onFling. See the following table for how these callbacks relate to user interactions.

Map action strip

The NavigationTemplate, PlaceListNavigationTemplate, RoutePreviewNavigationTemplate, and MapTemplate templates can have a map action strip for map-related actions such as zooming in and out, recentering, displaying a compass, and other actions you choose to display. The map action strip can have up to four icon-only buttons that can be refreshed without impacting task depth. It hides during idle state and reappears on active state.

To receive map interactivity callbacks, you must add an Action.PAN button in the map action strip. When the user presses the pan button, the host enters pan mode, as described in the following section.

If your app omits the Action.PAN button in the map action strip, it doesn't receive user input from the SurfaceCallback methods, and the host exits any previously activated pan mode.

On a touchscreen, the pan button is not displayed.

Pan mode

In pan mode, the template host translates user input from non-touch input devices, such as rotary controllers and touchpads, into the appropriate SurfaceCallback methods. Respond to the user action to enter or exit pan mode with the setPanModeListener method in the NavigationTemplate.Builder. The host can hide other UI components in the template while the user is in pan mode.

Stable area

The stable area is updated between idle and active states. Determine whether to draw driving-related information, such as speed, speed limit, or road warnings, based on the size of the stable area, so important information on the map doesn’t get obstructed by the map action strip.

Display in-context navigation alerts

Alert displays important information to the driver with optional actions‐without leaving the context of the navigation screen. To provide the best experience to the driver, Alert works within the NavigationTemplate to avoid blocking the navigation route and to minimize driver distraction.

Alert is only available within the NavigationTemplate. To notify the user outside of the NavigationTemplate, consider using a heads-up notification (HUN), as explained in Display notifications.

For example, use Alert to:

• Inform the driver of an update relevant to the current navigation, such as a change in traffic conditions.
• Ask the driver for an update related to the current navigation, such as the existence of a speed trap.
• Propose an upcoming task and ask whether the driver accepts it, such as whether the driver is willing to pick up someone on their way.

In its basic form, an Alert consists of a title and the Alert duration time. The duration time is represented by a progress bar. Optionally, you can add a subtitle, an icon, and up to two Action objects.

Once an Alert is shown, it does not carry over to another template if the driver interaction results in leaving the NavigationTemplate. It stays in the original NavigationTemplate until Alert times out, the user takes an action, or the app dismisses the Alert.

Create an alert

Use Alert.Builder to create an Alert instance:

Alert.Builder(
        /*alertId*/ 1,
        /*title*/ CarText.create("Hello"),
        /*durationMillis*/ 5000
    )
    // The fields below are optional
    .addAction(firstAction)
    .addAction(secondAction)
    .setSubtitle(CarText.create(...))
    .setIcon(CarIcon.APP_ICON)
    .setCallback(...)
    .build()

new Alert.Builder(
        /*alertId*/ 1,
        /*title*/ CarText.create("Hello"),
        /*durationMillis*/ 5000
    )
    // The fields below are optional
    .addAction(firstAction)
    .addAction(secondAction)
    .setSubtitle(CarText.create(...))
    .setIcon(CarIcon.APP_ICON)
    .setCallback(...)
    .build();

If you want to listen for Alert cancellation or dismissal, create an implementation of the AlertCallback interface. The AlertCallback call paths are:

• If the Alert times out, the host calls the AlertCallback.onCancel method with the AlertCallback.REASON_TIMEOUT value. It then calls the AlertCallback.onDismiss method.

• If the driver clicks one of the action buttons, the host calls Action.OnClickListener and then calls AlertCallback.onDismiss.

• If the Alert is not supported, the host calls AlertCallback.onCancel with the AlertCallback.REASON_NOT_SUPPORTED value. The host does not call AlertCallback.onDismiss, because the Alert was not shown.

Configure alert duration

Choose an Alert duration that matches your app’s needs. The recommended duration for a navigation Alert is 10 seconds. Refer to the Android for Cars App Library design guidelines for more information.

Show an alert

To show an Alert, call the AppManager.showAlert method available through your app’s CarContext.

// Show an alert
carContext.getCarService(AppManager.class).showAlert(alert)

• Calling showAlert with an Alert that has an alertId that is the same as the ID of the Alert currently on display does nothing. The Alert doesn’t update. To update an Alert, you must recreate it with a new alertId.
• Calling showAlert with an Alert that has a different alertId than the Alert currently on display dismisses the Alert currently displayed.

Dismiss an alert

While an Alert automatically dismiss due to timeout or driver interaction, you can also manually dismiss an Alert, such as if its information becomes outdated. To dismiss an Alert, call the dismissAlert method with the alertId of the Alert.

// Dismiss the same alert
carContext.getCarService(AppManager.class).dismissAlert(alert.getId())

Calling dismissAlert with an alertId that doesn't match the currently displayed Alert does nothing. It doesn't throw an exception.