On-demand Rides and Deliveries Solution is currently available only to select partners.

Create and display multi-destination trips

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Multi-destination trips are exclusive trips in which a consumer schedules with a driver that might be making one or more stops before reaching the destination that the consumer originally requested.

The main difference between a multi-destination and a single-destination trip, is that in with a multi-destination trip, the trip operator could make one or more stops in between the origin and dropoff points.

This tutorial walks you through the process of creating a multi-destination trip. It also shows how you can then integrate that trip with your consumer-application so that your customers can visualize the trip progress from their phones. You do this integration using the ConsumerSDK.

Prerequisites

To complete this tutorial, be sure to complete the following:

  1. Set up the Fleet Engine. For more information, see Fleet Engine: Initial setup.

  2. Integrate your app with the Driver SDK. For more information, see Initializing the Driver SDK for Android, and Integration Guide for the Driver SDK for iOS.

  3. Integrate your consumer-facing app with the Consumer SDK. For more information, see Getting Started with the Consumer SDK for Android, and Getting Started with the Consumer SDK for iOS.

  4. Set up authorization tokens. For more information about authorization tokens, see Creating a JSON Web Token for authorization in the Getting Started with Fleet Engine guide, and Authentication and authorization in the Consumer SDK documentation for Fleet Engine.

Step 1. Create a vehicle in Fleet Engine

Vehicles are objects that represent the vehicles in your fleet. You must create them in Fleet Engine in order to be able to track them in the consumer app.

You can create a vehicle using either of the following two approaches:

gRPC
Call the CreateVehicle() method with the CreateVehicleRequest request message. You must have Fleet Engine Super User privileges to call CreateVehicle().
REST
Call https://fleetengine.googleapis.com/v1/providers.vehicles.create.

Caveats

The following caveats apply when you create a vehicle.

  • Be sure to set the initial vehicle state to OFFLINE. This ensures that Fleet Engine can discover your vehicle for trip matching.

  • The vehicle's provider_id must be the same as the project ID of the Google Cloud Project that contains the Service Accounts used for calling Fleet Engine. While multiple service accounts can access the Fleet Engine for the same rideshare provider, Fleet Engine doesn't currently support service accounts from different Google Cloud Projects accessing the same vehicles.

  • The response returned from CreateVehicle() contains the Vehicle instance. The instance is deleted after seven days if it has not been updated using UpdateVehicle(). You should call GetVehicle() before calling CreateVehicle() just to confirm that the vehicle doesn't already exist. If GetVehicle() returns a NOT_FOUND error, then you should proceed with calling CreateVehicle(). For more information, see Vehicles and their lifecycle.

Example

The following provider code sample demonstrates how to create a vehicle in the Fleet Engine.

static final String PROJECT_ID = "my-rideshare-co-gcp-project";

VehicleServiceBlockingStub vehicleService = VehicleService.newBlockingStub(channel);

String parent = "providers/" + PROJECT_ID;

Vehicle vehicle = Vehicle.newBuilder()
    .setVehicleState(VehicleState.OFFLINE)  // Initial state
    .addSupportedTripTypes(TripType.EXCLUSIVE)
    .setMaximumCapacity(4)
    .setVehicleType(VehicleType.newBuilder().setCategory(VehicleType.Category.AUTO))
    .build();

CreateVehicleRequest createVehicleRequest = CreateVehicleRequest.newBuilder()
    .setParent(parent)
    .setVehicleId("8241890")  // Vehicle ID assigned by solution provider.
    .setVehicle(vehicle)      // Initial state.
    .build();

// The Vehicle is created in the OFFLINE state, and no initial position is
// provided.  When the driver app calls the rideshare provider, the state can be
// set to ONLINE, and the driver app updates the vehicle location.
try {
  Vehicle createdVehicle = vehicleService.createVehicle(createVehicleRequest);
} catch (StatusRuntimeException e) {
  Status s = e.getStatus();
  switch (s.getCode()) {
    case ALREADY_EXISTS:
      break;
    case PERMISSION_DENIED:
      break;
  }
  return;
}

To create a Vehicle that supports back-to-back trips, you must set the backToBackEnabled field in the Vehicle object passed to CreateVehicleRequest as true.

Vehicle vehicle = Vehicle.newBuilder()
    .setVehicleState(VehicleState.OFFLINE)
    .addSupportedTripTypes(TripType.EXCLUSIVE)
    .setMaximumCapacity(4)
    .setVehicleType(VehicleType.newBuilder().setCategory(VehicleType.Category.AUTO))
    .setBackToBackEnabled(true) // Set as 'true' so vehicle can be assigned back-to-back trips.
    .build();

Step 2. Enable location tracking

Location tracking refers to tracking the vehicle's location during the trip, where the driver app sends telemetry to the Fleet Engine, which contains the vehicles current location. This constantly updated stream of position information is used to convey the vehicle's progress along the trip's route. When you enable location tracking, the driver app starts sending this telemetry, at a default frequency of once every five seconds.

You enable location tracking for Android and iOS as follows:

Example

The following code example demonstrates how to enable location tracking.

Java

RidesharingVehicleReporter vehicleReporter = ...;

vehicleReporter.enableLocationTracking();

Kotlin

val vehicleReporter = ...

vehicleReporter.enableLocationTracking()

Swift

vehicleReporter.locationTrackingEnabled = true

Objective-C

_vehicleReporter.locationTrackingEnabled = YES;

Step 3. Set the vehicle's state to online

You bring a vehicle into service (that is, to make it available for use) by setting its state to online, but you cannot do this until after you have enabled location tracking.

You set the vehicle's state to online for Android and iOS as follows:

Example

The following code example demonstrates how to set the vehicle's state to ONLINE.

Java

vehicleReporter.setVehicleState(VehicleState.ONLINE);

Kotlin

vehicleReporter.setVehicleState(VehicleState.ONLINE)

Swift

vehicleReporter.update(.online)

Objective-C

[_vehicleReporter updateVehicleState:GMTDVehicleStateOnline];

Step 4. Create a trip in Fleet Engine

To create a multi-destination trip, you must create a Trip object just like you would for single-destination.

A trip is an object that represents a journey, which is a collection geocoordinate points, including origin, waypoints, and dropoff points. You must create one Trip object for each trip request so that the request can be matched to a vehicle and then tracked.

Supply required attributes

The following fields are required to create a multi-destination trip.

parent
A string that includes the provider ID. This must be the same as the project ID of the Google Cloud Project that contains the Service Accounts used for calling Fleet Engine
trip_id
A string that you create, that uniquely identifies this trip.
trip
`Trip` object to create.

You must set the following fields in the Trip object passed to CreateTripRequest:

trip_type
TripType.EXCLUSIVE
pickup_point
The trip's point of origin.
dropoff_point
The trip's dropoff point. This field is not required during trip creation and can be set later by calling `UpdateTrip`.
intermediate_destinations
The list of intermediate destinations that the driver will visit in between pickup and dropoff. Just like dropoff, this field is not required at trip creation and can be set by calling `UpdateTrip`.

Example

The following backend integration sample demonstrates how to create an exclusive multi-destination trip that has a pickup point, a drop-off point, and one intermediate destination.

static final String PROJECT_ID = "my-rideshare-co-gcp-project";
static final String TRIP_ID = "multi-destination-trip-A";

TripServiceBlockingStub tripService = TripService.newBlockingStub(channel);

// Trip initial settings.
String parent = "providers/" + PROJECT_ID;

Trip trip = Trip.newBuilder()
    .setTripType(TripType.EXCLUSIVE)
    .setPickupPoint(
        TerminalLocation.newBuilder().setPoint(
            LatLng.newBuilder()
                .setLatitude(-6.195139).setLongitude(106.820826)))
    .setNumberOfPassengers(1)
    .setDropoffPoint(
        TerminalLocation.newBuilder().setPoint(
            LatLng.newBuilder()
                .setLatitude(-6.1275).setLongitude(106.6537)))
    // Add the list of intermediate destinations.
    .addAllIntermediateDestinations(
        ImmutableList.of(
            TerminalLocation.newBuilder().setPoint(
                LatLng.newBuilder()
                    .setLatitude(-6.195139).setLongitude(106.820826)).build()))
    .build();

// Create the Trip request.
CreateTripRequest createTripRequest = CreateTripRequest.newBuilder()
    .setParent(parent)
    .setTripId(TRIP_ID)  // Trip ID assigned by the Provider server.
    .setTrip(trip)       // Initial state is NEW.
    .build();

// Error handling.
try {
  Trip createdTrip =
      tripService.createTrip(createTripRequest);
} catch (StatusRuntimeException e) {
  Status s = e.getStatus();
  switch (s.getCode()) {
    case ALREADY_EXISTS:  // Trip already exists.
      break;
    case PERMISSION_DENIED:
      break;
  }
  return;
}

Step 5. Update the trip with the vehicle ID and waypoints

You must configure the trip with a vehicle ID so that the Fleet Engine can track the vehicle along its route.

Notes

  • If you don't specify a dropoff or intermediate destinations when you create the trip, you can always do it at this point.

  • If you need to change the vehicle on a trip in progress, then you must set the state of the trip back to new, and then update the trip (as you did above) with the new vehicle ID.

Example

The following backend integration sample demonstrates how to update a trip to add a list of intermediate destinations and set a vehicle ID.

static final String PROJECT_ID = "my-rideshare-co-gcp-project";
static final String TRIP_ID = "multi-destination-trip-A";

String tripName = "providers/" + PROJECT_ID + "/trips/" + TRIP_ID;

TripServiceBlockingStub tripService = TripService.newBlockingStub(channel);

// The trip settings to be updated.
Trip trip = Trip.newBuilder()
    // Add the list of intermediate destinations.
    .addAllIntermediateDestinations(
        ImmutableList.of(
            TerminalLocation.newBuilder().setPoint(
                LatLng.newBuilder()
                    .setLatitude(-6.195139).setLongitude(106.820826)).build()))
    .setVehicleId("8241890")
    .build();

// The trip update request.
UpdateTripRequest updateTripRequest = UpdateTripRequest.newBuilder()
    .setName(tripName)
    .setTrip(trip)
    .setUpdateMask(
        FieldMask.newBuilder()
            .addPaths("intermediate_destinations")
            .addPaths("vehicle_id")
            .build())
    .build();

// Error handling.
try {
  Trip updatedTrip =
      tripService.updateTrip(updateTripRequest);
} catch (StatusRuntimeException e) {
  Status s = e.getStatus();
  switch (s.getCode()) {
    case NOT_FOUND:            // The trip doesn't exist.
      break;
    case PERMISSION_DENIED:
      break;
  }
  return;
}

Step 6. Listen for trip updates in the consumer app

  • For Android, you can listen for data updates from a trip by obtaining a TripModel object from the TripModelManager and registering a TripModelCallback listener.

  • For iOS, you can listen for data updates from a trip by obtaining a GMTCTripModel object from the GMTCTripService and registering a GMTCTripModelSubscriber subscriber.

A TripModelCallback listener and GMTCTripModelSubscriber subscriber let your app receive periodic trip progress updates on each refresh based on the auto refresh interval. Only values that change can trigger the callback. Otherwise, the callback remains silent.

The TripModelCallback.onTripUpdated() and tripModel(_:didUpdate:updatedPropertyFields:) methods are always called, regardless of any data changes.

Example 1

The following code sample demonstrates how to obtain a TripModel from TripModelManager/GMTCTripService and set a listener on it.

Java

// Start journey sharing after a trip has been created via Fleet Engine.
TripModelManager tripModelManager = consumerApi.getTripModelManager();

// Get a TripModel object.
TripModel tripModel = tripModelManager.getTripModel(tripName);

// Register a listener on the trip.
TripModelCallback tripCallback = new TripModelCallback() {
  ...
};
tripModel.registerTripCallback(tripCallback);

// Set the refresh interval.
TripModelOptions tripModelOptions = TripModelOptions.builder()
    .setRefreshInterval(5000) // interval in milliseconds, so 5 seconds
    .build();
tripModel.setTripModelOptions(tripModelOptions);

// The trip stops auto-refreshing when all listeners are unregistered.
tripModel.unregisterTripCallback(tripCallback);

Kotlin

// Start journey sharing after a trip has been created via Fleet Engine.
val tripModelManager = consumerApi.getTripModelManager()

// Get a TripModel object.
val tripModel = tripModelManager.getTripModel(tripName)

// Register a listener on the trip.
val tripCallback = TripModelCallback() {
  ...
}

tripModel.registerTripCallback(tripCallback)

// Set the refresh interval.
val tripModelOptions =
  TripModelOptions.builder()
    .setRefreshInterval(5000) // interval in milliseconds, so 5 seconds
    .build()

tripModel.setTripModelOptions(tripModelOptions)

// The trip stops auto-refreshing when all listeners are unregistered.
tripModel.unregisterTripCallback(tripCallback)

Swift

let tripService = GMTCServices.shared().tripService

// Create a tripModel instance for listening for updates from the trip
// specified by the trip name.
let tripModel = tripService.tripModel(forTripName: tripName)

// Register for the trip update events.
tripModel.register(self)

// Set the refresh interval (in seconds).
tripModel.options.autoRefreshTimeInterval = 5

// Unregister for the trip update events.
tripModel.unregisterSubscriber(self)

Objective-C

GMTCTripService *tripService = [GMTCServices sharedServices].tripService;

// Create a tripModel instance for listening for updates from the trip
// specified by the trip name.
GMTCTripModel *tripModel = [tripService tripModelForTripName:tripName];

// Register for the trip update events.
[tripModel registerSubscriber:self];

// Set the refresh interval (in seconds).
tripModel.options.autoRefreshTimeInterval = 5;

// Unregister for the trip update events.
[tripModel unregisterSubscriber:self];

Example 2

The following code sample demonstrates how to set up a TripModelCallback listener and GMTCTripModelSubscriber subscriber.

Java

// Implements a callback for the trip model so your app can listen for trip
// updates from Fleet Engine.
TripModelCallback subscriber =
  new TripModelCallback() {

    @Override
    public void onTripStatusUpdated(TripInfo tripInfo, @TripStatus int status) {
      // ...
    }

    @Override
    public void onTripActiveRouteUpdated(TripInfo tripInfo, List<LatLng> route) {
      // ...
    }

    @Override
    public void onTripVehicleLocationUpdated(
        TripInfo tripInfo, @Nullable VehicleLocation vehicleLocation) {
      // ...
    }

    @Override
    public void onTripPickupLocationUpdated(
        TripInfo tripInfo, @Nullable TerminalLocation pickup) {
      // ...
    }

    @Override
    public void onTripPickupTimeUpdated(TripInfo tripInfo, @Nullable Long timestampMillis) {
      // ...
    }

    @Override
    public void onTripDropoffLocationUpdated(
        TripInfo tripInfo, @Nullable TerminalLocation dropoff) {
      // ...
    }

    @Override
    public void onTripDropoffTimeUpdated(TripInfo tripInfo, @Nullable Long timestampMillis) {
      // ...
    }

    @Override
    public void onTripETAToNextWaypointUpdated(
        TripInfo tripInfo, @Nullable Long timestampMillis) {
      // ...
    }

    @Override
    public void onTripActiveRouteRemainingDistanceUpdated(
        TripInfo tripInfo, @Nullable Integer distanceMeters) {
      // ...
    }

    @Override
    public void onTripUpdateError(TripInfo tripInfo, TripUpdateError error) {
      // ...
    }

    @Override
    public void onTripUpdated(TripInfo tripInfo) {
      // ...
    }

    @Override
    public void onTripRemainingWaypointsUpdated(
        TripInfo tripInfo, List<TripWaypoint> waypointList) {
      // ...
    }

    @Override
    public void onTripIntermediateDestinationsUpdated(
        TripInfo tripInfo, List<TerminalLocation> intermediateDestinations) {
      // ...
    }

    @Override
    public void onTripRemainingRouteDistanceUpdated(
        TripInfo tripInfo, @Nullable Integer distanceMeters) {
      // ...
    }

    @Override
    public void onTripRemainingRouteUpdated(TripInfo tripInfo, List<LatLng> route) {
      // ...
    }
  };

Kotlin

// Implements a callback for the trip model so your app can listen for trip
// updates from Fleet Engine.
val subscriber =
  object : TripModelCallback() {
    override fun onTripStatusUpdated(tripInfo: TripInfo, status: @TripStatus Int) {
      // ...
    }

    override fun onTripActiveRouteUpdated(tripInfo: TripInfo, route: List<LatLng>) {
      // ...
    }

    override fun onTripVehicleLocationUpdated(
      tripInfo: TripInfo,
      vehicleLocation: VehicleLocation?
    ) {
      // ...
    }

    override fun onTripPickupLocationUpdated(tripInfo: TripInfo, pickup: TerminalLocation?) {
      // ...
    }

    override fun onTripPickupTimeUpdated(tripInfo: TripInfo, timestampMillis: Long?) {
      // ...
    }

    override fun onTripDropoffLocationUpdated(tripInfo: TripInfo, dropoff: TerminalLocation?) {
      // ...
    }

    override fun onTripDropoffTimeUpdated(tripInfo: TripInfo, timestampMillis: Long?) {
      // ...
    }

    override fun onTripETAToNextWaypointUpdated(tripInfo: TripInfo, timestampMillis: Long?) {
      // ...
    }

    override fun onTripActiveRouteRemainingDistanceUpdated(
      tripInfo: TripInfo,
      distanceMeters: Int?
    ) {
      // ...
    }

    override fun onTripUpdateError(tripInfo: TripInfo, error: TripUpdateError) {
      // ...
    }

    override fun onTripUpdated(tripInfo: TripInfo) {
      // ...
    }

    override fun onTripRemainingWaypointsUpdated(
      tripInfo: TripInfo,
      waypointList: List<TripWaypoint>
    ) {
      // ...
    }

    override fun onTripIntermediateDestinationsUpdated(
      tripInfo: TripInfo,
      intermediateDestinations: List<TerminalLocation>
    ) {
      // ...
    }

    override fun onTripRemainingRouteDistanceUpdated(tripInfo: TripInfo, distanceMeters: Int?) {
      // ...
    }

    override fun onTripRemainingRouteUpdated(tripInfo: TripInfo, route: List<LatLng>) {
      // ...
    }
  }

Swift

class TripModelSubscriber: NSObject, GMTCTripModelSubscriber {

  func tripModel(_: GMTCTripModel, didUpdate trip: GMTSTrip?, updatedPropertyFields: GMTSTripPropertyFields) {
    // Update the UI with the new `trip` data.
    updateUI(with: trip)
    ...
  }

  func tripModel(_: GMTCTripModel, didUpdate tripStatus: GMTSTripStatus) {
    // Handle trip status did change.
  }

  func tripModel(_: GMTCTripModel, didUpdateActiveRoute activeRoute: [GMTSLatLng]?) {
    // Handle trip active route did update.
  }

  func tripModel(_: GMTCTripModel, didUpdate vehicleLocation: GMTSVehicleLocation?) {
    // Handle vehicle location did update.
  }

  func tripModel(_: GMTCTripModel, didUpdatePickupLocation pickupLocation: GMTSTerminalLocation?) {
    // Handle pickup location did update.
  }

  func tripModel(_: GMTCTripModel, didUpdateDropoffLocation dropoffLocation: GMTSTerminalLocation?) {
    // Handle drop off location did update.
  }

  func tripModel(_: GMTCTripModel, didUpdatePickupETA pickupETA: TimeInterval) {
    // Handle the pickup ETA did update.
  }

  func tripModel(_: GMTCTripModel, didUpdateDropoffETA dropoffETA: TimeInterval) {
    // Handle the drop off ETA did update.
  }

  func tripModel(_: GMTCTripModel, didUpdateRemaining remainingWaypoints: [GMTSTripWaypoint]?) {
    // Handle updates to the pickup, dropoff or intermediate destinations of the trip.
  }

  func tripModel(_: GMTCTripModel, didFailUpdateTripWithError error: Error?) {
    // Handle the error.
  }

  func tripModel(_: GMTCTripModel, didUpdateIntermediateDestinations intermediateDestinations: [GMTSTerminalLocation]?) {
    // Handle the intermediate destinations being updated.
  }

  ...
}

Objective-C

@interface TripModelSubscriber : NSObject <GMTCTripModelSubscriber>
@end

@implementation TripModelSubscriber

- (void)tripModel:(GMTCTripModel *)tripModel
            didUpdateTrip:(nullable GMTSTrip *)trip
    updatedPropertyFields:(GMTSTripPropertyFields)updatedPropertyFields {
  // Update the UI with the new `trip` data.
  [self updateUIWithTrip:trip];
  ...
}

- (void)tripModel:(GMTCTripModel *)tripModel didUpdateTripStatus:(enum GMTSTripStatus)tripStatus {
  // Handle trip status did change.
}

- (void)tripModel:(GMTCTripModel *)tripModel
    didUpdateActiveRoute:(nullable NSArray<GMTSLatLng *> *)activeRoute {
  // Handle trip route did update.
}

- (void)tripModel:(GMTCTripModel *)tripModel
    didUpdateVehicleLocation:(nullable GMTSVehicleLocation *)vehicleLocation {
  // Handle vehicle location did update.
}

- (void)tripModel:(GMTCTripModel *)tripModel
    didUpdatePickupLocation:(nullable GMTSTerminalLocation *)pickupLocation {
  // Handle pickup location did update.
}

- (void)tripModel:(GMTCTripModel *)tripModel
    didUpdateDropoffLocation:(nullable GMTSTerminalLocation *)dropoffLocation {
  // Handle drop off location did update.
}

- (void)tripModel:(GMTCTripModel *)tripModel didUpdatePickupETA:(NSTimeInterval)pickupETA {
  // Handle the pickup ETA did update.
}

- (void)tripModel:(GMTCTripModel *)tripModel
    didUpdateRemainingWaypoints:(nullable NSArray<GMTSTripWaypoint *> *)remainingWaypoints {
  // Handle updates to the pickup, dropoff or intermediate destinations of the trip.
}

- (void)tripModel:(GMTCTripModel *)tripModel didUpdateDropoffETA:(NSTimeInterval)dropoffETA {
  // Handle the drop off ETA did update.
}

- (void)tripModel:(GMTCTripModel *)tripModel didFailUpdateTripWithError:(nullable NSError *)error {
  // Handle the error.
}

- (void)tripModel:(GMTCTripModel *)tripModel
    didUpdateIntermediateDestinations:
        (nullable NSArray<GMTSTerminalLocation *> *)intermediateDestinations {
  // Handle the intermediate destinations being updated.
}
…
@end

You can access information for the trip any time as follows:

  • Call the Consumer SDK for Android method TripModel.getTripInfo(). Calling this method doesn't force a data refresh, although data still continues to be refreshed at the refresh frequency.

  • Get the Consumer SDK for iOS property GMTCTripModel.currentTrip.

Step 7. Display the journey in the consumer app

You can access the Rides and Deliveries user interface element APIs as follows:

Example

The following code example demonstrates how to start the journey sharing user interface.

Java

JourneySharingSession session = JourneySharingSession.createInstance(tripModel);
consumerController.showSession(session);

Kotlin

val session = JourneySharingSession.createInstance(tripModel)
consumerController.showSession(session)

Swift

let journeySharingSession = GMTCJourneySharingSession(tripModel: tripModel)
mapView.show(journeySharingSession)

Objective-C

GMTCJourneySharingSession *journeySharingSession =
    [[GMTCJourneySharingSession alloc] initWithTripModel:tripModel];
[self.mapView showMapViewSession:journeySharingSession];

By default, the Consumer SDK displays just the active leg in the route, but you have the option of displaying the remaining leg, which includes the intermediate destinations and drop-off.

If you want to display information about waypoints from other trips, you can access all of the waypoints relevant to a trip as follows:

Step 8. Manage the trip state in the Fleet Engine

You specify the state of a trip using one of the TripStatus enumeration values. When a trip's state changes (for example, changing from ENROUTE_TO_PICKUP to ARRIVED_AT_PICKUP) you must update the trip state via the Fleet Engine. Trip state always begins with a value of NEW, and ends with a value of either COMPLETE or CANCELED. For more information, see trip_status.

For a multi-destination trip, in addition to updating the trip state as you would for a single destination trip, you must also update the intermediateDestinationIndex, and provide the intermediateDestinationsVersion in the update request every time you reach an intermediate destination. You must use the following statuses from the TripStatus enumeration.

  • ENROUTE_TO_PICKUP
  • ARRIVED_AT_PICKUP
  • ENROUTE_TO_INTERMEDIATE_DESTINATION
  • ARRIVED_AT_INTERMEDIATE_DESTINATION
  • ENROUTE_TO_DROPOFF
  • COMPLETE

Example

The following backend integration sample demonstrates how to create a multi-destination trip that has passed its pickup point, and is now en route to its first intermediate destination.

static final String PROJECT_ID = "my-rideshare-co-gcp-project";
static final String TRIP_ID = "multi-destination-trip-A";

String tripName = "providers/" + PROJECT_ID + "/trips/" + TRIP_ID;

// Get the trip object from either the Fleet Engine or storage.
Trip trip = …;

TripServiceBlockingStub tripService = TripService.newBlockingStub(channel);

// The trip settings to be updated.
Trip trip = Trip.newBuilder()
    // Trip status cannot return to a previous state once it has passed.
    .setTripStatus(TripStatus.ENROUTE_TO_INTERMEDIATE_DESTINATION)

    // Enroute to the first intermediate destination.
    .setIntermediateDestinationIndex(0)

    // You must provide an intermediate_destinations_version to ensure that you
    // have the same intermediate destinations list as the Fleet Engine.
    .setIntermediateDestinationsVersion(
         trip.getIntermediateDestinationsVersion())
    .build();

// The trip update request.
UpdateTripRequest updateTripRequest = UpdateTripRequest.newBuilder()
    .setName(tripName)
    .setTrip(trip)
    .setUpdateMask(
        FieldMask.newBuilder()
            .addPaths("trip_status")
            .addPaths("intermediate_destination_index")
            // intermediate_destinations_version must not be in the update mask.
            .build())
    .build();

// Error handling.
try {
  Trip updatedTrip =
      tripService.updateTrip(updateTripRequest);
} catch (StatusRuntimeException e) {
  Status s = e.getStatus();
  switch (s.getCode()) {
    case NOT_FOUND:            // The trip doesn't exist.
      break;
    case FAILED_PRECONDITION:  // Either the trip status is invalid, or the
                               // intermediate_destinations_version doesn't
                               // match the Fleet Engine’s.
      break;
    case PERMISSION_DENIED:
      break;
  }
  return;
}