Select platform: [Android](https://developers.google.com/maps/documentation/mobility/journey-sharing/on-demand/android/share-journey.md.txt "View this page for the Android platform docs.") [iOS](https://developers.google.com/maps/documentation/mobility/journey-sharing/on-demand/ios/share-journey.md.txt "View this page for the iOS platform docs.") [JavaScript](https://developers.google.com/maps/documentation/mobility/journey-sharing/on-demand/javascript/share-journey.md.txt "View this page for the JavaScript platform docs.")

<br />

When you follow a trip, your consumer app displays the location of the
appropriate vehicle to the consumer. To do this, your app needs to start
following a trip, update trip progress, and stop following a trip when it
completes.

This document covers how that process works.

> [!NOTE]
> **Note:** The following procedures assume the backend services are in place and that your services for matching consumers with vehicles is operational.

## Start following a trip

Here's how you start following a trip:

- Gather all user inputs such as drop off and pickup locations
  from a `ViewController`.

- Create a new `ViewController` to start following a trip directly.

The following example shows how to start following a trip immediately after the
view loads.

### Swift

```swift
/*
 * MapViewController.swift
 */
override func viewDidLoad() {
  super.viewDidLoad()
  ...
  self.mapView = GMTCMapView(frame: UIScreen.main.bounds)
  self.mapView.delegate = self
  self.view.addSubview(self.mapView)
}

func mapViewDidInitializeCustomerState(_: GMTCMapView) {
  self.mapView.pickupLocation = self.selectedPickupLocation
  self.mapView.dropoffLocation = self.selectedDropoffLocation

  self.startConsumerMatchWithLocations(
    pickupLocation: self.mapView.pickupLocation!,
    dropoffLocation: self.mapView.dropoffLocation!
  ) { [weak self] (tripName, error) in
    guard let strongSelf = self else { return }
    if error != nil {
      // print error message.
      return
    }
    let tripService = GMTCServices.shared().tripService
    // Create a tripModel instance for listening the update of the trip
    // specified by this trip name.
    let tripModel = tripService.tripModel(forTripName: tripName)
    // Create a journeySharingSession instance based on the tripModel
    let journeySharingSession = GMTCJourneySharingSession(tripModel: tripModel)
    // Add the journeySharingSession instance on the mapView for UI updating.
    strongSelf.mapView.show(journeySharingSession)
    // Register for the trip update events.
    tripModel.register(strongSelf)

    strongSelf.currentTripModel = tripModel
    strongSelf.currentJourneySharingSession = journeySharingSession
    strongSelf.hideLoadingView()
  }

  self.showLoadingView()
}
```

### Objective-C

```objective-c
/*
 * MapViewController.m
 */
- (void)viewDidLoad {
  [super viewDidLoad];
  ...
  self.mapView = [[GMTCMapView alloc] initWithFrame:CGRectZero];
  self.mapView.delegate = self;
  [self.view addSubview:self.mapView];
}

// Handle the callback when the GMTCMapView did initialized.
- (void)mapViewDidInitializeCustomerState:(GMTCMapView *)mapview {
  self.mapView.pickupLocation = self.selectedPickupLocation;
  self.mapView.dropoffLocation = self.selectedDropoffLocation;

  __weak __typeof(self) weakSelf = self;
  [self startTripBookingWithPickupLocation:self.selectedPickupLocation
                           dropoffLocation:self.selectedDropoffLocation
                                completion:^(NSString *tripName, NSError *error) {
                                  __typeof(self) strongSelf = weakSelf;
                                  GMTCTripService *tripService = [GMTCServices sharedServices].tripService;
                                  // Create a tripModel instance for listening to updates to the trip specified by this trip name.
                                  GMTCTripModel *tripModel = [tripService tripModelForTripName:tripName];
                                  // Create a journeySharingSession instance based on the tripModel.
                                  GMTCJourneySharingSession *journeySharingSession =
                                    [[GMTCJourneySharingSession alloc] initWithTripModel:tripModel];
                                  // Add the journeySharingSession instance on the mapView for updating the UI.
                                  [strongSelf.mapView showMapViewSession:journeySharingSession];
                                  // Register for trip update events.
                                  [tripModel registerSubscriber:self];

                                  strongSelf.currentTripModel = tripModel;
                                  strongSelf.currentJourneySharingSession = journeySharingSession;
                                  [strongSelf hideLoadingView];
                                }];
    [self showLoadingView];
}
```

## Stop following a trip

You stop following a trip when it is complete or canceled. The following
example shows how to stop sharing the active trip.

### Swift

```swift
/*
 * MapViewController.swift
 */
func cancelCurrentActiveTrip() {
  // Stop the tripModel
  self.currentTripModel.unregisterSubscriber(self)

  // Remove the journey sharing session from the mapView's UI stack.
  self.mapView.hide(journeySharingSession)
}
```

### Objective-C

```objective-c
/*
 * MapViewController.m
 */
- (void)cancelCurrentActiveTrip {
  // Stop the tripModel
  [self.currentTripModel unregisterSubscriber:self];

  // Remove the journey sharing session from the mapView's UI stack.
  [self.mapView hideMapViewSession:journeySharingSession];
}
```

## Update trip progress

During a trip, you manage trip progress as follows:

- **Start listening for updates** . For an example, see
  [Start listening for updates example](https://developers.google.com/maps/documentation/mobility/journey-sharing/on-demand/ios/share-journey.md.txt#listen-example).

- **Handle any trip updates** . For an example, see
  [Handle trip updates example](https://developers.google.com/maps/documentation/mobility/journey-sharing/on-demand/ios/share-journey.md.txt#handle-updates)

When a trip completes or is canceled, **stop listening for updates** .
For an example, see
[Stop listening for updates example](https://developers.google.com/maps/documentation/mobility/journey-sharing/on-demand/ios/share-journey.md.txt#stop-listen).

### Start listening for updates example

The following example shows how to register the `tripModel` callback.

### Swift

```swift
/*
 * MapViewController.swift
 */
override func viewDidLoad() {
  super.viewDidLoad()
  // Register for trip update events.
  self.currentTripModel.register(self)
}
```

### Objective-C

```objective-c
/*
 * MapViewController.m
 */
- (void)viewDidLoad {
  [super viewDidLoad];
  // Register for trip update events.
  [self.currentTripModel registerSubscriber:self];
  ...
}
```

### Stop listening for updates example

The following example shows how to cancel registration of the `tripModel`
callback.

### Swift

```swift
/*
 * MapViewController.swift
 */
deinit {
  self.currentTripModel.unregisterSubscriber(self)
}
```

### Objective-C

```objective-c
/*
 * MapViewController.m
 */
- (void)dealloc {
  [self.currentTripModel unregisterSubscriber:self];
  ...
}
```

### Handle trip updates example

The following example shows how to implement the `GMTCTripModelSubscriber`
protocol for handling callbacks when the trip state is updated.

### Swift

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

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

func tripModel(_: GMTCTripModel, didUpdateActiveRouteRemainingDistance activeRouteRemainingDistance: Int32) {
  // Handle remaining distance of active route did update.
}

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.
}

func tripModel(_: GMTCTripModel, didUpdateActiveRouteTraffic activeRouteTraffic: GMTSTrafficData?) {
  // Handle trip active route traffic being updated.
}
```

### Objective-C

```objective-c
/*
 * MapViewController.m
 */
#pragma mark - GMTCTripModelSubscriber implementation

- (void)tripModel:(GMTCTripModel *)tripModel
            didUpdateTrip:(nullable GMTSTrip *)trip
    updatedPropertyFields:(enum 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
    didUpdateActiveRouteRemainingDistance:(int32_t)activeRouteRemainingDistance {
   // Handle remaining distance of active route did update.
}

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

- (void)tripModel:(GMTCTripModel *)tripModel
    didUpdateActiveRouteTraffic:(nullable GMTSTrafficData *)activeRouteTraffic {
  // Handle trip active route traffic being updated.
}
```

## Handle trip errors

If you subscribed the `tripModel` and an error occurs, you can get the callback
of `tripModel` by implementing the delegate method
`tripModel(_:didFailUpdateTripWithError:)`. Error
messages follow the Google Cloud Error standard. For detailed error
message definitions and all the error codes, refer to
[Google Cloud Errors documentation](https://cloud.google.com/apis/design/errors).

Here are some common errors that can occur during trip monitoring:

| HTTP | RPC | Description |
|---|---|---|
| 400 | INVALID_ARGUMENT | Client specified an invalid trip name. The trip name must follow the format `providers/{provider_id}/trips/{trip_id}`. The **provider_id** must be the ID of the Cloud Project owned by the service provider. |
| 401 | UNAUTHENTICATED | You receive this error if there are no valid authentication credentials. For example, if the JWT token is signed without a trip ID or the JWT token has expired. |
| 403 | PERMISSION_DENIED | You receive this error if the client does not have sufficient permission (for example, a user with the consumer role tries to call updateTrip), if the JWT token is invalid, or the API is not enabled for the client project. The JWT token might be missing or the token is signed with a trip ID that does not match requested trip ID. |
| 429 | RESOURCE_EXHAUSTED | The resource quota is at zero or the rate of traffic exceeds the limit. |
| 503 | UNAVAILABLE | Service unavailable. Typically the server is down. |
| 504 | DEADLINE_EXCEEDED | Request deadline exceeded. This error only occurs if the caller sets a deadline that is shorter than the method's default deadline (that is, the requested deadline is not enough for the server to process the request) and the request did not finish within the deadline. |

## Handle Consumer SDK Errors

The Consumer SDK sends trip update errors to the consumer app using a callback
mechanism. The callback parameter is a platform-specific return type (
[`TripUpdateError`](https://developers.google.com/maps/documentation/transportation-logistics/on-demand-rides-deliveries-solution/reference/consumer_1/android/reference/com/google/android/libraries/mapsplatform/transportation/consumer/model/TripUpdateError)
on Android, and
[`NSError`](https://developer.apple.com/documentation/foundation/nserror)
on iOS).

### Extract status codes

The errors passed to the callback are typically gRPC errors, and you can also
extract additional information from them in the form of a status code. For the
complete list of status codes, see
[Status codes and their use in gRPC](https://github.com/grpc/grpc/blob/master/doc/statuscodes.md#status-codes-and-their-use-in-grpc).

### Swift

The `NSError` is called back in `tripModel(_:didFailUpdateTripWithError:)`.

```swift
// Called when there is a trip update error.
func tripModel(_ tripModel: GMTCTripModel, didFailUpdateTripWithError error: Error?) {
  // Check to see if the error comes from gRPC.
  if let error = error as NSError?, error.domain == "io.grpc" {
    let gRPCErrorCode = error.code
    ...
  }
}
```

### Objective-C

The `NSError` is called back in `tripModel:didFailUpdateTripWithError:`.

```objective-c
// Called when there is a trip update error.
- (void)tripModel:(GMTCTripModel *)tripModel didFailUpdateTripWithError:(NSError *)error {
  // Check to see if the error comes from gRPC.
  if ([error.domain isEqualToString:@"io.grpc"]) {
    NSInteger gRPCErrorCode = error.code;
    ...
  }
}
```

### Interpret status codes

Status codes cover two kinds of errors: server and network-related errors, and
client-side errors.

#### Server and network errors

The following status codes are for either network or server errors, and you
don't need to any take action to resolve them. The Consumer SDK automatically
recovers from them.

| Status Code | Description |
|---|---|
| ABORTED | The server stopped sending the response. This is normally caused by a server problem. |
| CANCELLED | The server terminated the outgoing response. This normally happens when the app is sent to the background, or when there is a state change in the Consumer app. |
| INTERRUPTED | The server terminated the outgoing response. This normally happens when the app is sent to the background, or when there is a state change in the Consumer app. |
| DEADLINE_EXCEEDED | The server took too long to respond. |
| UNAVAILABLE | The server was unavailable. This is normally caused by a network problem. |

#### Client errors

The following status codes are for client errors, and you must take action to
resolve them. The Consumer SDK continues retrying to refresh the trip until you
end journey sharing, but it won't recover until you take action.

| Status Code | Description |
|---|---|
| INVALID_ARGUMENT | The Consumer app specified an invalid trip name; The trip name must follow the format `providers/{provider_id}/trips/{trip_id}`. |
| NOT_FOUND | The trip was never created. |
| PERMISSION_DENIED | The Consumer app has insufficient permissions. This error occurs when: - The Consumer app doesn't have permissions - The Consumer SDK isn't enabled for the project in the Google Cloud Console. - The JWT token is either missing or is invalid. - The JWT token is signed with a trip ID that doesn't match the requested trip. |
| RESOURCE_EXHAUSTED | The resource quota is at zero, or the rate of traffic flow exceeds the speed limit. |
| UNAUTHENTICATED | The request failed authentication due to an invalid JWT token. This error occurs either when the JWT token is signed without a trip ID, or when the JWT token has expired. |