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.

## Before you begin

Make sure you have set up the following things:

- The backend services for your consumer app are in place and your services
  for matching consumers with vehicles is operational.

- You have [set up a map](https://developers.google.com/maps/documentation/mobility/journey-sharing/on-demand/android/create-ui.md.txt) for your app.

## Start following a trip

When your backend server matches a consumer with a vehicle, use
`JourneySharingSession` to start following the trip.

The following sample code demonstrates how to start following a trip after the
view loads.

### Java

```java
public class MainActivity extends AppCompatActivity
    implements ConsumerViewModel.JourneySharingListener  {

  // Class implementation

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Create a TripModel instance to listen for updates to the trip specified by this trip name.
    String tripName = ...;
    TripModelManager tripModelManager = consumerApi.getTripModelManager();
    TripModel tripModel = tripModelManager.getTripModel(tripName);

    // Create a JourneySharingSession instance based on the TripModel.
    JourneySharingSession session = JourneySharingSession.createInstance(tripModel);

    // Add the JourneySharingSession instance on the map for updating the UI.
    consumerController.showSession(session);

    // Register for trip update events.
    tripModel.registerTripCallback(new TripModelCallback() {
      @Override
      public void onTripETAToNextWaypointUpdated(
          TripInfo tripInfo, @Nullable Long timestampMillis) {
        // ...
      }

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

      // ...
    });
  }

  @Override
  protected void onDestroy() {
    super.onDestroy();

    if (journeySharingSession != null) {
      journeySharingSession.stop();
    }
  }
}
```

### Kotlin

```kotlin
class SampleAppActivity : AppCompatActivity(), ConsumerViewModel.JourneySharingListener {

  // Class implementation

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)

    // Create a TripModel instance to listen for updates to the trip specified by this trip name.
    val tripName = "tripName"
    val tripModelManager = consumerApi.getTripModelManager()
    val tripModel = tripModelManager.getTripModel(tripName)

    // Create a JourneySharingSession instance based on the TripModel.
    val session = JourneySharingSession.createInstance(tripModel)

    // Add the JourneySharingSession instance on the map for updating the UI.
    consumerController.showSession(session)

    // Register for trip update events.
    tripModel.registerTripCallback(
      object : TripModelCallback() {
        override fun onTripETAToNextWaypointUpdated(
          tripInfo: TripInfo,
          timestampMillis: Long?,
        ) {
          // ...
        }

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

      // ...
    })
  }

  override fun onDestroy() {
    super.onDestroy()

    journeySharingSession?.stop()
  }
}
```

## Update trip progress

To update trip progress details, such as the distance that the vehicle needs to
travel before arrival and the estimated time of arrival, your app needs to
register and configure a listener as shown in the following examples.

1. Register a listener on a `TripModel` object.

   ### Java

   ```java
   // Create a TripModel instance for listening to updates to the trip specified by this trip name.
   String tripName = ...;
   TripModelManager tripModelManager = consumerApi.getTripModelManager();
   TripModel tripModel = tripModelManager.getTripModel(tripName);

   // Create a JourneySharingSession instance based on the TripModel.
   JourneySharingSession session = JourneySharingSession.createInstance(tripModel);

   // Add the JourneySharingSession instance on the map for updating the UI.
   consumerController.showSession(session);

   // Register for trip update events.
   tripModel.registerTripCallback(new TripModelCallback() {
   @Override
   public void onTripETAToNextWaypointUpdated(
           TripInfo tripInfo, @Nullable Long timestampMillis) {
         // ...
   }

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

   // ...
   });
   ```

   ### Kotlin

   ```kotlin
   // Create a TripModel instance for listening to updates to the trip specified by this trip name.
   val tripName = "tripName"
   val tripModelManager = consumerApi.getTripModelManager()
   val tripModel = tripModelManager.getTripModel(tripName)

   // Create a JourneySharingSession instance based on the TripModel.
   val session = JourneySharingSession.createInstance(tripModel)

   // Add the JourneySharingSession instance on the map for updating the UI.
   consumerController.showSession(session)

   // Register for trip update events.
   tripModel.registerTripCallback(
     object : TripModelCallback() {
       override fun onTripETAToNextWaypointUpdated(
         tripInfo: TripInfo,
         timestampMillis: Long?,
       ) {
         // ...
       }

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

     // ...
   })
   ```
2. Configure the listener for your trip using `TripModelOptions`.

   ### Java

   ```java
   // Set refresh interval to 2 seconds.
   TripModelOptions tripOptions =
         TripModelOptions.builder().setRefreshIntervalMillis(2000).build();
   tripModel.setTripModelOptions(tripOptions);
   ```

   ### Kotlin

   ```kotlin
   // Set refresh interval to 2 seconds.
   val tripOptions = TripModelOptions.builder().setRefreshIntervalMillis(2000).build()
   tripModel.setTripModelOptions(tripOptions)
   ```

### Stop following a trip

Make sure that your app stops following a trip when it is no longer needed, such
as when trip is marked COMPLETE at the backend by the driver. Stopping journey
sharing avoids unnecessary network requests to Fleet Engine and prevents memory
leaks.

Use `JourneySharingSession` to stop following the trip as shown in the
following sample code.

### Java

```java
public class MainActivity extends AppCompatActivity
    implements ConsumerViewModel.JourneySharingListener  {

  // Class implementation

  @Override
  protected void onDestroy() {
    super.onDestroy();

    if (journeySharingSession != null) {
      journeySharingSession.stop();
    }
  }
}
```

### Kotlin

```kotlin
class SampleAppActivity : AppCompatActivity(), ConsumerViewModel.JourneySharingListener {

  // Class implementation

  override fun onDestroy() {
    super.onDestroy()

    journeySharingSession?.stop()
  }
}
```

## Handle trip errors

The `onTripRefreshError` method surfaces errors that occur during trip
monitoring. 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).

### Java

You can extract a gRPC status code that provides details about the error
from the `TripUpdateError` returned from `onTripUpdateError()`.

```java
// Called when there is a trip update error.
@Override
public void onTripUpdateError(TripInfo tripInfo, TripUpdateError error) {
  Status.Code code = error.getStatusCode();
}
```

### Kotlin

You can extract a gRPC status code that provides details about the error
from the `TripUpdateError` returned from `onTripUpdateError()`.

```kotlin
// Called when there is a trip update error.
override fun onTripUpdateError(tripInfo: TripInfo, error: TripUpdateError) {
  val code = error.getStatusCode()
}
```

### 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. |