## Set up listeners

After initializing the Driver SDK and creating a `GMTDDeliveryDriverAPI`
instance, you can set up event listeners to monitor the success or failure of
vehicle updates sent to Fleet Engine and your backend. These listeners can
trigger actions within your driver app, such as notifying the driver if
communication with your backend fails.

### Listen for vehicle update events

When the driver enables location updates in the driver app, the Driver SDK sends
regular vehicle updates to Fleet Engine and the customer backend through the
`GMTDDeliveryVehicleReporter` class. You can have the app respond to update
events by setting up the `GMTDVehicleReporterListener` protocol.

With `GMTDVehicleReporterListener`, you can handle the following events:

- `vehicleReporter:didSucceedVehicleUpdate`

  Informs the Driver app that the backend services successfully received the
  vehicle location and state update.
- `vehicleReporter:didFailVehicleUpdate:withError`

  Informs the listener that a vehicle update failed. As long as the driver has
  location updates enabled, the `GMTDDeliveryVehicleReporter` class continues
  to send the latest data to Fleet Engine.

The following example shows how to set up `GMTDVehicleReporterListener` to
handle these events:

### Swift

```swift
import GoogleRidesharingDriver

private let providerID = "INSERT_YOUR_PROVIDER_ID"

class SampleViewController: UIViewController, GMTDVehicleReporterListener {
  private let mapView: GMSMapView

  override func viewDidLoad() {
    // Assumes you have implemented the sample code up to this step.
    deliveryDriverAPI.vehicleReporter.add(self)
  }

  func vehicleReporter(_ vehicleReporter: GMTDDeliveryVehicleReporter, didSucceed vehicleUpdate: GMTDVehicleUpdate) {
    // Handle update succeeded.
  }

  func vehicleReporter(_ vehicleReporter: GMTDDeliveryVehicleReporter, didFail vehicleUpdate: GMTDVehicleUpdate, withError error: Error) {
    // Handle update failed.
  }
}
```

### Objective-C

```objective-c
SampleViewController.h
@interface SampleViewController : UIViewController<GMTDVehicleReporterListener>
@end

SampleViewController.m
#import "SampleViewController.h"
#import "SampleAccessTokenProvider.h"
#import <GoogleRidesharingDriver/GoogleRidesharingDriver.h>

static NSString *const PROVIDER_ID = @"INSERT_YOUR_PROVIDER_ID";

@implementation SampleViewController {
 GMSMapView *_mapView;
}

- (void)viewDidLoad {
  // ASSUMES YOU IMPLEMENTED HAVE THE SAMPLE CODE UP TO THIS STEP.
  [delivervehicleReporter addListener:self];
}

- (void)vehicleReporter:(GMTDDeliveryVehicleReporter *)vehicleReporter didSucceedVehicleUpdate:(GMTDVehicleUpdate *)vehicleUpdate {
  // Handle update succeeded.
}

- (void)vehicleReporter:(GMTDDeliveryVehicleReporter *)vehicleReporter didFailVehicleUpdate:(GMTDVehicleUpdate *)vehicleUpdate withError:(NSError *)error {
  // Handle update failed.
}

@end
```

## Enable location updates

To enable location updates, in the driver app on
`GMTDDeliveryVehicleReporter`, set `locationTrackingEnabled` to
`YES`. Then the
`GMTDDeliveryVehicleReporter` class automatically sends location updates to
Fleet Engine. Additionally, when the `GMSNavigator` is in navigation mode, which
is when a destination is set through `setDestinations`, the
`GMTDDeliveryVehicleReporter` class automatically sends route and ETA updates.

The Driver SDK sets the route to match the driver's current navigation path. To
ensure accurate location updates, set the waypoint in
`-setDestinations:callback:` to match the destination in Fleet Engine.

The following example shows how to enable location updates:

### Swift

```swift
import GoogleRidesharingDriver

private let providerID = "INSERT_YOUR_PROVIDER_ID"

class SampleViewController: UIViewController, GMTDVehicleReporterListener {
  private let mapView: GMSMapView

  override func viewDidLoad() {
    // Assumes you have implemented the sample code up to this step.
    deliveryDriverAPI.vehicleReporter.locationTrackingEnabled = true
  }
}
```

### Objective-C

```objective-c
SampleViewController.m
#import "SampleViewController.h"
#import "SampleAccessTokenProvider.h"
#import <GoogleRidesharingDriver/GoogleRidesharingDriver.h>

static NSString *const PROVIDER_ID = @"INSERT_YOUR_PROVIDER_ID";

@implementation SampleViewController {
 GMSMapView *_mapView;
}

- (void)viewDidLoad {
  // ASSUMES YOU HAVE IMPLEMENTED THE SAMPLE CODE UP TO THIS STEP.
  deliveryDriverAPI.vehicleReporter.locationTrackingEnabled = YES;
}

@end
```

> [!NOTE]
> **Note:** If the device has not moved since the last location update, the `GMSRoadSnappedLocationProvider` class does not send location updates continuously. For example, if a driver is waiting idle in the car. If you want to send a new location update, and have set `GMTDDeliveryVehicleReporter` as a listener after calling `startUpdatingLocation` on `GMSRoadSnappedLocationProvider`, you need to stop and start `GMSRoadSnappedLocationProvider`.

### (Optional) Set the update interval

By default, when you set `locationTrackingEnabled` to `YES`, the Driver SDK
sends location updates to Fleet Engine at a 10-second interval. You can change
the update interval with `locationUpdateInterval` to a minimum update interval
of 5 seconds or a maximum of 60 seconds. More frequent updates may result in
slower requests and errors.