Votre application peut s'abonner aux rattachements de balises Bluetooth à basse consommation (BLE) en utilisant le même mécanisme que celui utilisé pour s'abonner aux messages publiés par d'autres appareils à proximité. Lors de l'abonnement, votre application reçoit automatiquement les messages des balises et des appareils à proximité.
S'abonner aux messages de balise BLE
There are two ways your app can subscribe to BLE beacon messages:
- In the foreground, in response to a user action or event.
- In the background, when your app is not running.
Subscribe in the foreground
When your app subscribes to beacon messages in the foreground, scans are performed continuously until your app unsubscribes. Only start a foreground subscription when your app is active, typically in response to a user action.
Your app can initiate a foreground subscription by calling
Nearby.getMessagesClient(Activity).subscribe(MessageListener, SubscribeOptions)
and setting the Strategy
option to BLE_ONLY
.
The following code snippet demonstrates initiating a foreground subscription
Nearby.getMessagesClient(Activity).subscribe(MessageListener, SubscribeOptions)
:
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
...
mMessageListener = new MessageListener() {
@Override
public void onFound(Message message) {
Log.d(TAG, "Found message: " + new String(message.getContent()));
}
@Override
public void onLost(Message message) {
Log.d(TAG, "Lost sight of message: " + new String(message.getContent()));
}
}
}
// Subscribe to receive messages.
private void subscribe() {
Log.i(TAG, "Subscribing.");
SubscribeOptions options = new SubscribeOptions.Builder()
.setStrategy(Strategy.BLE_ONLY)
.build();
Nearby.getMessagesClient(this).subscribe(mMessageListener, options);
}
When the subscription is no longer required, your app should unsubscribe
by calling
Nearby.getMessagesClient(Activity).unsubscribe(MessageListener)
.
Subscribe in the background
When your app subscribes to beacon messages in the background, low-power scans are triggered at screen-on events, even when your app is not currently active. You can use these scan notifications to "wake up" your app in response to a particular message. Background subscriptions consumes less power than foreground subscriptions, but have higher latency and lower reliability.
Your app can initiate a background subscription by calling
Nearby.getMessagesClient(Activity).subscribe(PendingIntent, SubscribeOptions)
and setting the Strategy
option to BLE_ONLY
.
The following code snippet demonstrates initiating a background subscription by
calling
Nearby.getMessagesClient(Activity).subscribe(PendingIntent, SubscribeOptions)
.
// Subscribe to messages in the background.
private void backgroundSubscribe() {
Log.i(TAG, "Subscribing for background updates.");
SubscribeOptions options = new SubscribeOptions.Builder()
.setStrategy(Strategy.BLE_ONLY)
.build();
Nearby.getMessagesClient(this).subscribe(getPendingIntent(), options);
}
private PendingIntent getPendingIntent() {
return PendingIntent.getBroadcast(this, 0, new Intent(this, BeaconMessageReceiver.class),
PendingIntent.FLAG_UPDATE_CURRENT);
}
The following code snippet demonstrates handling the intent in the
BeaconMessageReceiver
class.
@Override
public void onReceive(Context context, Intent intent) {
Nearby.getMessagesClient(context).handleIntent(intent, new MessageListener() {
@Override
public void onFound(Message message) {
Log.i(TAG, "Found message via PendingIntent: " + message);
}
@Override
public void onLost(Message message) {
Log.i(TAG, "Lost message via PendingIntent: " + message);
}
});
}
When the subscription is no longer required, your app should unsubscribe
by calling
Nearby.getMessagesClient(Activity).unsubscribe(PendingIntent)
.
Parse beacon messages
Beacon attachments are blobs of arbitrary data that you can add to beacons. Each attachment consists of the following parts:
- Namespace: A namespace identifier.
- Type: The data type.
- Data: The data value for the attachment.
The following code snippet demonstrates using a message listener to parse messages received from a BLE beacon:
mMessageListener = new MessageListener() {
@Override
public void onFound(Message message) {
// Do something with the message here.
Log.i(TAG, "Message found: " + message);
Log.i(TAG, "Message string: " + new String(message.getContent()));
Log.i(TAG, "Message namespaced type: " + message.getNamespace() +
"/" + message.getType());
}
...
};
Parsing the content depends on the format of the bytes. This example assumes that the content bytes encode a UTF-8 string, but your beacon message can encode other byte formats (for example a serialized protocol buffer). For more information, see Add Attachments to Beacons.
Pour savoir quels espaces de noms sont associés à votre projet, appelez la méthode namespaces.list.
Remarques :
-
Pour préserver l'autonomie de la batterie, appelez
Nearby.getMessagesClient(Activity).unsubscribe()
dans la fonctiononStop()
de votre activité. Notez que cela ne s'applique que lorsque vous vous abonnez au premier plan. -
Pour réduire la latence, utilisez l'option
Strategy.BLE_ONLY
lorsque vous appelezNearby.getMessagesClient(Activity).subscribe()
. Lorsque cette option est définie, l'API Nearby Messages ne déclenche pas les recherches Bluetooth classiques. Cela réduit la latence pour la détection de balises, car le système n'effectue pas de cycles d'exécution successifs pour tous les types d'analyses possibles. - Pour joindre la charge utile d'un message à une balise, utilisez l'API Proximity Beacon.