取得信標訊息

您的應用程式可以使用與訂閱其他鄰近裝置發布訊息相同的機制，訂閱藍牙低功耗 (BLE) 信標附件。訂閱後，應用程式會自動接收來自信標和附近裝置的訊息。

訂閱 BLE 信標訊息

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.

如要找出與專案相關聯的命名空間，請呼叫 namespaces.list。

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