高级功能

消息类型

默认情况下，订阅会查找与应用的 Google Cloud 控制台项目关联的所有消息。这包括：

• 同一应用在另一设备上发布的消息。
• 相应项目所拥有的附加到 Beacon 的消息。请参阅向 Beacon 添加附件。

您的应用可以使用 MessageFilter 订阅更多类型的附近消息，包括公共信标附件和原始蓝牙低功耗 (BLE) 信标 ID。

公开的 Beacon 附件

开发者可以将信标附件命名空间标记为 PUBLIC。这样一来，所有应用都可以检索这些凭据，无论它们属于哪个 Cloud 控制台项目。如需了解如何公开附件命名空间，请参阅附件可见性。

示例：

// Subscribe for two different public beacon attachment types.
MessageFilter messageFilter = new MessageFilter.Builder()
  .includeNamespacedType(EXAMPLE_PUBLIC_NAMESPACE_A, EXAMPLE_PUBLIC_TYPE_A)
  .includeNamespacedType(EXAMPLE_PUBLIC_NAMESPACE_B, EXAMPLE_PUBLIC_TYPE_B)
  .build();
SubscribeOptions options = new SubscribeOptions.Builder()
  .setStrategy(Strategy.BLE_ONLY)
  .setFilter(messageFilter)
  .build();

MessageListener messageListener = new MessageListener() {
  @Override
  public void onFound(final Message message) {
    // We may want to handle the two types of message differently.
    if (EXAMPLE_PUBLIC_NAMESPACE_A.equals(message.getNamespace())
        && EXAMPLE_PUBLIC_TYPE_A.equals(message.getType())) {
      // Handle a "type A" message.
    } else if (EXAMPLE_PUBLIC_NAMESPACE_B.equals(message.getNamespace())
        && EXAMPLE_PUBLIC_TYPE_B.equals(message.getType())) {
      // Handle a "type B" message.
    }
  }
};

Nearby.getMessagesClient(this).subscribe(messageListener, options);

BLE 信标 ID

您可以使用 Google 的 Beacon 平台将云端中的任意数据附加到 Beacon，从而抽象出在 BLE 数据包中广播的实际 Beacon ID。默认情况下，系统会发现这些附件（请参阅消息类型）。

不过，如果您确实需要发现原始 Beacon ID（例如，为了使用您自己的 Beacon 注册表），则可以这样做。目前支持两种格式：

• Eddystone UID。
  • 您可以使用 MessageFilter.Builder#includeEddystoneUids 查找这些内容。
• iBeacon ID。
  • 您可以使用 MessageFilter.Builder#includeIBeaconIds 查找这些内容。

示例：

// Subscribe for all Eddystone UIDs whose first 10 bytes (the "namespace")
// match MY_EDDYSTONE_UID_NAMESPACE.
//
// Note that the Eddystone UID namespace is separate from the namespace
// field of a Nearby Message.
MessageFilter messageFilter = new MessageFilter.Builder()
  .includeEddystoneUids(MY_EDDYSTONE_UID_NAMESPACE, null /* any instance */)
  .build();
SubscribeOptions options = new SubscribeOptions.Builder()
  .setStrategy(Strategy.BLE_ONLY)
  .setFilter(messageFilter)
  .build();

MessageListener messageListener = new MessageListener() {
  @Override
  public void onFound(final Message message) {
    // Note: Checking the type shown for completeness, but is unnecessary
    // if your message filter only includes a single type.
    if (Message.MESSAGE_NAMESPACE_RESERVED.equals(message.getNamespace())
        && Message.MESSAGE_TYPE_EDDYSTONE_UID.equals(message.getType())) {
      // Nearby provides the EddystoneUid class to parse Eddystone UIDs
      // that have been found nearby.
      EddystoneUid eddystoneUid = EddystoneUid.from(message);
      Log.i(TAG, "Found Eddystone UID: " + eddystoneUid);
    }
  }
};

Nearby.getMessagesClient(this).subscribe(messageListener, options);

RSSI 和距离回调

除了发现和丢失回调之外，当 Nearby 收到与消息关联的 BLE 信号的新信息时，前台订阅还可以更新您的 MessageListener。

注意：

• 目前，这些额外的回调仅针对 BLE Beacon 消息（附件和 Beacon ID）传递。
• 这些额外的回调不会传递给后台 (PendingIntent) 订阅。

示例：

MessageListener messageListener = new MessageListener() {
  /**
   * Called when a message is discovered nearby.
   */
  @Override
  public void onFound(final Message message) {
    Log.i(TAG, "Found message: " + message);
  }

  /**
   * Called when the Bluetooth Low Energy (BLE) signal associated with a message changes.
   *
   * This is currently only called for BLE beacon messages.
   *
   * For example, this is called when we see the first BLE advertisement
   * frame associated with a message; or when we see subsequent frames with
   * significantly different received signal strength indicator (RSSI)
   * readings.
   *
   * For more information, see the MessageListener Javadocs.
   */
  @Override
  public void onBleSignalChanged(final Message message, final BleSignal bleSignal) {
    Log.i(TAG, "Message: " + message + " has new BLE signal information: " + bleSignal);
  }

  /**
   * Called when Nearby's estimate of the distance to a message changes.
   *
   * This is currently only called for BLE beacon messages.
   *
   * For more information, see the MessageListener Javadocs.
   */
  @Override
  public void onDistanceChanged(final Message message, final Distance distance) {
    Log.i(TAG, "Distance changed, message: " + message + ", new distance: " + distance);
  }

  /**
   * Called when a message is no longer detectable nearby.
   */
  @Override
  public void onLost(final Message message) {
    Log.i(TAG, "Lost message: " + message);
  }
};