How to display the RSSI of a BLE device continously?

Question

I am trying to implement an android app that scans for BLE devices. Because I need some sort of distance information of the beacons I want to read the RSSI continuously. Currently I am able to display the RSSI but the value does not change. The application reads the value once and does not update the value. I used the sample BLE application from gitHub as a basis.

This is my Bluetooth device:

  class DeviceHolder{
    BluetoothDevice device;
    int rssi;
    public DeviceHolder(BluetoothDevice device, int rssi){
        this. device = device;
        this.rssi = rssi;
    }
}

The list adapter:

 private class LeDeviceListAdapter extends BaseAdapter {
    private ArrayList<BluetoothDevice> mLeDevices;
    private ArrayList<DeviceHolder> mLeHolders;
    private LayoutInflater mInflator;

    public LeDeviceListAdapter() {
        super();
        mLeDevices = new ArrayList<BluetoothDevice>();
        mLeHolders = new ArrayList<DeviceHolder>();
        mInflator = DeviceScanActivity.this.getLayoutInflater();
    }
    public void addDevice(DeviceHolder deviceHolder) {
        if(!mLeDevices.contains(deviceHolder.device)) {
            mLeDevices.add(deviceHolder.device);
            mLeHolders.add(deviceHolder);
        }
    }

and the scan callback:

private BluetoothAdapter.LeScanCallback mLeScanCallback =
        new BluetoothAdapter.LeScanCallback() {

            @Override
            public void onLeScan(final BluetoothDevice device, int rssi, byte[] scanRecord) {
                DeviceHolder deviceHolder = new DeviceHolder(device,rssi);
                runOnUiThread(new DeviceAddTask( deviceHolder ) );
            }
        };

class DeviceAddTask implements Runnable {
    DeviceHolder deviceHolder;

    public DeviceAddTask( DeviceHolder deviceHolder ) {
        this.deviceHolder = deviceHolder;
    }

    public void run() {
        mLeDeviceListAdapter.addDevice(deviceHolder);
        mLeDeviceListAdapter.notifyDataSetChanged();
    }
}

The Bluetooth GattCallback in the BluetoothLeService Activity looks as follows:

private final BluetoothGattCallback mGattCallback = new BluetoothGattCallback() {
    @Override
    public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
        String intentAction;
        if (newState == BluetoothProfile.STATE_CONNECTED) {
            intentAction = ACTION_GATT_CONNECTED;
            mConnectionState = STATE_CONNECTED;
            boolean rssiStatus = mBluetoothGatt.readRemoteRssi();
            broadcastUpdate(intentAction);
            Log.i(TAG, "Connected to GATT server.");
            // Attempts to discover services after successful connection.
            Log.i(TAG, "Attempting to start service discovery:" +
                    mBluetoothGatt.discoverServices());

        } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {
            intentAction = ACTION_GATT_DISCONNECTED;
            mConnectionState = STATE_DISCONNECTED;
            Log.i(TAG, "Disconnected from GATT server.");
            broadcastUpdate(intentAction);
        }
    }

    @Override
    public void onServicesDiscovered(BluetoothGatt gatt, int status) {
        if (status == BluetoothGatt.GATT_SUCCESS) {
            broadcastUpdate(ACTION_GATT_SERVICES_DISCOVERED);
        } else {
            Log.w(TAG, "onServicesDiscovered received: " + status);
        }
    }

    @Override
    public void onCharacteristicRead(BluetoothGatt gatt,
                                     BluetoothGattCharacteristic characteristic,
                                     int status) {
        if (status == BluetoothGatt.GATT_SUCCESS) {
            broadcastUpdate(ACTION_DATA_AVAILABLE, characteristic);
        }
    }

    @Override
    public void onCharacteristicChanged(BluetoothGatt gatt,
                                        BluetoothGattCharacteristic characteristic) {
        broadcastUpdate(ACTION_DATA_AVAILABLE, characteristic);
    }

    public void onReadRemoteRssi(BluetoothGatt gatt,
                                 int rssi, int status){
        super.onReadRemoteRssi(gatt, rssi, status);
        if (status == BluetoothGatt.GATT_SUCCESS) {
            Log.d(TAG, String.format("BluetoothGatt ReadRssi[%d]", rssi));
        } else {
            Log.w(TAG, "onReadRemoteRssi received: " + status);
        }
        broadcastUpdate(ACTION_RSSI_VALUE_READ, rssi);

    }
};

private void broadcastUpdate(final String action) {
    final Intent intent = new Intent(action);
    sendBroadcast(intent);
}

private void broadcastUpdate(final String action, int rssi){
    Log.d(TAG, "broadcastUpdate - rssi");
    final Intent intent = new Intent(action);
    intent.putExtra(DeviceControlActivity.EXTRAS_DEVICE_RSSI, rssi);
    intent.setAction(ACTION_RSSI_VALUE_READ);
    sendBroadcast(intent);
}

I looked up the internet and Stackoverflow for guidance, but the provided solutions did not work for me. I am using a Samsung Galaxy S5 with Android 6.01. Does anyone have a hint how to display the RSSI continuously for non-connected devices (while scanning)? Any hints regarding wrong implementation are welcome too.

Thanks a lot for your help!

Sayus

PS: onReadRemoteRssi is implemented because I want to read the RSSI when the devices are conected as well. This functionality is not important at this time and is only nice to have.

Answer 1

Your application reads an RSSI value once and doesn't update it because when you add a new BluetoothDevice into your adapter, it checks if it already contains one.

    if(!mLeDevices.contains(deviceHolder.device)) {
        mLeDevices.add(deviceHolder.device);
        mLeHolders.add(deviceHolder);
    }

Instead, I would create a Map<BluetoothDevice,Integer> where you update the rssi value for the device: mDeviceRssi.put(device, rssi).