从Bluetooth Gatt Features获取通知

Question

我目前正在尝试连接此设备Micro:bit。该设备具有多种服务和特性。问题是一旦连接，设备只返回1个服务和0个特征。我错过了什么？

public class MainActivity extends Activity {

    private BluetoothAdapter bleAdapter;
    private BluetoothGattCharacteristic UART;
    private BluetoothGattDescriptor descriptor;
    private TextView connectionState;

    private final UUID SERVICE = UUID.fromString("6E400001-B5A3-F393-E0A9-E50E24DCCA9E");
    private final UUID CHARACTERISTIC = UUID.fromString("6E400003-B5A3-F393-E0A9-E50E24DCCA9E");
    private final UUID CONFIG_DESCRIPTOR = UUID.fromString("00002902-0000-1000-8000-00805f9b34fb");

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Check if the system supports Bluetooth Low Energy
        if (!getPackageManager().hasSystemFeature(PackageManager.FEATURE_BLUETOOTH_LE)) {
            Toast.makeText(this, "BLE Not Supported", Toast.LENGTH_SHORT).show();
            finish();
        }

        // Take the system BLE adapter
        bleAdapter = ((BluetoothManager) getSystemService(BLUETOOTH_SERVICE)).getAdapter();

        // Enable Bluetooth in case it's off.
        if (bleAdapter == null || !bleAdapter.isEnabled()) {
            Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(enableBtIntent, 1);
        }

        // Get paired devices.
        Set<BluetoothDevice> pairedDevices = bleAdapter.getBondedDevices();

        for (BluetoothDevice device : pairedDevices) {

            // Connect to Micro:Bit (the only one paired device)
            device.connectGatt(this, true, new BluetoothGattCallback() {

                // Check if it connects or disconnects from the Micro:Bit
                @Override
                public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
                    super.onConnectionStateChange(gatt, status, newState);

                    switch (newState) {
                        case BluetoothProfile.STATE_CONNECTED:
                            gatt.discoverServices();
                            runOnUiThread(new Runnable() {
                                public void run() {
                                    connectionState = findViewById(R.id.state);
                                    connectionState.setText("Connected = True");
                                    connectionState.setTextColor(Color.GREEN);
                                }
                            });
                            break;

                        case BluetoothProfile.STATE_DISCONNECTED:
                            gatt.disconnect();
                            runOnUiThread(new Runnable() {
                                public void run() {
                                    connectionState = findViewById(R.id.state);
                                    connectionState.setText("Connected = False");
                                    connectionState.setTextColor(Color.RED);
                                }
                            });
                    }
                }

                @Override
                public void onServicesDiscovered(BluetoothGatt gatt, int status) {
                    super.onServicesDiscovered(gatt, status);

                    List<BluetoothGattService> list = new ArrayList<BluetoothGattService>();
                    list = gatt.getServices();

                    for (BluetoothGattService elem : list){
                        Log.i("Service", elem.getUuid().toString());

                        List<BluetoothGattCharacteristic> list2 = new ArrayList<BluetoothGattCharacteristic>();
                        list2 = elem.getCharacteristics();

                        for (BluetoothGattCharacteristic elem2: list2) {
                            Log.i("Characteristic", elem2.getUuid().toString());
                        }
                    }

                    // Try to set notifications 

                    UART = gatt.getService(SERVICE).getCharacteristic(CHARACTERISTIC);
                    gatt.setCharacteristicNotification(UART,true);
                    descriptor = UART.getDescriptor(CONFIG_DESCRIPTOR);
                    descriptor.setValue(BluetoothGattDescriptor.ENABLE_NOTIFICATION_VALUE);
                    gatt.writeDescriptor(descriptor);

                }

                // Activate every time UART Characteristic is updated
                @Override
                public void onCharacteristicChanged(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic) {
                    super.onCharacteristicChanged(gatt, characteristic);

                    runOnUiThread(new Runnable() {
                        public void run() {
                            TextView x = (TextView) findViewById(R.id.x_axis);
                            TextView y = (TextView) findViewById(R.id.y_axis);
                            TextView z = (TextView) findViewById(R.id.z_axis);

                            x.setText("HELLO");
                            y.setText("IT ");
                            z.setText("WORKS!");
                        }
                    });
                }
            });
        }
    }
}

来自变量SERVICE和CHARACTERISTIC的UUID来自here。我尝试连接到该UART服务，并在此设备更新TX特性时收到通知。但我只是从onServicesDiscovered（）获得了一个循环上的服务，如果我尝试gatt.getService（SERVICE）.getCharacteristic（CHARACTERISTIC），我会得到空指针。我做错了什么？