title: Android Studio Ble Gatt connection writing data to a custom service characteristic
body: <p>I am trying to write some custom data to a BLE device with a custom service on it. I have followed this tutorial: <a href="https://www.youtube.com/watch?v=vUbFB1Qypg8&amp;feature=emb_logo" rel="nofollow noreferrer">https://www.youtube.com/watch?v=vUbFB1Qypg8&amp;feature=emb_logo</a> which is from android.</p>
  
  <p>I can see my custom service with data on it. Also via another application (NRF connect) I can write data to this custom service. Therefore, I know its possible to write data to the service.</p>
  
  <p>The issue I have is other examples of how to write data to the custom service use BluetoothGatt whereas, this code seems to use BluetoothLeService instead. This is an issue as the documentation does not seem to have a read API for the BluetoothLeService. So I can not use something like mBluetoothGatt.readCharacteristic(mReadCharacteristic);</p>
  
  <p>How can I go about creating a function to write a value (integer) to the characterisitic.
  My UUID for the service is:  "f3641400-00b0-4240-ba50-05ca45bf8abc"</p>
  
  <p>My UUID for the characteristic is: "f3641401-00b0-4240-ba50-05ca45bf8abc"</p>
  
  <p>For reference my code is below:</p>
  
  <pre><code>public class DeviceControlActivity extends Activity {
  private final static String TAG = 
  DeviceControlActivity.class.getSimpleName();
  
  public static final String EXTRAS_DEVICE_NAME = "DEVICE_NAME";
  public static final String EXTRAS_DEVICE_ADDRESS = "DEVICE_ADDRESS";
  
  private TextView mConnectionState;
  private TextView mDataField;
  private EditText Command_string;
  private BluetoothGatt mGatt;
  private Button btn_gatt_connect;
  private Button btn_live,btn_command;
  private String mDeviceName;
  private String mDeviceAddress;
  private String User_data;
  private ExpandableListView mGattServicesList;
  private BluetoothLeService mBluetoothLeService;
  private ArrayList&lt;ArrayList&lt;BluetoothGattCharacteristic&gt;&gt; mGattCharacteristics =
          new ArrayList&lt;ArrayList&lt;BluetoothGattCharacteristic&gt;&gt;();
  private boolean mConnected = false;
  private BluetoothGattCharacteristic mNotifyCharacteristic;
  
  private final String LIST_NAME = "NAME";
  private final String LIST_UUID = "UUID";
  private String Switch_case ="Connect";
  private boolean Write_ble_command = true;
  
  // Code to manage Service lifecycle.
  private final ServiceConnection mServiceConnection = new ServiceConnection() {
  
      @Override
      public void onServiceConnected(ComponentName componentName, IBinder service) {
          mBluetoothLeService = ((BluetoothLeService.LocalBinder) service).getService();
          if (!mBluetoothLeService.initialize()) {
              Log.e(TAG, "Unable to initialize Bluetooth");
              finish();
          }
          // Automatically connects to the device upon successful start-up initialization.
          mBluetoothLeService.connect(mDeviceAddress);
      }
  
      @Override
      public void onServiceDisconnected(ComponentName componentName) {
          mBluetoothLeService = null;
      }
  };
  
  // Handles various events fired by the Service.
  // ACTION_GATT_CONNECTED: connected to a GATT server.
  // ACTION_GATT_DISCONNECTED: disconnected from a GATT server.
  // ACTION_GATT_SERVICES_DISCOVERED: discovered GATT services.
  // ACTION_DATA_AVAILABLE: received data from the device.  This can be a result of read
  //                        or notification operations.
  private final BroadcastReceiver mGattUpdateReceiver = new BroadcastReceiver() {
      @Override
      public void onReceive(Context context, Intent intent) {
          final String action = intent.getAction();
          if (BluetoothLeService.ACTION_GATT_CONNECTED.equals(action)) {
              mConnected = true;
              updateConnectionState(R.string.connected);
              invalidateOptionsMenu();
          } else if (BluetoothLeService.ACTION_GATT_DISCONNECTED.equals(action)) {
              mConnected = false;
              updateConnectionState(R.string.disconnected);
              invalidateOptionsMenu();
              clearUI();
          } else if (BluetoothLeService.ACTION_GATT_SERVICES_DISCOVERED.equals(action)) {
              // Show all the supported services and characteristics on the user interface.
              displayGattServices(mBluetoothLeService.getSupportedGattServices());
          } else if (BluetoothLeService.ACTION_DATA_AVAILABLE.equals(action)) {
              displayData(intent.getStringExtra(BluetoothLeService.EXTRA_DATA));
          }
      }
  };
  // If a given GATT characteristic is selected, check for supported features.  This sample
  // demonstrates 'Read' and 'Notify' features.  See
  // http://d.android.com/reference/android/bluetooth/BluetoothGatt.html for the complete
  // list of supported characteristic features.
  private final ExpandableListView.OnChildClickListener servicesListClickListner =
          new ExpandableListView.OnChildClickListener() {
              @Override
              public boolean onChildClick(ExpandableListView parent, View v, int groupPosition,
                                          int childPosition, long id) {
                  if (mGattCharacteristics != null) {
                      final BluetoothGattCharacteristic characteristic =
                              mGattCharacteristics.get(groupPosition).get(childPosition);
                      final int charaProp = characteristic.getProperties();
                      if ((charaProp | BluetoothGattCharacteristic.PROPERTY_READ) &gt; 0) {
                          // If there is an active notification on a characteristic, clear
                          // it first so it doesn't update the data field on the user interface.
                          if (mNotifyCharacteristic != null) {
                              mBluetoothLeService.setCharacteristicNotification(
                                      mNotifyCharacteristic, false);
                              mNotifyCharacteristic = null;
                          }
                          mBluetoothLeService.readCharacteristic(characteristic);
                      }
                      if ((charaProp | BluetoothGattCharacteristic.PROPERTY_NOTIFY) &gt; 0) {
                          mNotifyCharacteristic = characteristic;
                          mBluetoothLeService.setCharacteristicNotification(
                                  characteristic, true);
                      }
                      return true;
                  }
                  return false;
              }
          };
  
  private void Gatt_Connect()
  {
      switch(Switch_case) {
          case "Connect":
              btn_gatt_connect.setText("Disconnect");//Presently connected allow to disconnect
              mBluetoothLeService.connect(mDeviceAddress);
              Switch_case = "Disconnect";
              break;
          case "Disconnect":
              btn_gatt_connect.setText("Connect");//Presently disconnected allow to connect
              mBluetoothLeService.disconnect();
              Switch_case = "Connect";
              break;
      }
  
  }
  private void Live_data(){
      //Ensure you are disconnected
      btn_gatt_connect.setText("Connect");//Presently disconnected allow to connect
      mBluetoothLeService.disconnect();//Might only run if connected
      Switch_case = "Connect";
      Intent myIntent = new Intent(DeviceControlActivity.this, MainActivity.class);
      Bundle bundle = new Bundle();
      bundle.putString("User_data", User_data);//Pass through the user's email address to the main activity for display
      myIntent.putExtras(bundle);
      DeviceControlActivity.this.startActivity(myIntent);//Run the main activity}
  }
  private void clearUI() {
      mGattServicesList.setAdapter((SimpleExpandableListAdapter) null);
      mDataField.setText(R.string.no_data);
  }
  @Override
  public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.gatt_services_characteristics);
  
      //Get the extras passed in
      Bundle bundle = getIntent().getExtras();
      mDeviceName = bundle.getString("Device_Name");
      mDeviceAddress = bundle.getString("Device_Address");
      User_data = bundle.getString("User_data");
  
      // Sets up UI references.
      ((TextView) findViewById(R.id.device_address)).setText(mDeviceAddress);
  
      Command_string = (EditText)findViewById(R.id.Command_string);
      btn_gatt_connect = (Button)findViewById(R.id.btn_gatt_connect);
      btn_live = (Button) findViewById(R.id.btn_live);
      btn_command = (Button) findViewById(R.id.btn_command);
      btn_gatt_connect.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View v) {
              Gatt_Connect();
          }
      });
  
      btn_gatt_connect.setText("Disconnect");//Presently disconnected allow to connect
  
      btn_live.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View v) {
              Live_data();
          }
      });
      btn_command.setOnClickListener(new View.OnClickListener() {
          @Override
          public void onClick(View v) {
              Send_Command();//Sends the command in the text box to the nordic board
          }
      });
  
      mGattServicesList = (ExpandableListView) findViewById(R.id.gatt_services_list);
      mGattServicesList.setOnChildClickListener(servicesListClickListner);
      mConnectionState = (TextView) findViewById(R.id.connection_state);
      mDataField = (TextView) findViewById(R.id.data_value);
  
      //setTitle(mDeviceAddress);//Change the title to Scanner as the device is no longer being read
      Intent gattServiceIntent = new Intent(DeviceControlActivity.this, BluetoothLeService.class);
      bindService(gattServiceIntent, mServiceConnection, BIND_AUTO_CREATE);
  }
  @Override
  protected void onResume() {
      super.onResume();
      registerReceiver(mGattUpdateReceiver, makeGattUpdateIntentFilter());
      if (mBluetoothLeService != null) {
          final boolean result = mBluetoothLeService.connect(mDeviceAddress);
          Log.d(TAG, "Connect request result=" + result);
      }
  }
  @Override
  protected void onPause() {
      super.onPause();
      unregisterReceiver(mGattUpdateReceiver);
  }
  @Override
  protected void onDestroy() {
      super.onDestroy();
      unbindService(mServiceConnection);
      mBluetoothLeService = null;
  }
  
  protected void Send_Command()
  {
      Write_ble_command = true;//Write command issued on display gatt service
  }
  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
      getMenuInflater().inflate(R.menu.gatt_services, menu);
      if (mConnected) {
          menu.findItem(R.id.menu_connect).setVisible(false);
          menu.findItem(R.id.menu_disconnect).setVisible(true);
      } else {
          menu.findItem(R.id.menu_connect).setVisible(true);
          menu.findItem(R.id.menu_disconnect).setVisible(false);
      }
      return true;
  }
  @Override
  public boolean onOptionsItemSelected(MenuItem item) {
      switch(item.getItemId()) {
          case R.id.menu_connect:
              mBluetoothLeService.connect(mDeviceAddress);
              return true;
          case R.id.menu_disconnect:
              mBluetoothLeService.disconnect();
              return true;
          case android.R.id.home:
              onBackPressed();
              return true;
      }
      return super.onOptionsItemSelected(item);
  }
  private void updateConnectionState(final int resourceId) {
      runOnUiThread(new Runnable() {
          @Override
          public void run() {
              mConnectionState.setText(resourceId);
          }
      });
  }
  private void displayData(String data) {
      if (data != null) {
          mDataField.setText(data);
      }
  }
  // Demonstrates how to iterate through the supported GATT Services/Characteristics.
  // In this sample, we populate the data structure that is bound to the ExpandableListView
  // on the UI.
  private void displayGattServices(List&lt;BluetoothGattService&gt; gattServices) {
      if (gattServices == null) return;
      String uuid = null;
      String unknownServiceString = getResources().getString(R.string.unknown_service);
      String unknownCharaString = getResources().getString(R.string.unknown_characteristic);
      ArrayList&lt;HashMap&lt;String, String&gt;&gt; gattServiceData = new ArrayList&lt;HashMap&lt;String, String&gt;&gt;();
      ArrayList&lt;ArrayList&lt;HashMap&lt;String, String&gt;&gt;&gt; gattCharacteristicData
              = new ArrayList&lt;ArrayList&lt;HashMap&lt;String, String&gt;&gt;&gt;();
      mGattCharacteristics = new ArrayList&lt;ArrayList&lt;BluetoothGattCharacteristic&gt;&gt;();
  
      // Loops through available GATT Services.
      for (BluetoothGattService gattService : gattServices) {
          HashMap&lt;String, String&gt; currentServiceData = new HashMap&lt;String, String&gt;();
          uuid = gattService.getUuid().toString();
          currentServiceData.put(
                  LIST_NAME, SampleGattAttributes.lookup(uuid, unknownServiceString));
          currentServiceData.put(LIST_UUID, uuid);
          gattServiceData.add(currentServiceData);
  
          ArrayList&lt;HashMap&lt;String, String&gt;&gt; gattCharacteristicGroupData =
                  new ArrayList&lt;HashMap&lt;String, String&gt;&gt;();
          List&lt;BluetoothGattCharacteristic&gt; gattCharacteristics =
                  gattService.getCharacteristics();
          ArrayList&lt;BluetoothGattCharacteristic&gt; charas =
                  new ArrayList&lt;BluetoothGattCharacteristic&gt;();
  
          // Loops through available Characteristics.
          for (BluetoothGattCharacteristic gattCharacteristic : gattCharacteristics) {
              charas.add(gattCharacteristic);
              HashMap&lt;String, String&gt; currentCharaData = new HashMap&lt;String, String&gt;();
              uuid = gattCharacteristic.getUuid().toString();
              currentCharaData.put(
                      LIST_NAME, SampleGattAttributes.lookup(uuid, unknownCharaString));
              currentCharaData.put(LIST_UUID, uuid);
              gattCharacteristicGroupData.add(currentCharaData);
          }
          mGattCharacteristics.add(charas);
          gattCharacteristicData.add(gattCharacteristicGroupData);
      }
  
      SimpleExpandableListAdapter gattServiceAdapter = new SimpleExpandableListAdapter(
              this,
              gattServiceData,
              android.R.layout.simple_expandable_list_item_2,
              new String[] {LIST_NAME, LIST_UUID},
              new int[] { android.R.id.text1, android.R.id.text2 },
              gattCharacteristicData,
              android.R.layout.simple_expandable_list_item_2,
              new String[] {LIST_NAME, LIST_UUID},
              new int[] { android.R.id.text1, android.R.id.text2 }
      );
      mGattServicesList.setAdapter(gattServiceAdapter);
  
  }
  private static IntentFilter makeGattUpdateIntentFilter() {
      final IntentFilter intentFilter = new IntentFilter();
      intentFilter.addAction(BluetoothLeService.ACTION_GATT_CONNECTED);
      intentFilter.addAction(BluetoothLeService.ACTION_GATT_DISCONNECTED);
      intentFilter.addAction(BluetoothLeService.ACTION_GATT_SERVICES_DISCOVERED);
      intentFilter.addAction(BluetoothLeService.ACTION_DATA_AVAILABLE);
      return intentFilter;
  }
  </code></pre>
  
  <p>}</p>