Bluetooth Low Energy in Android.

Android provides built-in platform support for Bluetooth Low Energy (BLE) in the central role and provides APIs that apps can use to discover devices, query for services, and transmit information.

Common use cases include the following:

• Transferring small amounts of data between nearby devices.
• Interacting with proximity sensors to give users a customized experience based on their current location.

The following is a summary of key BLE terms and concepts:

         Generic Attribute Profile (GATT)

         Profiles

• Attribute Protocol (ATT)

  Characteristic

  Descriptor

  Service

  
  

  
  

  Find BLE devices

  private BluetoothLeScanner bluetoothLeScanner = bluetoothAdapter.getBluetoothLeScanner();
  private boolean scanning;
  private Handler handler = new Handler();
  
  // Stops scanning after 10 seconds.
  private static final long SCAN_PERIOD = 10000;
  
  private void scanLeDevice() {
      if (!scanning) {
          // Stops scanning after a predefined scan period.
          handler.postDelayed(new Runnable() {
              @Override
              public void run() {
                  scanning = false;
                  bluetoothLeScanner.stopScan(leScanCallback);
              }
          }, SCAN_PERIOD);
  
          scanning = true;
          bluetoothLeScanner.startScan(leScanCallback);
      } else {
          scanning = false;
          bluetoothLeScanner.stopScan(leScanCallback);
      }
  }

  private LeDeviceListAdapter leDeviceListAdapter = new LeDeviceListAdapter();
  
  // Device scan callback.
  private ScanCallback leScanCallback =
          new ScanCallback() {
              @Override
              public void onScanResult(int callbackType, ScanResult result) {
                  super.onScanResult(callbackType, result);
                  leDeviceListAdapter.addDevice(result.getDevice());
                  leDeviceListAdapter.notifyDataSetChanged();
              }
          };

  Connect to a GATT server

  
  

  bluetoothGatt = device.connectGatt(this, false, gattCallback);

  
  

  
  

  Set up a bound service

  
  

  class BluetoothLeService extends Service {
  
      private Binder binder = new LocalBinder();
  
      @Nullable
      @Override
      public IBinder onBind(Intent intent) {
          return binder;
      }
  
      class LocalBinder extends Binder {
          public BluetoothLeService getService() {
              return BluetoothLeService.this;
          }
      }
  }

  class BluetoothLeService extends Service {
  
      public static final String TAG = "BluetoothLeService";
  
      private BluetoothAdapter bluetoothAdapter;
  
      public boolean initialize() {
          bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
          if (bluetoothAdapter == null) {
              Log.e(TAG, "Unable to obtain a BluetoothAdapter.");
              return false;
          }
          return true;
      }
  
      ...
  }

  class DeviceControlsActivity extends AppCompatActivity {
  
      private ServiceConnection serviceConnection = new ServiceConnection() {
          @Override
          public void onServiceConnected(ComponentName name, IBinder service) {
              bluetoothService = ((LocalBinder) service).getService();
              if (bluetoothService != null) {
                  if (!bluetoothService.initialize()) {
                      Log.e(TAG, "Unable to initialize Bluetooth");
                      finish();
                  }
                  // perform device connection
              }
          }
  
          @Override
          public void onServiceDisconnected(ComponentName name) {
              bluetoothService = null;
          }
      };
  
      ...
  }