title: Android bluetooth low energy (ble) writeCharacteristic delay callback
body: <p>I am implementing a application on Android using BLE Api (SDK 18), and I have a issue that the transfer data process is delay very slow. This is my log.</p>
  <blockquote>
  <p>03-12 16:20:05.121: D/BluetoothGatt(13578): writeCharacteristic() - uuid: ...</p>
  <p>03-12 16:20:06.272: D/BluetoothGatt(13578): onCharacteristicWrite() - Device=... UUID=... Status=0</p>
  <p>03-12 16:20:06.972: D/BluetoothGatt(13578): writeCharacteristic() - uuid: ...</p>
  <p>03-12 16:20:08.254: D/BluetoothGatt(13578): onCharacteristicWrite() - Device=... UUID=... Status=0</p>
  <p>03-12 16:20:10.055: D/BluetoothGatt(13578): writeCharacteristic() - uuid: ...</p>
  <p>03-12 16:20:11.257: D/BluetoothGatt(13578): onCharacteristicWrite() - Device=... UUID=... Status=0</p>
  <p>03-12 16:20:12.478: D/BluetoothGatt(13578): writeCharacteristic() - uuid: ...</p>
  <p>03-12 16:20:14.250: D/BluetoothGatt(13578): onCharacteristicWrite() - Device=... UUID=... Status=0</p>
  <p>03-12 16:20:14.960: D/BluetoothGatt(13578): writeCharacteristic() - uuid: ...</p>
  <p>03-12 16:20:16.242: D/BluetoothGatt(13578): onCharacteristicWrite() - Device=... UUID=... Status=0</p>
  <p>03-12 16:20:16.402: D/BluetoothGatt(13578): writeCharacteristic() - uuid: ...</p>
  <p>03-12 16:20:20.225: D/BluetoothGatt(13578): onCharacteristicWrite() - Device=... UUID=... Status=0</p>
  <p>03-12 16:20:20.526: D/BluetoothGatt(13578): writeCharacteristic() - uuid: ...</p>
  <p>03-12 16:20:24.219: D/BluetoothGatt(13578): onCharacteristicWrite() - Device=... UUID=... Status=0</p>
  <p>03-12 16:20:25.360: D/BluetoothGatt(13578): writeCharacteristic() - uuid: ...</p>
  <p>03-12 16:20:27.222: D/BluetoothGatt(13578): onCharacteristicWrite() - Device=... UUID=... Status=0</p>
  </blockquote>
  <p>For more information, I found that every Transfer Progress only completes when it has the onCharacteristicWrite callback, this means that all sending command before receive  onCharacteristicWrite callback will be ignored.</p>
  <p>Is this the flow of Android we have to following or there is any way to setup it skip the callback step to speed up the progress.</p>
  <p>My code is:</p>
  <pre><code>private final BluetoothGattCallback mGattCallback = new BluetoothGattCallback() {
  ......
  @Override
  public void onCharacteristicWrite(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {
      mSending = false;
  }
  };
  
  private void writeCharacteristic() {
      .....
  
      mGattCharacSetIntensity.setValue(data);
      mGattCharacSetIntensity.setWriteType(BluetoothGattCharacteristic.WRITE_TYPE_DEFAULT);
      mBluetoothGatt.writeCharacteristic(mGattCharacSetIntensity);
      return;
  }
  </code></pre>
  <p>EDIT: I have a comparison with iPhone (a BLE transfer data app from AppStore), the BLE transfer data is very quick (less than 0.5 sec), so impressive. How can we work around to SPEED UP the Android BLE Transfer progress?.</p>
  <p>EDIT: If I set WriteType of BluetoothGattCharacteristic to WRITE_TYPE_NO_RESPONSE, and when I send many command sequentially, the Android stores them on a queue and send to remote device one by one after receive writeCharacteristic CallBack, this leads to a issue, when you stop your sending lood, the Android Sending Progress still continue with the delay (Sometime more than 3 sec).</p>