private void stopSensors() {
   Logger.d(this, "stopSensors");
   // Store data.
   saveSessionData();
   // Clear state.
   Preferences.clearStoredValues(this);
   mSessionStartTimeMillis = Integer.MIN_VALUE;
   mSessionInitialSteps = Integer.MIN_VALUE;
   mSensorInfo = null;
   // Sensors.
   unregisterSensors();
   if (mListener != null) {
     mListener.onSensorStop();
   }
 }
 @Override
 public void onDestroy() {
   Logger.d(this, "onDestroy");
   Preferences.clearStoredValues(this);
 }