public void addScanningCallback(OneSheeldScanningCallback scanningCallback){
  if (scanningCallback != null && !scanningCallbacks.contains(scanningCallback))   scanningCallbacks.add(scanningCallback);
}

public void addScanningCallback ( OneSheeldScanningCallback scanningCallback ) { if ( scanningCallback != null && ! scanningCallbacks . contains ( scanningCallback ) ) scanningCallbacks . add ( scanningCallback ) ; }
add a scanning callback .
