code: private OnValueChangeListener createNumberPickerListener() {
          return new OnValueChangeListener() {
  
              @Override
              public void onValueChange(final android.widget.NumberPicker picker, final int oldValue,
                                        final int newValue) {
                  int value = 0;
  
                  for (int i = 0; i < numberPickers.length; i++) {
                      int exponent = numberPickers.length - i - 1;
                      value += numberPickers[i].getValue() * Math.pow(NUMERIC_SYTEM, exponent);
                  }
  
                  currentNumber = value;
              }
  
          };
      }
docs: Creates and returns a listener, which allows to observe the {@link NumberPicker} widgets,
  which are used by the preference.
  
  @return The listener, which has been created, as an instance of the type {@link
  OnValueChangeListener}