public MainWindowViewModel(IConversionEngine conversionEngine, IUnitsRepository unitsRepository)
        {
            unitsListFrom = new ObservableCollection <Unit>();
            unitsListTo   = new ObservableCollection <Unit>();

            ConvertCommand        = new RelayCommand(o => { var _2 = ConvertNumber(o); }, CanConvertNumber);
            this.conversionEngine = conversionEngine;
            this.unitsRepository  = unitsRepository;
            var _ = LoadList(unitsRepository.InputUnitsCollection(), UnitsListFrom);

            this.PropertyChanged += OnPropertyChanged;
        }