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;
}