public AudioBookBuilderViewModel() { OuputFileItem = new OuputFileItem(); _audioConverter = new AudioConverter(); _audioConverter.OnConvert += _audioConverter_OnConvert; FileItems = new ObservableCollection <InputFileItem>(); ConvertCommand = new RelayCommand <ObservableCollection <InputFileItem> >(o => _audioConverter.Convert(o), o => !IsBusy && o?.Any() == true); AbortCommand = new RelayCommand <object>(o => _audioConverter.Abort(), o => IsBusy); }