public PreviewImageViewModelWrapper(Task<IEnumerable<Tuple<string, string>>> imagesTask, ISystemServices systemServices)
{
_imageSources = new Dictionary<int, Windows.UI.Xaml.Media.ImageSource>();
_systemServices = systemServices;
IsLoading = true;
imagesTask.ContinueWith(FinishLoad, TaskScheduler.FromCurrentSynchronizationContext());
MoveBack = new RelayCommand(() => CurrentPosition = _currentPosition - 1);
MoveForward = new RelayCommand(() => CurrentPosition = _currentPosition + 1);
}