private void UpdateLevels()
 {
     if (SelectedDifficultyLevelScale != null)
     {
         DifficultyLevels.Clear();
         foreach (DifficultyLevel difficultyLevel in _difficultyLevelService.GetAllIn(SelectedDifficultyLevelScale))
         {
             DifficultyLevels.Add(difficultyLevel);
         }
     }
 }
        /// <summary>
        ///     LÄdt die VM relevanten Daten zu einer Schwierigkeitsgradskale
        /// </summary>
        /// <param name="difficultyLevelScale"></param>
        public void LoadData(DifficultyLevelScale difficultyLevelScale)
        {
            if (difficultyLevelScale == null)
            {
                throw new ArgumentNullException(nameof(difficultyLevelScale));
            }
            _difficultyLevelScale = difficultyLevelScale;

            DifficultyLevels.Clear();
            foreach (DifficultyLevel difficultyLevel in _difficultyLevelService.GetAllIn(_difficultyLevelScale))
            {
                IItemWithNameAndScoreViewModel itemViewModel = new ItemWithNameAndScoreViewModel();
                itemViewModel.LoadData(difficultyLevel);
                DifficultyLevels.Add(itemViewModel);
            }
            CommandManager.InvalidateRequerySuggested();
        }