public MainWindow()
 {
     var factory = new BasicFactory();
     InitializeComponent();
     _repository = factory.GetRepository(RepositoryType.FILEREPOSITORY);
     _calculator = factory.GetCalculator(CalculatorType.HSERATINGCALCULATOR);
     _repository.GradesChanged += RefreshGrid;
     _repository.IOExceptionOccured += IOExceptionAlert;
     dataGridGrades.ItemsSource = _repository.Grades;
 }