private void OnSelectedTheoryPartChanged(object sender, RoutedPropertyChangedEventArgs <object> e)
{
_currentModel.ClearSelection();
if (e.NewValue is TestViewModel theoryPart)
{
_currentModel.ShowTest(theoryPart);
}
else if (e.NewValue is DocumentViewModel theoryDoc)
{
_currentModel.ShowDocument(theoryDoc);
}
else if (e.NewValue is PracticeViewModel practiceViewModel)
{
_currentModel.ShowPractice(practiceViewModel);
}
}