public ProjectViewModel(IProjectRepository projectRepository) {
Activities = projectRepository.GetActivities();
ActivitiesCVS = new CollectionViewSource();
var groups = Activities
.OrderBy(i => i.Project)
.GroupBy(i => i.Project)
.Select(g => new { GroupName = g.Key, Items = g });
ActivitiesCVS.Source = groups;
ActivitiesCVS.IsSourceGrouped = true;
ActivitiesCVS.ItemsPath = new PropertyPath("Items");
ActivitiesCollectionView = ActivitiesCVS.View;
}