Ran across an interesting new library called Observal that uses a fluent coding model to track items in deep hierarchical object models. The following extension methods are currently provided:

• PropertyChangedExtension, which attaches to the INotifyPropertyChanged.PropertyChanged event
• TraverseExtension, which traverses object hierarchies and adds child property values to the observer
• CollectionExpansionExtension, which adds items in ObservableCollections to the observer
• ItemsChangedExtension, which invokes a callback when items are added or removed

Resulting in code that looks like:

public OrgChartViewModel(IEnumerable<Employee> employees)

{

    _rootEmployees = new ObservableCollection<Employee>(employees);

    var observer = new Observer();

    observer.Extend(new TraverseExtension()).Follow<Employee>(e => e.DirectReports);

    observer.Extend(new CollectionExpansionExtension());

    observer.Extend(new PropertyChangedExtension()).WhenPropertyChanges<Employee>(x => FilterEmployee(x.Source));

    observer.Extend(new ItemsChangedExtension()).WhenAdded<Employee>(FilterEmployee);

    observer.Add(_rootEmployees);

}

I could see some potential for usefulness here…