CollectionView live sorting callback

Question

I have a TreeView that uses a ListCollectionView with a custom IComprarer and live shaping to order its children. When the currently selected TreeViewItem is re-sorted in the view, I'd like the TreeView to automatically scroll to the TreeViewItem's new position. However, I can't find a way to be notified when the ListCollectionView applies a new sort, and the behavior I want doesn't seem to be built into the TreeViewControl.

Is there a way I can be notified when the ListCollectionView recomputes its sort order?

Answer 1

I believe the event CollectionChanged is what you need. You can do something like this:

((ICollectionView)yourListCollectionView).CollectionChanged += handler;

The reason we have to cast here is CollectionChanged is implemented as the member of INotifyPropertyChanged (ICollectionView inherits from this interface), source code here:

event NotifyCollectionChangedEventHandler INotifyCollectionChanged.CollectionChanged
{
    add {
            CollectionChanged += value;
    }
    remove {
            CollectionChanged -= value;
    }
}

This implementation is explicit. So the event is hidden from normal access as a public member. To expose that member, you can either cast the instance to ICollectionView or INotifyPropertyChanged.

. When implementing an interface explicitly, you have to explicitly cast the instance to that interface before being able to access the interface members.

Example about implementing interface:

public interface IA {
   void Test();
}
//implicitly implement
public class A : IA {
   public void Test() { ... }
}
var a = new A();
a.Test();//you can do this


//explicitly implement
public class A : IA {
   void IA.Test() { ... } //note that there is no public and the interface name 
                          // is required
}
var a = new A();
((IA)a).Test(); //this is how you do it.