CollectionView.IndexOf Method (Object)
Returns the index at which the specified item is located.
Assembly: PresentationFramework (in PresentationFramework.dll)
If this method returns an index other than -1, it must always be true that view[index-1] < item <= view[index], where the comparisons are done using the IComparer.Compare method of the view, if one exists.
This particular behavior of the method is used by some CollectionChanged event handlers to speed up reaction to insertion and deletion. If the derived class does not override this method, a listener does a binary search using the IComparer.Compare method.
Available since 3.0