Property Count
Count
Return the number of items (or -1, meaning "don't know"); if a Filter is set, this counts only items that pass the filter.
public virtual int Count { get; }
Property Value
Remarks
If the underlying collection is only of type IEnumerable, this count is a O(N) operation; this Count value will be cached until the collection changes again.
When deriving from CollectionView, override this property to provide a more efficient implementation.