A helper class for adapters that implement the SectionIndexer interface. If the items in the adapter are sorted by simple alphabet-based sorting, then this class provides a way to do fast indexing of large lists using binary search. It caches the indices that have been determined through the binary search and also invalidates the cache if changes occur in the cursor.

Your adapter is responsible for updating the cursor by calling AlphabetIndexer.SetCursor(Android.Database.ICursor) if the cursor changes. AlphabetIndexer.GetPositionForSection(int) method does the binary search for the starting index of a given section (alphabet).

[Android Documentation]