SortedList Collection Type
As with Hashtable, SortedList is based on the IDictionary interface; therefore, each element of a SortedList is a key-and-value pair. SortedList provides methods that return only the list of keys or only the list of values.
As with ArrayList, a SortedList is a sequence of elements. It is indexed, and is sorted according to a specified comparer.
SortedList is unique among all Collections classes in that each element can be accessed three ways: using the key, the value, or the index.
Use SortedList if you want a collection that holds key-and-value pairs but also need the flexibility of an indexed list.