Building Dictionaries: The DictionaryBase Class and the SortedList Class

Abstract

A dictionary is a data structure that stores data as a key–value pair. The DictionaryBase class is used as an abstract class to implement different data structures that all store data as key–value pairs. These data structures can be hash tables, linked lists, or some other data structure type. In this chapter, we examine how to create basic dictionaries and how to use the inherited methods of the DictionaryBase class. We will use these techniques later when we explore more specialized data structures. One example of a dictionary-based data structure is the SortedList. This class stores key–value pairs in sorted order based on the key. It is an interesting data structure because you can also access the values stored in the structure by referring to the value's index position in the data structure, which makes the structure behave somewhat like an array. We examine the behavior of the SortedList class at the end of the chapter. THE DICTIONARYBASE CLASS You can think of a dictionary data structure as a computerized word dictionary. The word you are looking up is the key, and the definition of the word is the value. The DictionaryBase class is an abstract (MustInherit) class that is used as a basis for specialized dictionary implementations. The key–value pairs stored in a dictionary are actually stored as DictionaryEntry objects. The DictionaryEntry structure provides two fields, one for the key and one for the value.