C# 0 The Complete Reference

Dictionary 

defines these properties:

Property

Description

public IEqualityComparer

    Comparer { get; }

Obtains the comparer for the invoking dictionar y.

public Dictionar y.KeyCollection

    Keys { get; }

Obtains a collection of the keys.

public Dictionar y.ValueCollection

    Values { get; }

Obtains a collection of the values. 

Notice that the keys and values contained within the collection are available as separate lists 

through the 

Keys

 and 

Values

 properties. The types 

Dictionary.KeyCollection

and

Dictionary.ValueCollection 

are collections that implement both the generic 

and non-generic forms of 

ICollection

 and 

IEnumerable

.

The following indexer, defined by 

IDictionary

, is implemented by 

Dictionary

 as shown here:

public TV this[TK 

key

] { get; set; }

You can use this indexer to get or set the value of an element. You can also use it to add a 

new element to the collection. Notice that the “index” is not actually an index, but rather the 

key of the item.

When enumerating the collection, 

Dictionary

 returns key/value pairs in the 

form of a 

KeyValuePair

 structure. Recall that this structure defines the following 

two fields:

public TK Key;

public TV Value;

These fields hold the key or value associated with an entry. Most of the time you won’t need 

to use 

KeyValuePair

 directly because 

Dictionary

 allows you to work 

the keys and values individually. However, when enumerating a 

Dictionary

, such 

as in a 

foreach

 loop, the objects being enumerated are 

KeyValuePair

s.

In a 

Dictionary

, all keys must be unique, and a key must not change while it 

is in use as a key. Values need not be unique. The objects in a 

Dictionary

 are not 

stored in sorted order.

Here is an example that demonstrates 

Dictionary

:

// Demonstrate the generic Dictionary class.

using System;

using System.Collections.Generic;

class GenDictionaryDemo {

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