数据字典是什么呀？？谁能举个最简单的例子？？是例子哦！！

Dictionary,表示键和值的集合。
用泛型类举例吧
Dictionary) 泛型类
using System;
using System.Collections.Generic;

public class Example
{
public static void Main()
{
// Create a new dictionary of strings, with string keys.
//
Dictionary openWith =
new Dictionary();

// Add some elements to the dictionary. There are no
// duplicate keys, but some of the values are duplicates.
openWith.Add(txt, notepad.exe);
openWith.Add(bmp, paint.exe);
openWith.Add(dib, paint.exe);
openWith.Add(rtf, wordpad.exe);

// The Add method throws an exception if the new key is
// already in the dictionary.
try
{
openWith.Add(txt, winword.exe);
}
catch (ArgumentException)
{
Console.WriteLine(An element with Key = txt already exists.);
}

// The Item property is another name for the indexer, so you
// can omit its name when accessing elements.
Console.WriteLine(For key = rtf, value = {0}.,
openWith[rtf]);

// The indexer can be used to change the value associated
// with a key.
openWith[rtf] = winword.exe;
Console.WriteLine(For key = rtf, value = {0}.,
openWith[rtf]);

// If a key does not exist, setting the indexer for that key
// adds a new key/value pair.
openWith[doc] = winword.exe;

// The indexer throws an exception if the requested key is
// not in the dictionary.
try
{
Console.WriteLine(For key = tif, value = {0}.,
openWith[tif]);
}
catch (KeyNotFoundException)
{
Console.WriteLine(Key = tif is not found.);
}

// When a program often has to try keys that turn out not to
// be in the dictionary, TryGetValue can be a more efficient
// way to retrieve values.
string value = ;
if (openWith.TryGetValue(tif, out value))
{
Console.WriteLine(For key = tif, value = {0}., value);
}
else
{
Console.WriteLine(Key = tif is not found.);
}

// ContainsKey can be used to test keys before inserting
// them.
if (!openWith.ContainsKey(ht))
{
openWith.Add(ht, hypertrm.exe);
Console.WriteLine(Value added for key = ht: {0},
openWith[ht]);
}

// When you use foreach to enumerate dictionary elements,
// the elements are retrieved as KeyValuePair objects.
Console.WriteLine();
foreach( KeyValuePair kvp in openWith )
{
Console.WriteLine(Key = {0}, Value = {1},
kvp.Key, kvp.Value);
}

// To get the values alone, use the Values property.
Dictionary.ValueCollection valueColl =
openWith.Values;

// The elements of the ValueCollection are strongly typed
// with the type that was specified for dictionary values.
Console.WriteLine();
foreach( string s in valueColl )
{
Console.WriteLine(Value = {0}, s);
}

// To get the keys alone, use the Keys property.
Dictionary.KeyCollection keyColl =
openWith.Keys;

// The elements of the KeyCollection are strongly typed
// with the type that was specified for dictionary keys.
Console.WriteLine();
foreach( string s in keyColl )
{
Console.WriteLine(Key = {0}, s);
}

// Use the Remove method to remove a key/value pair.
Console.WriteLine(nRemove(doc));
openWith.Remove(doc);

if (!openWith.ContainsKey(doc))
{
Console.WriteLine(Key doc is not found.);
}
}
}