1.NameValueCollection类集合是基于 NameObjectCollectionBase 类。
但与 NameObjectCollectionBase 不同，该类在一个键下存储多个字符串值（就是键相同，值就连接起来如下例子）。该类可用于标头、查询字符串和窗体数据。
每个元素都是一个键/值对。NameValueCollection 的容量是 NameValueCollection 可以保存的元素数。
NameValueCollection 的默认初始容量为零。随着向 NameValueCollection 中添加元素，容量通过重新分配按需自动增加。
如下例子：

NameValueCollection myCol = new NameValueCollection();
myCol.Add("red", "rojo");//如果键值red相同结果合并 rojo,rouge
myCol.Add("green", "verde");
myCol.Add("blue", "azul");
myCol.Add("red", "rouge");

2.NameValueCollection与Hashtable的区别
a.引用区别

hashtable:using System.Collections;

NameValueCollection:using System.Collections.Specialized;

b.键是否重复

NameValueCollection:允许重复.

HashTable是键-值集合,但键不能出现重复.

Hashtable ht = new Hashtable();
ht.Add("key","value");
ht.Add("key", "value1"); //出错
ht["key"] = "value1"; //正确

3.初始化NameValueCollection
初始化NameValueCollection需引用using System.Collections.Specialized;
完整例子源码：

using System; using System.Collections;
using System.Collections.Specialized;

namespace SamplesNameValueCollection
{
class Program
{

public static void Main()
{
//初始化NameValueCollection需引用using System.Collections.Specialized;
NameValueCollection myCol = new NameValueCollection();
myCol.Add("red", "rojo");//如果键值red相同结果合并 rojo,rouge
myCol.Add("green", "verde");
myCol.Add("blue", "azul");
myCol.Add("red", "rouge");

// Displays the values in the NameValueCollection in two different ways.
//显示键，值
Console.WriteLine("Displays the elements using the AllKeys property and the Item (indexer) property:");
PrintKeysAndValues(myCol);
Console.WriteLine("Displays the elements using GetKey and Get:");
PrintKeysAndValues2(myCol);

// Gets a value either by index or by key.
//按索引或值获取
Console.WriteLine("Index 1 contains the value {0}.", myCol[1]);//索引1的值
Console.WriteLine("Key \"red\" has the value {0}.", myCol["red"]);//键为red的对应值rouge
Console.WriteLine();

// Copies the values to a string array and displays the string array.
String[] myStrArr = new String[myCol.Count];
myCol.CopyTo(myStrArr, 0);
Console.WriteLine("The string array contains:");
foreach (String s in myStrArr)
Console.WriteLine(" {0}", s);
Console.WriteLine();

//查找green键值然后删除
myCol.Remove("green");
Console.WriteLine("The collection contains the following elements after removing \"green\":");
PrintKeysAndValues(myCol);

//清空集合
myCol.Clear();
Console.WriteLine("The collection contains the following elements after it is cleared:");
PrintKeysAndValues(myCol);

}
//显示键，值
public static void PrintKeysAndValues(NameValueCollection myCol)
{
IEnumerator myEnumerator = myCol.GetEnumerator();
Console.WriteLine(" KEY VALUE");
foreach (String s in myCol.AllKeys)
Console.WriteLine(" {0,-10} {1}", s, myCol[s]);
Console.WriteLine();
}
//显示索引, 键,值
public static void PrintKeysAndValues2(NameValueCollection myCol)
{
Console.WriteLine(" [INDEX] KEY VALUE");
for (int i = 0; i < myCol.Count; i++)
Console.WriteLine(" [{0}] {1,-10} {2}", i, myCol.GetKey(i), myCol.Get(i));
Console.WriteLine();
}
}

}
4.NameValueCollection遍历
与Hashtable相似:

NameValueCollection myCol = new NameValueCollection();
myCol.Add("red", "rojo");//如果键值red相同结果合并 rojo,rouge
myCol.Add("green", "verde");
myCol.Add("blue", "azul");
myCol["red"] = "dd";

foreach (string key in myCol.Keys)
{
Console.WriteLine("{0}:{1}", key, myCol[key]);
}
Console.ReadLine();