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.与Hashtable的区别，有次用Hashtable添加下拉值都对不上，要手动调，如果用这个就不用了
3.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();
        }
    }

}
参考：http://msdn.microsoft.com/zh-cn/library/system.collections.specialized.namevaluecollection(VS.80).aspx