NameValueCollection详解

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();