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();