.NET C#: NameValueCollection

NameValueCollection class is in System.Collection.Specialized assembly.

Unlike with HashTable, NameValueCollection can have more than one values for one key.

So there is no error for code below:

NameValueCollection myCol = new NameValueCollection();

myCol.Add("red", "rojo");

myCol.Add("red", "rouge");

while using HashTable there will be an error.

Let us see some demo:

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

 public class ConsoleTest
 {

     public static void Main()
     {

         // Creates and initializes a new NameValueCollection.
         NameValueCollection myCol = new NameValueCollection();
         myCol.Add("red", "rojo");
         myCol.Add("green", "verde");
         myCol.Add("blue", "azul");
         myCol.Add("red", "rouge");

         // Displays the values in the NameValueCollection in two different ways.
         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.
         Console.WriteLine("Index 1 contains the value {0}.", myCol[1]);
         Console.WriteLine("Key \"red\" has the value {0}.", myCol["red"]);
         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();

         // Searches for a key and deletes it.
         myCol.Remove("green");
         Console.WriteLine("The collection contains the following elements after removing \"green\":");
         PrintKeysAndValues(myCol);

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

     }

     public static void PrintKeysAndValues(NameValueCollection myCol)
     {
         Console.WriteLine("   KEY        VALUE");
         foreach (String s in myCol.AllKeys)
             Console.WriteLine("   {0,-10} {1}", s, myCol[s]);
         Console.WriteLine();
     }

     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();
     }

 }

 /*

 This code produces the following output.

 Displays the elements using the AllKeys property and the Item (indexer) property:
    KEY        VALUE
    red        rojo,rouge
    green      verde
    blue       azul

 Displays the elements using GetKey and Get:
    [INDEX] KEY        VALUE
    [0]     red        rojo,rouge
    [1]     green      verde
    [2]     blue       azul

 Index 1 contains the value verde.
 Key "red" has the value rojo,rouge.

 The string array contains:
    rojo,rouge
    verde
    azul

 The collection contains the following elements after removing "green":
    KEY        VALUE
    red        rojo,rouge
    blue       azul

 The collection contains the following elements after it is cleared:
    KEY        VALUE

 */

reference: https://msdn.microsoft.com/zh-cn/library/system.collections.specialized.namevaluecollection.aspx