.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