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NameValueCollection Class

Represents a collection of associated String keys and String values that can be accessed either with the key or with the index.

Namespace: System.Collections.Specialized
Assembly: System (in system.dll)

[SerializableAttribute] 
public class NameValueCollection : NameObjectCollectionBase
/** @attribute SerializableAttribute() */ 
public class NameValueCollection extends NameObjectCollectionBase
SerializableAttribute 
public class NameValueCollection extends NameObjectCollectionBase
Not applicable.

This collection is based on the NameObjectCollectionBase class. However, unlike the NameObjectCollectionBase, this class stores multiple string values under a single key.

This class can be used for headers, query strings and form data.

Each element is a key/value pair.

The capacity of a NameValueCollection is the number of elements the NameValueCollection can hold. As elements are added to a NameValueCollection, the capacity is automatically increased as required through reallocation.

The hash code provider dispenses hash codes for keys in the NameValueCollection. The default hash code provider is the CaseInsensitiveHashCodeProvider.

The comparer determines whether two keys are equal. The default comparer is the CaseInsensitiveComparer.

In .NET Framework version 1.0, this class uses culture-sensitive string comparisons. However, in .NET Framework version 1.1 and later, this class uses CultureInfo.InvariantCulture when comparing strings. For more information about how culture affects comparisons and sorting, see Comparing and Sorting Data for a Specific CultureComparing and Sorting Data for a Specific Cultureand Performing Culture-Insensitive String Operations.

a null reference (Nothing in Visual Basic) is allowed as a key or as a value.

Caution noteCaution:

The Get method does not distinguish between a null reference (Nothing in Visual Basic) which is returned because the specified key is not found and a null reference (Nothing in Visual Basic) which is returned because the value associated with the key is a null reference (Nothing in Visual Basic).

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How to: Read Application Settings from the Web.config FileConfiguring ASP .NET Web Applications
How to: Read Application Settings from the Web.config FileConfiguring ASP .NET Web Applications
using System;
using System.Collections;
using System.Collections.Specialized;

public class SamplesNameValueCollection  {

   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 )  {
      IEnumerator myEnumerator = myCol.GetEnumerator();
      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


*/

import System.*;
import System.Collections.*;
import System.Collections.Specialized.*;

public class SamplesNameValueCollection
{
    public static void main(String[] args)
    {
        // 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.get_Item(1));
        Console.WriteLine("Key \"red\" has the value {0}.",
            myCol.get_Item("red"));
        Console.WriteLine();
        // Copies the values to a string array and displays the string array.
        String myStrArr[] = new String[myCol.get_Count()];
        myCol.CopyTo(myStrArr, 0);
        Console.WriteLine("The string array contains:");
        for (int iCtr = 0; iCtr < myStrArr.get_Length(); iCtr++) {
            String s = myStrArr[iCtr];
            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);
    } //main

    public static void PrintKeysAndValues(NameValueCollection myCol)
    {
        IEnumerator myEnumerator = myCol.GetEnumerator();
        Console.WriteLine("   KEY        VALUE");
        for (int iCtr = 0; iCtr < myCol.get_Count(); iCtr++) {
            String s = myCol.get_AllKeys()[iCtr];
            Console.WriteLine("   {0,-10} {1}", s, myCol.get_Item(s));
        }
        Console.WriteLine();
    } //PrintKeysAndValues

    public static void PrintKeysAndValues2(NameValueCollection myCol)
    {
        Console.WriteLine("   [INDEX] KEY        VALUE");
        for (int i = 0; i < myCol.get_Count(); i++) {
            Console.WriteLine("   [{0}]     {1,-10} {2}",
                System.Convert.ToString(i), System.Convert.ToString(
                myCol.GetKey(i)), System.Convert.ToString(myCol.Get(i)));
        }
        Console.WriteLine();
    } //PrintKeysAndValues2
} //SamplesNameValueCollection 

/*
    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       
*/

Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

This implementation does not provide a synchronized (thread safe) wrapper for a NameValueCollection, but derived classes can create their own synchronized versions of the NameValueCollection using the SyncRoot property of the NameObjectCollectionBase class.

Enumerating through a collection is intrinsically not a thread safe procedure. Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception. To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

XNA Framework

Supported in: 1.0
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