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OrderedDictionary Class

Represents a collection of key/value pairs that are accessible by the key or index.

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

public class OrderedDictionary : IOrderedDictionary, 
	IDictionary, ICollection, IEnumerable, ISerializable, IDeserializationCallback

Each element is a key/value pair stored in a DictionaryEntry object. A key cannot be null, but a value can be.

The elements of an OrderedDictionary are not sorted in any way. OrderedDictionary collections allow access by both index as well as key.

The foreach statement of the C# language (For Each in Visual Basic) requires the type of each element in the collection. Since each element of the OrderedDictionary collection is a key/value pair, the element type is not the type of the key or the type of the value. Instead, the element type is DictionaryEntry. The following code shows C# and Visual Basic syntax.

foreach (DictionaryEntry de in myListDictionary) {...}

[Visual Basic, C#]

The foreach statement is a wrapper around the enumerator, which only allows reading from, not writing to, the collection.

The following code example demonstrates the creation, population and modification of an OrderedDictionary collection, as well as two techniques to display the contents of the OrderedDictionary: one using the Keys and Values properties and the other creating an enumerator through the GetEnumerator method.

// The following code example enumerates the elements of a OrderedDictionary. 
using System;
using System.Collections;
using System.Collections.Specialized;

public class OrderedDictionarySample
    public static void Main()

        // Creates and initializes a OrderedDictionary.
        OrderedDictionary myOrderedDictionary = new OrderedDictionary();
        myOrderedDictionary.Add("testKey1", "testValue1");
        myOrderedDictionary.Add("testKey2", "testValue2");
        myOrderedDictionary.Add("keyToDelete", "valueToDelete");
        myOrderedDictionary.Add("testKey3", "testValue3");

        ICollection keyCollection = myOrderedDictionary.Keys;
        ICollection valueCollection = myOrderedDictionary.Values;

        // Display the contents using the key and value collections
        DisplayContents(keyCollection, valueCollection, myOrderedDictionary.Count);

        // Modifying the OrderedDictionary 
        if (!myOrderedDictionary.IsReadOnly)
            // Insert a new key to the beginning of the OrderedDictionary
            myOrderedDictionary.Insert(0, "insertedKey1", "insertedValue1");

            // Modify the value of the entry with the key "testKey2"
            myOrderedDictionary["testKey2"] = "modifiedValue";

            // Remove the last entry from the OrderedDictionary: "testKey3"
            myOrderedDictionary.RemoveAt(myOrderedDictionary.Count - 1);

            // Remove the "keyToDelete" entry, if it exists
            if (myOrderedDictionary.Contains("keyToDelete"))

            "{0}Displaying the entries of a modified OrderedDictionary.",
        DisplayContents(keyCollection, valueCollection, myOrderedDictionary.Count);

        // Clear the OrderedDictionary and add new values
        myOrderedDictionary.Add("newKey1", "newValue1");
        myOrderedDictionary.Add("newKey2", "newValue2");
        myOrderedDictionary.Add("newKey3", "newValue3");

        // Display the contents of the "new" Dictionary using an enumerator
        IDictionaryEnumerator myEnumerator =

            "{0}Displaying the entries of a \"new\" OrderedDictionary.",



    // Displays the contents of the OrderedDictionary from its keys and values 
    public static void DisplayContents(
        ICollection keyCollection, ICollection valueCollection, int dictionarySize)
        String[] myKeys = new String[dictionarySize];
        String[] myValues = new String[dictionarySize];
        keyCollection.CopyTo(myKeys, 0);
        valueCollection.CopyTo(myValues, 0);

        // Displays the contents of the OrderedDictionary
        Console.WriteLine("   INDEX KEY                       VALUE");
        for (int i = 0; i < dictionarySize; i++)
            Console.WriteLine("   {0,-5} {1,-25} {2}",
                i, myKeys[i], myValues[i]);

    // Displays the contents of the OrderedDictionary using its enumerator 
    public static void DisplayEnumerator(IDictionaryEnumerator myEnumerator)
        Console.WriteLine("   KEY                       VALUE");
        while (myEnumerator.MoveNext())
            Console.WriteLine("   {0,-25} {1}",
                myEnumerator.Key, myEnumerator.Value);

This code produces the following output.

   INDEX KEY                       VALUE
   0     testKey1                  testValue1
   1     testKey2                  testValue2
   2     keyToDelete               valueToDelete
   3     testKey3                  testValue3

Displaying the entries of a modified OrderedDictionary.
   INDEX KEY                       VALUE
   0     insertedKey1              insertedValue1
   1     testKey1                  testValue1
   2     testKey2                  modifiedValue

Displaying the entries of a "new" OrderedDictionary.
   KEY                       VALUE
   newKey1                   newValue1
   newKey2                   newValue2
   newKey3                   newValue3



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

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Supported in: 3.5, 3.0, 2.0