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IOrderedDictionary Interface

Represents an indexed collection of key/value pairs.

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

public interface IOrderedDictionary : IDictionary, ICollection, IEnumerable
public interface IOrderedDictionary extends IDictionary, ICollection, 
	IEnumerable
public interface IOrderedDictionary extends IDictionary, ICollection, 
	IEnumerable
Not applicable.

IOrderedDictionary elements can be accessed either with the key or with the index.

Each element is a key/value pair stored in a DictionaryEntry structure.

Each pair must have a unique key that is not a null reference (Nothing in Visual Basic), but the value can be a null reference (Nothing in Visual Basic) and does not have to be unique. The IOrderedDictionary interface allows the contained keys and values to be enumerated, but it does not imply any particular sort order.

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 IDictionary 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. For example:

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

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

Notes to Implementers: The implementing class must have a means to compare keys.

The following code example demonstrates the implementation of a simple IOrderedDictionary based on the ArrayList class. The implemented IOrderedDictionary stores first names as the keys and last names as the values, with the added requirement that each first name is unique.

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

public class People : IOrderedDictionary
{
    private ArrayList _people;

    public People(int numItems)
    {
        _people = new ArrayList(numItems);
    }

    public int IndexOfKey(object key)
    {
        for (int i = 0; i < _people.Count; i++)
        {
            if (((DictionaryEntry)_people[i]).Key == key)
                return i;
        }

        // key not found, reutrn -1.
        return -1;
    }

    public object this[object key]
    {
        get
        {
            return ((DictionaryEntry)_people[IndexOfKey(key)]).Value;
        }
        set
        {
            _people[IndexOfKey(key)] = new DictionaryEntry(key, value);
        }
    }

    // IOrderedDictionary Members
    public IDictionaryEnumerator GetEnumerator()
    {
        return new PeopleEnum(_people);
    }

    public void Insert(int index, object key, object value)
    {
        if (IndexOfKey(key) != -1)
        {
            throw new ArgumentException("An element with the same key already exists in the collection.");
        }
        _people.Insert(index, new DictionaryEntry(key, value));
    }

    public void RemoveAt(int index)
    {
        _people.RemoveAt(index);
    }

    public object this[int index]
    {
        get
        {
            return ((DictionaryEntry)_people[index]).Value;
        }
        set
        {
            object key = ((DictionaryEntry)_people[index]).Key;
            _people[index] = new DictionaryEntry(Keys, value);
        }
    }
    // IDictionary Members

    public void Add(object key, object value)
    {
        if (IndexOfKey(key) != -1)
        {
            throw new ArgumentException("An element with the same key already exists in the collection.");
        }
        _people.Add(new DictionaryEntry(key, value));
    }

    public void Clear()
    {
        _people.Clear();
    }

    public bool Contains(object key)
    {
        if (IndexOfKey(key) == -1)
        {
            return false;
        }
        else
        {
            return true;
        }
    }

    public bool IsFixedSize
    {
        get
        {
            return false;
        }
    }

    public bool IsReadOnly
    {
        get
        {
            return false;
        }
    }

    public ICollection Keys
    {
        get
        {
            ArrayList KeyCollection = new ArrayList(_people.Count);
            for (int i = 0; i < _people.Count; i++)
            {
                KeyCollection[i] = ((DictionaryEntry)_people[i]).Key;
            }
            return KeyCollection;
        }
    }

    public void Remove(object key)
    {
        _people.RemoveAt(IndexOfKey(key));
    }

    public ICollection Values
    {
        get
        {
            ArrayList ValueCollection = new ArrayList(_people.Count);
            for (int i = 0; i < _people.Count; i++)
            {
                ValueCollection[i] = ((DictionaryEntry)_people[i]).Value;
            }
            return ValueCollection;
        }
    }


    // ICollection Members

    public void CopyTo(Array array, int index)
    {
        _people.CopyTo(array, index);
    }

    public int Count
    {
        get
        {
            return _people.Count;
        }
    }

    public bool IsSynchronized
    {
        get
        {
            return _people.IsSynchronized;
        }
    }

    public object SyncRoot
    {
        get
        {
            return _people.SyncRoot;
        }
    }

    // IEnumerable Members

    IEnumerator IEnumerable.GetEnumerator()
    {
        return new PeopleEnum(_people);
    }
}

public class PeopleEnum : IDictionaryEnumerator
{
    public ArrayList _people;
    
    // Enumerators are positioned before the first element
    // until the first MoveNext() call.
    int position = -1;

    public PeopleEnum(ArrayList list)
    {
        _people = list;
    }

    public bool MoveNext()
    {
        position++;
        return (position < _people.Count);
    }

    public void Reset()
    {
        position = -1;
    }

    public object Current
    {
        get
        {
            try
            {
                return _people[position];
            }
            catch (IndexOutOfRangeException)
            {
                throw new InvalidOperationException();
            }
        }
    }

    public DictionaryEntry Entry
    {
        get
        {
            return (DictionaryEntry)Current;
        }
    }

    public object Key
    {
        get
        {
            try
            {
                return ((DictionaryEntry)_people[position]).Key;
            }
            catch (IndexOutOfRangeException)
            {
                throw new InvalidOperationException();
            }
        }
    }

    public object Value
    {
        get
        {
            try
            {
                return ((DictionaryEntry)_people[position]).Value;
            }
            catch (IndexOutOfRangeException)
            {
                throw new InvalidOperationException();
            }
        }
    }
}

class App
{
    static void Main()
    {
        People peopleCollection = new People(3);
        peopleCollection.Add("John", "Smith");
        peopleCollection.Add("Jim", "Johnson");
        peopleCollection.Add("Sue", "Rabon");

        Console.WriteLine("Displaying the entries in peopleCollection:");
        foreach (DictionaryEntry de in peopleCollection)
        {
            Console.WriteLine("{0} {1}", de.Key, de.Value);
        }

        Console.WriteLine();
        Console.WriteLine("Displaying the entries in the modified peopleCollection:");
        peopleCollection["Jim"] = "Jackson";
        peopleCollection.Remove("Sue");
        peopleCollection.Insert(0, "Fred", "Anderson");

        foreach (DictionaryEntry de in peopleCollection)
        {
            Console.WriteLine("{0} {1}", de.Key, de.Value);
        }
    }
}
/* This code produces output similar to the following:
 * 
 * Displaying the entries in peopleCollection:
 * John Smith
 * Jim Johnson
 * Sue Rabon
 * 
 * Displaying the entries in the modified peopleCollection:
 * Fred Anderson
 * John Smith
 * Jim Jackson
 */

Windows 98, Windows Server 2000 SP4, Windows Millennium Edition, 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

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