IOrderedDictionary Interface

Definition

public interface class IOrderedDictionary : System::Collections::IDictionary

public interface IOrderedDictionary : System.Collections.IDictionary

type IOrderedDictionary = interface
    interface ICollection
    interface IEnumerable
    interface IDictionary

type IOrderedDictionary = interface
    interface IDictionary
    interface ICollection
    interface IEnumerable

Public Interface IOrderedDictionary
Implements IDictionary

Derived

System.Collections.Specialized.OrderedDictionary

Implements

ICollection IDictionary IEnumerable

Examples

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, return -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(key, 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.Add( ((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.Add( ((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
 */

Imports System.Collections
Imports System.Collections.Specialized

Public Class People
    Implements IOrderedDictionary
    Private _people As ArrayList

    Public Sub New(ByVal numItems As Integer)
        _people = New ArrayList(numItems)
    End Sub

    Public Function IndexOfKey(ByVal key As Object) As Integer
        Dim i As Integer
        For i = 0 To _people.Count - 1
            If CType(_people(i), DictionaryEntry).Key = key Then
                Return i
            End If
        Next i

        ' key not found, return -1.
        Return -1
    End Function

    ' IOrderedDictionary Members
    Public Function GetEnumerator() As IDictionaryEnumerator _
        Implements IOrderedDictionary.GetEnumerator

        Return New PeopleEnum(_people)
    End Function

    Public Sub Insert(ByVal index As Integer, ByVal key As Object, _
        ByVal value As Object) Implements IOrderedDictionary.Insert

        If Not IndexOfKey(key) = -1 Then
            Throw New ArgumentException("An element with the same key already exists in the collection.")
        End If
        _people.Insert(index, New DictionaryEntry(key, value))
    End Sub

    Public Sub RemoveAt(ByVal index As Integer) _
        Implements IOrderedDictionary.RemoveAt

        _people.RemoveAt(index)
    End Sub

    Public Property Item(ByVal index As Integer) As Object _
        Implements IOrderedDictionary.Item

        Get
            Return CType(_people(index), DictionaryEntry).Value
        End Get
        Set(ByVal value As Object)
            Dim key As Object = CType(_people(index), DictionaryEntry).Key
            _people(index) = New DictionaryEntry(key, value)
        End Set
    End Property

    ' IDictionary Members
    Public Function IDictionaryGetEnumerator() As IDictionaryEnumerator _
    Implements IDictionary.GetEnumerator

        Return New PeopleEnum(_people)
    End Function

    Public Property Item(ByVal key As Object) As Object _
        Implements IDictionary.Item

        Get
            Return CType(_people(IndexOfKey(key)), DictionaryEntry).Value
        End Get
        Set(ByVal value)
            _people(IndexOfKey(key)) = New DictionaryEntry(key, value)
        End Set
    End Property


    Public Sub Add(ByVal key As Object, ByVal value As Object) _
        Implements IDictionary.Add

        If Not IndexOfKey(key) = -1 Then
            Throw New ArgumentException("An element with the same key already exists in the collection.")
        End If

        _people.Add(New DictionaryEntry(key, value))
    End Sub

    Public Sub Clear() Implements IDictionary.Clear
        _people.Clear()
    End Sub

    Public Function Contains(ByVal key As Object) As Boolean _
        Implements IDictionary.Contains

        If IndexOfKey(key) = -1 Then
            Return False
        Else
            Return True
        End If
    End Function

    Public ReadOnly Property IsFixedSize() As Boolean _
        Implements IDictionary.IsFixedSize

        Get
            Return False
        End Get
    End Property

    Public ReadOnly Property IsReadOnly() As Boolean _
        Implements IDictionary.IsReadOnly
        Get
            Return False
        End Get
    End Property

    Public ReadOnly Property Keys() As ICollection _
        Implements IDictionary.Keys
        Get
            Dim KeyCollection As ArrayList = New ArrayList(_people.Count)
            Dim i As Integer
            For i = 0 To _people.Count - 1
                KeyCollection.Add( CType(_people(i), DictionaryEntry).Key )
            Next i
            Return KeyCollection
        End Get
    End Property

    Public Sub Remove(ByVal key As Object) _
        Implements IDictionary.Remove

        _people.RemoveAt(IndexOfKey(key))
    End Sub

    Public ReadOnly Property Values() As ICollection _
        Implements IDictionary.Values
        Get
            Dim ValueCollection As ArrayList = New ArrayList(_people.Count)
            Dim i As Integer
            For i = 0 To _people.Count - 1
                ValueCollection.Add( CType(_people(i), DictionaryEntry).Value )
            Next i
            Return ValueCollection
        End Get
    End Property

    ' ICollection Members
    Public Sub CopyTo(ByVal array As Array, ByVal index As Integer) _
    Implements ICollection.CopyTo

        _people.CopyTo(Array, index)
    End Sub

    Public ReadOnly Property Count() As Integer _
        Implements ICollection.Count

        Get
            Return _people.Count
        End Get
    End Property

    Public ReadOnly Property IsSynchronized() As Boolean _
        Implements ICollection.IsSynchronized

        Get
            Return _people.IsSynchronized
        End Get
    End Property

    Public ReadOnly Property SyncRoot() As Object _
        Implements ICollection.SyncRoot

        Get
            Return _people.SyncRoot
        End Get
    End Property

    ' IEnumerable Members
    Public Function IEnumerableGetEnumerator() As IEnumerator _
        Implements IEnumerable.GetEnumerator

        Return New PeopleEnum(_people)
    End Function
End Class

Public Class PeopleEnum
    Implements IDictionaryEnumerator

    Public _people As ArrayList

    ' Enumerators are positioned before the first element
    ' until the first MoveNext() call.
    Dim position As Integer = -1

    Public Sub New(ByVal list As ArrayList)
        _people = list
    End Sub

    Public Function MoveNext() As Boolean _
        Implements IEnumerator.MoveNext

        position = position + 1
        Return (position < _people.Count)
    End Function

    Public Sub Reset() _
        Implements IEnumerator.Reset

        position = -1
    End Sub

    Public ReadOnly Property Current() As Object _
        Implements IEnumerator.Current

        Get
            Try
                Return _people(position)
            Catch e As IndexOutOfRangeException
                Throw New InvalidOperationException()
            End Try
        End Get
    End Property

    Public ReadOnly Property Entry() As DictionaryEntry _
        Implements IDictionaryEnumerator.Entry
        Get
            Return CType(Current, DictionaryEntry)
        End Get
    End Property

    Public ReadOnly Property Key() As Object _
        Implements IDictionaryEnumerator.Key

        Get
            Try
                Return CType(_people(position), DictionaryEntry).Key
            Catch e As IndexOutOfRangeException
                Throw New InvalidOperationException()
            End Try
        End Get
    End Property

    Public ReadOnly Property Value() As Object _
        Implements IDictionaryEnumerator.Value

        Get
            Try
                Return CType(_people(position), DictionaryEntry).Value
            Catch e As IndexOutOfRangeException
                Throw New InvalidOperationException()
            End Try
        End Get
    End Property
End Class

Class App
    Shared Sub Main()
        Dim peopleCollection As People = New People(3)
        peopleCollection.Add("John", "Smith")
        peopleCollection.Add("Jim", "Johnson")
        peopleCollection.Add("Sue", "Rabon")

        Console.WriteLine("Displaying the entries in peopleCollection:")
        Dim de As DictionaryEntry
        For Each de In peopleCollection
            Console.WriteLine("{0} {1}", de.Key, de.Value)
        Next

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

        For Each de In peopleCollection
            Console.WriteLine("{0} {1}", de.Key, de.Value)
        Next
    End Sub
End Class
' 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

Remarks

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 null, but the value can be null 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) returns an object of the type of the elements in the collection. Because 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, as the following example shows.

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

For Each de In myOrderedDictionary
    '...
Next

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.

See also

• ICollection
• IDictionary