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IOrderedDictionary Interface

Represents an indexed collection of key/value pairs.

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

'Declaration
Public Interface IOrderedDictionary _
	Inherits IDictionary, ICollection, IEnumerable
'Usage
Dim instance As IOrderedDictionary

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 Nothing, but the value can be Nothing 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.

[Visual Basic, C#]

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:

For Each de As DictionaryEntry In myOrderedDictionary
  ...
Next de

[Visual Basic, C#]

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.

Imports System
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
                KeyCollection(i) = 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
                ValueCollection(i) = 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

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

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