Duration (Pacific Standard Time):
To (Pacific Standard Time):
Impact:
User Action:

IOrderedDictionary Interface

 

Represents an indexed collection of key/value pairs.

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

Public Interface IOrderedDictionary
	Inherits IDictionary, ICollection, IEnumerable
Name Description
System_CAPS_pubproperty Count

Gets the number of elements contained in the ICollection.(Inherited from ICollection.)

System_CAPS_pubproperty IsFixedSize

Gets a value indicating whether the IDictionary object has a fixed size.(Inherited from IDictionary.)

System_CAPS_pubproperty IsReadOnly

Gets a value indicating whether the IDictionary object is read-only.(Inherited from IDictionary.)

System_CAPS_pubproperty IsSynchronized

Gets a value indicating whether access to the ICollection is synchronized (thread safe).(Inherited from ICollection.)

System_CAPS_pubproperty Item[Int32]

Gets or sets the element at the specified index.

System_CAPS_pubproperty Item[Object]

Gets or sets the element with the specified key.(Inherited from IDictionary.)

System_CAPS_pubproperty Keys

Gets an ICollection object containing the keys of the IDictionary object.(Inherited from IDictionary.)

System_CAPS_pubproperty SyncRoot

Gets an object that can be used to synchronize access to the ICollection.(Inherited from ICollection.)

System_CAPS_pubproperty Values

Gets an ICollection object containing the values in the IDictionary object.(Inherited from IDictionary.)

Name Description
System_CAPS_pubmethod Add(Object, Object)

Adds an element with the provided key and value to the IDictionary object.(Inherited from IDictionary.)

System_CAPS_pubmethod Clear()

Removes all elements from the IDictionary object.(Inherited from IDictionary.)

System_CAPS_pubmethod Contains(Object)

Determines whether the IDictionary object contains an element with the specified key.(Inherited from IDictionary.)

System_CAPS_pubmethod CopyTo(Array, Int32)

Copies the elements of the ICollection to an Array, starting at a particular Array index.(Inherited from ICollection.)

System_CAPS_pubmethod GetEnumerator()

Returns an enumerator that iterates through the IOrderedDictionary collection.

System_CAPS_pubmethod Insert(Int32, Object, Object)

Inserts a key/value pair into the collection at the specified index.

System_CAPS_pubmethod Remove(Object)

Removes the element with the specified key from the IDictionary object.(Inherited from IDictionary.)

System_CAPS_pubmethod RemoveAt(Int32)

Removes the element at the specified index.

Name Description
System_CAPS_pubmethod AsParallel()

Overloaded. Enables parallelization of a query.(Defined by ParallelEnumerable.)

System_CAPS_pubmethod AsQueryable()

Overloaded. Converts an IEnumerable to an IQueryable.(Defined by Queryable.)

System_CAPS_pubmethod Cast<TResult>()

Casts the elements of an IEnumerable to the specified type.(Defined by Enumerable.)

System_CAPS_pubmethod OfType<TResult>()

Filters the elements of an IEnumerable based on a specified type.(Defined by Enumerable.)

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.

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.

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 - 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
Universal Windows Platform
Available since 10
.NET Framework
Available since 2.0
Return to top