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.NET Framework Class Library

IEnumerable Interface

Exposes an enumerator, which supports a simple iteration over a non-generic collection.

To browse the .NET Framework source code for this type, see the Reference Source.

Namespace:  System.Collections
Assembly:  mscorlib (in mscorlib.dll)
<GuidAttribute("496B0ABE-CDEE-11d3-88E8-00902754C43A")> _
<ComVisibleAttribute(True)> _
Public Interface IEnumerable

The IEnumerable type exposes the following members.

  Name Description
Public method Supported by the XNA Framework Supported by Portable Class Library GetEnumerator Returns an enumerator that iterates through a collection.
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  Name Description
Public Extension Method Supported by Portable Class Library AsParallel() Overloaded. Enables parallelization of a query. (Defined by ParallelEnumerable.)
Public Extension Method Supported by Portable Class Library AsParallel() Overloaded. (Defined by ParallelEnumerable.)
Public Extension Method Supported by Portable Class Library AsQueryable() Overloaded. Converts an IEnumerable to an IQueryable. (Defined by Queryable.)
Public Extension Method Supported by Portable Class Library AsQueryable() Overloaded. (Defined by Queryable.)
Public Extension Method Supported by the XNA Framework Supported by Portable Class Library Cast<TResult>() Overloaded. Casts the elements of an IEnumerable to the specified type. (Defined by Enumerable.)
Public Extension Method Supported by the XNA Framework Supported by Portable Class Library Cast<TResult>() Overloaded. (Defined by Enumerable.)
Public Extension Method Supported by the XNA Framework Supported by Portable Class Library OfType<TResult>() Overloaded. Filters the elements of an IEnumerable based on a specified type. (Defined by Enumerable.)
Public Extension Method Supported by the XNA Framework Supported by Portable Class Library OfType<TResult>() Overloaded. (Defined by Enumerable.)
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Note Note

To view the .NET Framework source code for this type, see the Reference Source. You can browse through the source code online, download the reference for offline viewing, and step through the sources (including patches and updates) during debugging; see instructions.

IEnumerable is the base interface for all non-generic collections that can be enumerated. For the generic version of this interface see System.Collections.Generic.IEnumerable<T>. IEnumerable contains a single method, GetEnumerator, which returns an IEnumerator. IEnumerator provides the ability to iterate through the collection by exposing a Current property and MoveNext and Reset methods.

It is a best practice to implement IEnumerable and IEnumerator on your collection classes to enable the foreach (For Each in Visual Basic) syntax, however implementing IEnumerable is not required. If your collection does not implement IEnumerable, you must still follow the iterator pattern to support this syntax by providing a GetEnumerator method that returns an interface, class or struct. When using Visual Basic, you must provide an IEnumerator implementation, which is returned by GetEnumerator. When developing with C# you must provide a class that contains a Current property, and MoveNext and Reset methods as described by IEnumerator, but the class does not have to implement IEnumerator.

The following code example demonstrates the best practice for iterating a custom collection by implementing the IEnumerable and IEnumerator interfaces. In this example, members of these interfaces are not explicitly called, but they are implemented to support the use of foreach (For Each in Visual Basic) to iterate through the collection. This example is a complete Console app. To compile the Visual Basic app, change the Startup object to Sub Main in the project’s Properties page.

For a sample that shows how to implement the IEnumerable interface, see Implementing the IEnumerable Interface in a Collection Class

Imports System
Imports System.Collections

' Simple business object. 
Public Class Person

    Public Sub New(ByVal fName As String, ByVal lName As String)
        Me.firstName = fName
        Me.lastName = lName
    End Sub 


    Public firstName As String 
    Public lastName As String 
End Class 

' Collection of Person objects, which implements IEnumerable so that 
' it can be used with ForEach syntax. 
Public Class People
    Implements IEnumerable

    Private _people() As Person

    Public Sub New(ByVal pArray() As Person)
        _people = New Person(pArray.Length - 1) {}

        Dim i As Integer 
        For i = 0 To pArray.Length - 1
            _people(i) = pArray(i)
        Next i
    End Sub 

    ' Implementation of GetEnumerator. 
    Public Function GetEnumerator() As IEnumerator _
      Implements IEnumerable.GetEnumerator

        Return New PeopleEnum(_people)
    End Function 

End Class 

' When you implement IEnumerable, you must also implement IEnumerator. 
Public Class PeopleEnum
    Implements IEnumerator

    Public _people() As Person

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

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

    Public Function MoveNext() As Boolean Implements IEnumerator.MoveNext
        position = position + 1
        Return (position < _people.Length)
    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 ex As IndexOutOfRangeException
                Throw New InvalidOperationException()
            End Try 
        End Get 
    End Property 
End Class 

Class App
    Shared Sub Main()
        Dim peopleArray() As Person = { _
            New Person("John", "Smith"), _
            New Person("Jim", "Johnson"), _
            New Person("Sue", "Rabon")}

        Dim peopleList As New People(peopleArray)
        Dim p As Person
        For Each p In peopleList
            Console.WriteLine(p.firstName + " " + p.lastName)
        Next 

    End Sub 
End Class 

' This code produces output similar to the following: 
'  
' John Smith 
' Jim Johnson 
' Sue Rabon

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library