IEnumerable Interface

Definition

public interface class IEnumerable

public interface IEnumerable

[System.Runtime.InteropServices.Guid("496B0ABE-CDEE-11d3-88E8-00902754C43A")]
public interface IEnumerable

[System.Runtime.InteropServices.Guid("496B0ABE-CDEE-11d3-88E8-00902754C43A")]
[System.Runtime.InteropServices.ComVisible(true)]
public interface IEnumerable

type IEnumerable = interface

[<System.Runtime.InteropServices.Guid("496B0ABE-CDEE-11d3-88E8-00902754C43A")>]
type IEnumerable = interface

[<System.Runtime.InteropServices.Guid("496B0ABE-CDEE-11d3-88E8-00902754C43A")>]
[<System.Runtime.InteropServices.ComVisible(true)>]
type IEnumerable = interface

Public Interface IEnumerable

Derived

Microsoft.Extensions.AI.AdditionalPropertiesDictionary<TValue>

Microsoft.Extensions.AI.AIFunctionArguments

Microsoft.Extensions.AI.GeneratedEmbeddings<TEmbedding>

Microsoft.Extensions.Configuration.Memory.MemoryConfigurationProvider

Microsoft.Extensions.DependencyInjection.IServiceCollection

More…

Attributes

GuidAttribute ComVisibleAttribute

Examples

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.

using System;
using System.Collections;

// Simple business object.
public class Person
{
 public Person(string fName, string lName)
 {
 this.firstName = fName;
 this.lastName = lName;
 }

 public string firstName;
 public string lastName;
}

// Collection of Person objects. This class
// implements IEnumerable so that it can be used
// with ForEach syntax.
public class People : IEnumerable
{
 private Person[] _people;
 public People(Person[] pArray)
 {
 _people = new Person[pArray.Length];

 for (int i = 0; i < pArray.Length; i++)
 {
 _people[i] = pArray[i];
 }
 }

// Implementation for the GetEnumerator method.
 IEnumerator IEnumerable.GetEnumerator()
 {
 return (IEnumerator) GetEnumerator();
 }

 public PeopleEnum GetEnumerator()
 {
 return new PeopleEnum(_people);
 }
}

// When you implement IEnumerable, you must also implement IEnumerator.
public class PeopleEnum : IEnumerator
{
 public Person[] _people;

 // Enumerators are positioned before the first element
 // until the first MoveNext() call.
 int position = -1;

 public PeopleEnum(Person[] list)
 {
 _people = list;
 }

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

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

 object IEnumerator.Current
 {
 get
 {
 return Current;
 }
 }

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

class App
{
 static void Main()
 {
 Person[] peopleArray = new Person[3]
 {
 new Person("John", "Smith"),
 new Person("Jim", "Johnson"),
 new Person("Sue", "Rabon"),
 };

 People peopleList = new People(peopleArray);
 foreach (Person p in peopleList)
 Console.WriteLine(p.firstName + " " + p.lastName);
 }
}

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

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

Remarks

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.

See also

• IEnumerator
• IEnumerable<T>
• Iterators (C#)
• Iterators (Visual Basic)