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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.

  NameDescription
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsGetEnumeratorReturns an enumerator that iterates through a collection.
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  NameDescription
Public Extension MethodSupported by Portable Class LibrarySupported in .NET for Windows Store appsAsParallelEnables parallelization of a query. (Defined by ParallelEnumerable.)
Public Extension MethodSupported by Portable Class LibrarySupported in .NET for Windows Store appsAsQueryableConverts an IEnumerable to an IQueryable. (Defined by Queryable.)
Public Extension MethodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsCast<TResult>Casts the elements of an IEnumerable to the specified type. (Defined by Enumerable.)
Public Extension MethodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsOfType<TResult>Filters the elements of an IEnumerable based on a specified type. (Defined by Enumerable.)
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NoteNote

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.

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

using System;
using System.Collections;

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

    public string firstName;
    public string lastName;
}

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];
        }
    }

    IEnumerator IEnumerable.GetEnumerator()
    {
       return (IEnumerator) GetEnumerator();
    }

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

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
 *
 */

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

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

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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