IEnumerator(T) Interface
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IEnumerator<T> Interface


Supports a simple iteration over a generic collection.

Namespace:   System.Collections.Generic
Assembly:  mscorlib (in mscorlib.dll)

public interface IEnumerator<out T> : IDisposable, IEnumerator

Type Parameters

out T

The type of objects to enumerate.


Gets the element in the collection at the current position of the enumerator.


Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.(Inherited from IDisposable.)


Advances the enumerator to the next element of the collection.(Inherited from IEnumerator.)


Sets the enumerator to its initial position, which is before the first element in the collection.(Inherited from IEnumerator.)

IEnumerator<T> is the base interface for all generic enumerators.

The foreach statement of the C# language (for each in C++, For Each in Visual Basic) hides the complexity of the enumerators. Therefore, using foreach is recommended, instead of directly manipulating the enumerator.

Enumerators can be used to read the data in the collection, but they cannot be used to modify the underlying collection.

Initially, the enumerator is positioned before the first element in the collection. At this position, Current is undefined. Therefore, you must call MoveNext to advance the enumerator to the first element of the collection before reading the value of Current.

Current returns the same object until MoveNext is called. MoveNext sets Current to the next element.

If MoveNext passes the end of the collection, the enumerator is positioned after the last element in the collection and MoveNext returns false. When the enumerator is at this position, subsequent calls to MoveNext also return false. If the last call to MoveNext returned false, Current is undefined. You cannot set Current to the first element of the collection again; you must create a new enumerator instance instead.

The Reset method is provided for COM interoperability. It does not necessarily need to be implemented; instead, the implementer can simply throw a NotSupportedException. However, if you choose to do this, you should make sure no callers are relying on the Reset functionality.

An enumerator remains valid as long as the collection remains unchanged. If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is irrecoverably invalidated and the next call to MoveNext or Reset throws an InvalidOperationException.

The enumerator does not have exclusive access to the collection; therefore, enumerating through a collection is intrinsically not a thread-safe procedure. To guarantee thread safety during enumeration, you can lock the collection during the entire enumeration. To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization.

Default implementations of collections in the System.Collections.Generic namespace are not synchronized.

Notes to Implementers:

Implementing this interface requires implementing the nongeneric IEnumerator interface. The MoveNext and Resetmethods do not depend on T, and appear only on the nongeneric interface. The Current property appears on both interfaces, and has different return types. Implement the nongeneric IEnumerator.Current property as an explicit interface implementation. This allows any consumer of the nongeneric interface to consume the generic interface.

In addition, IEnumerator<T> implements IDisposable, which requires you to implement the Dispose method. This enables you to close database connections or release file handles or similar operations when using other resources. If there are no additional resources to dispose of, provide an empty Dispose implementation.

The following example shows an implementation of the IEnumerator<T> interface for a collection class of custom objects. The custom object is an instance of the type Box, and the collection class is BoxCollection. This code example is part of a larger example provided for the ICollection<T> interface.

// Defines the enumerator for the Boxes collection.
// (Some prefer this class nested in the collection class.)
public class BoxEnumerator : IEnumerator<Box>
    private BoxCollection _collection;
    private int curIndex;
    private Box curBox;

    public BoxEnumerator(BoxCollection collection)
        _collection = collection;
        curIndex = -1;
        curBox = default(Box);


    public bool MoveNext()
        //Avoids going beyond the end of the collection.
        if (++curIndex >= _collection.Count)
            return false;
            // Set current box to next item in collection.
            curBox = _collection[curIndex];
        return true;

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

    void IDisposable.Dispose() { }

    public Box Current
        get { return curBox; }

    object IEnumerator.Current
        get { return Current; }


Universal Windows Platform
Available since 4.5
.NET Framework
Available since 2.0
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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