Article
11/18/2011

IEnumerator.Reset Method

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Sets the enumerator to its initial position, which is before the first element in the collection.

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

Syntax

'Declaration
Sub Reset

void Reset()

Exceptions

Exception	Condition
InvalidOperationException	The collection was modified after the enumerator was created.

Remarks

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 the MoveNext or Reset method throws an InvalidOperationException.

The Reset method is provided for COM interoperability. It does not necessarily need to be implemented; instead, the implementer can simply throw a NotSupportedException.

Notes to Implementers

All calls to Reset must result in the same state for the enumerator. The preferred implementation is to move the enumerator to the beginning of the collection, before the first element. This invalidates the enumerator if the collection has been modified since the enumerator was created, which is consistent with MoveNext and Current.

Examples

The following code example demonstrates the implementation of the IEnumerator interfaces for a custom collection. In this example, Reset is not explicitly called, but it is implemented to support the use of foreach (for each in Visual Basic). This code example is part of a larger example for the IEnumerator interface.

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

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;
   }

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

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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