Artigo
11/18/2011

IEnumerator.Current Property

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Gets the current element in the collection.

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

Syntax

'Declaration
ReadOnly Property Current As Object

Object Current { get; }

Property Value

Type: System.Object
The current element in the collection.

Exceptions

Exception	Condition
InvalidOperationException	The enumerator is positioned before the first element of the collection or after the last element. -or- The collection was modified after the enumerator was created.

InvalidOperationException

The enumerator is positioned before the first element of the collection or after the last element.

-or-

The collection was modified after the enumerator was created.

Remarks

After an enumerator is created or after the Reset method is called, the MoveNext method must be called to advance the enumerator to the first element of the collection before reading the value of the Current property; otherwise, Current is undefined.

Current also throws an exception if the last call to MoveNext returned false, which indicates the end of the collection.

Current does not move the position of the enumerator, and consecutive calls to Current return the same object until either MoveNext or Reset is called.

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. If the collection is modified between MoveNext and Current, Current returns the element that it is set to, even if the enumerator is already invalidated.

Examples

The following code example demonstrates the implementation of the IEnumerator interfaces for a custom collection. In this example, Current 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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