ArrayList.GetEnumerator Method (Int32, Int32)


Returns an enumerator for a range of elements in the ArrayList.

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

Public Overridable Function GetEnumerator (
	index As Integer,
	count As Integer
) As IEnumerator


Type: System.Int32

The zero-based starting index of the ArrayList section that the enumerator should refer to.

Type: System.Int32

The number of elements in the ArrayList section that the enumerator should refer to.

Return Value

Type: System.Collections.IEnumerator

An IEnumerator for the specified range of elements in the ArrayList.

Exception Condition

index is less than zero.


count is less than zero.


index and count do not specify a valid range in the ArrayList.

The foreach statement of the C# language (for each in Visual C++, For Each 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. Reset also brings the enumerator back to this position. 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 either MoveNext or Reset 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. To set Current to the first element of the collection again, you can call Reset followed by MoveNext.

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 its behavior is undefined.

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.

This method is an O(1) operation.

In the .NET Framework versions 1.0 and 1.1, the enumerator for an ArrayList wrapper returned by the Adapter method treated the second argument as an upper bound rather than as a count. In the .NET Framework 2.0 the second argument is correctly treated as a count.

The following example gets the enumerator for an ArrayList, and the enumerator for a range of elements in the ArrayList.

Imports System
Imports System.Collections

Class Program
    Private Shared Sub Main(ByVal args As String())
        Dim colors As New ArrayList()

        Dim e As IEnumerator = colors.GetEnumerator()
        While e.MoveNext()
            Dim obj As [Object] = e.Current
        End While


        Dim e2 As IEnumerator = colors.GetEnumerator(2, 4)
        While e2.MoveNext()
            Dim obj As [Object] = e2.Current
        End While
    End Sub
End Class

' This code example produces
' the following ouput:
' red
' blue
' green
' yellow
' beige
' brown
' magenta
' purple
' green
' yellow
' beige
' brown

Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
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