ArrayList.GetEnumerator Method

Definition

Namespace:

System.Collections

Assembly:

System.Runtime.dll

Returns an enumerator that iterates through the ArrayList.

Overloads

GetEnumerator()	Returns an enumerator for the entire ArrayList.
GetEnumerator(Int32, Int32)	Returns an enumerator for a range of elements in the ArrayList.

GetEnumerator()

Source:

ArrayList.cs

Returns an enumerator for the entire ArrayList.

public:
 virtual System::Collections::IEnumerator ^ GetEnumerator();

public virtual System.Collections.IEnumerator GetEnumerator ();

abstract member GetEnumerator : unit -> System.Collections.IEnumerator
override this.GetEnumerator : unit -> System.Collections.IEnumerator

Public Overridable Function GetEnumerator () As IEnumerator

Returns

IEnumerator

An IEnumerator for the entire ArrayList.

Implements

GetEnumerator()

Examples

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

using System;
using System.Collections;

class Program
{
    static void Main(string[] args)
    {
        ArrayList colors = new ArrayList();
        colors.Add("red");
        colors.Add("blue");
        colors.Add("green");
        colors.Add("yellow");
        colors.Add("beige");
        colors.Add("brown");
        colors.Add("magenta");
        colors.Add("purple");

        IEnumerator e = colors.GetEnumerator();
        while (e.MoveNext())
        {
            Object obj = e.Current;
            Console.WriteLine(obj);
        }

        Console.WriteLine();

        IEnumerator e2 = colors.GetEnumerator(2, 4);
        while (e2.MoveNext())
        {
            Object obj = e2.Current;
            Console.WriteLine(obj);
        }
    }
}

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

    green
    yellow
    beige
    brown
 */

Imports System.Collections

Class Program
    Private Shared Sub Main(ByVal args As String())
        Dim colors As New ArrayList()
        colors.Add("red")
        colors.Add("blue")
        colors.Add("green")
        colors.Add("yellow")
        colors.Add("beige")
        colors.Add("brown")
        colors.Add("magenta")
        colors.Add("purple")
        
        Dim e As IEnumerator = colors.GetEnumerator()
        While e.MoveNext()
            Dim obj As [Object] = e.Current
            Console.WriteLine(obj)
        End While
        
        Console.WriteLine()
        
        Dim e2 As IEnumerator = colors.GetEnumerator(2, 4)
        While e2.MoveNext()
            Dim obj As [Object] = e2.Current
            Console.WriteLine(obj)
        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
'

Remarks

The foreach statement of the C# language (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. 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.

See also

• IEnumerator

GetEnumerator(Int32, Int32)

Source:

ArrayList.cs

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

public:
 virtual System::Collections::IEnumerator ^ GetEnumerator(int index, int count);

public virtual System.Collections.IEnumerator GetEnumerator (int index, int count);

abstract member GetEnumerator : int * int -> System.Collections.IEnumerator
override this.GetEnumerator : int * int -> System.Collections.IEnumerator

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

Parameters

index

Int32

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

count

Int32

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

Returns

IEnumerator

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

Exceptions

ArgumentOutOfRangeException

index is less than zero.

-or-

count is less than zero.

ArgumentException

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

Examples

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

using System;
using System.Collections;

class Program
{
    static void Main(string[] args)
    {
        ArrayList colors = new ArrayList();
        colors.Add("red");
        colors.Add("blue");
        colors.Add("green");
        colors.Add("yellow");
        colors.Add("beige");
        colors.Add("brown");
        colors.Add("magenta");
        colors.Add("purple");

        IEnumerator e = colors.GetEnumerator();
        while (e.MoveNext())
        {
            Object obj = e.Current;
            Console.WriteLine(obj);
        }

        Console.WriteLine();

        IEnumerator e2 = colors.GetEnumerator(2, 4);
        while (e2.MoveNext())
        {
            Object obj = e2.Current;
            Console.WriteLine(obj);
        }
    }
}

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

    green
    yellow
    beige
    brown
 */

Imports System.Collections

Class Program
    Private Shared Sub Main(ByVal args As String())
        Dim colors As New ArrayList()
        colors.Add("red")
        colors.Add("blue")
        colors.Add("green")
        colors.Add("yellow")
        colors.Add("beige")
        colors.Add("brown")
        colors.Add("magenta")
        colors.Add("purple")
        
        Dim e As IEnumerator = colors.GetEnumerator()
        While e.MoveNext()
            Dim obj As [Object] = e.Current
            Console.WriteLine(obj)
        End While
        
        Console.WriteLine()
        
        Dim e2 As IEnumerator = colors.GetEnumerator(2, 4)
        While e2.MoveNext()
            Dim obj As [Object] = e2.Current
            Console.WriteLine(obj)
        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
'

Remarks

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.

See also

• IEnumerator