Partager via

  • Article

Enumerable.ElementAtOrDefault<TSource> Method

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

Returns the element at a specified index in a sequence or a default value if the index is out of range.

Namespace:  System.Linq
Assembly:  System.Core (in System.Core.dll)

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function ElementAtOrDefault(Of TSource) ( _
    source As IEnumerable(Of TSource), _
    index As Integer _
) As TSource

public static TSource ElementAtOrDefault<TSource>(
    this IEnumerable<TSource> source,
    int index
)

Type Parameters

  • TSource
    The type of the elements of source.

Parameters

  • index
    Type: System.Int32
    The zero-based index of the element to retrieve.

Return Value

Type: TSource
default (TSource) if the index is outside the bounds of the source sequence; otherwise, the element at the specified position in the source sequence.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable<TSource>. When you use instance method syntax to call this method, omit the first parameter.

Exceptions

Exception Condition
ArgumentNullException

source is nulla null reference (Nothing in Visual Basic).

Remarks

If the type of source implements IList<T>, that implementation is used to obtain the element at the specified index. Otherwise, this method obtains the specified element.

The default value for reference and nullable types is nulla null reference (Nothing in Visual Basic).

Examples

The following code example demonstrates how to use ElementAtOrDefault<TSource>. This example uses an index that is outside the bounds of the array.

      ' Create an array of strings.
      Dim names() As String = _
          {"Hartono, Tommy", "Adams, Terry", "Andersen, Henriette Thaulow", "Hedlund, Magnus", "Ito, Shu"}

      Dim index As Integer = 20

      ' Get a string at an index that is out of range in the array.
      Dim name As String = names.ElementAtOrDefault(index)

      Dim text As String = IIf(String.IsNullOrEmpty(name), "[THERE IS NO NAME AT THIS INDEX]", name)

      ' Display the output.
      outputBlock.Text &= "The name chosen at index " & index & " is " & text & vbCrLf

      ' This code produces the following output:
      '
      ' The name chosen at index 20 is [THERE IS NO NAME AT THIS INDEX]


      string[] names =
             { "Hartono, Tommy", "Adams, Terry", "Andersen, Henriette Thaulow",
                 "Hedlund, Magnus", "Ito, Shu" };

      int index = 20;

      string name = names.ElementAtOrDefault(index);

      outputBlock.Text += String.Format(
          "The name chosen at index {0} is '{1}'.",
          index,
          String.IsNullOrEmpty(name) ? "<no name at this index>" : name) + "\n";

      /*
       This code produces the following output:

       The name chosen at index 20 is '<no name at this index>'.
      */

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.