Queryable.ElementAtOrDefault<TSource> Method

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 IQueryable(Of TSource), _
    index As Integer _
) As TSource
public static TSource ElementAtOrDefault<TSource>(
    this IQueryable<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 index is outside the bounds of source; otherwise, the element at the specified position in source.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IQueryable<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

The ElementAtOrDefault<TSource>(IQueryable<TSource>, Int32) method generates a MethodCallExpression that represents calling ElementAtOrDefault<TSource>(IQueryable<TSource>, Int32) itself as a constructed generic method. It then passes the MethodCallExpression to the Execute<TResult>(Expression) method of the IQueryProvider represented by the Provider property of the source parameter.

The query behavior that occurs as a result of executing an expression tree that represents calling ElementAtOrDefault<TSource>(IQueryable<TSource>, Int32) depends on the implementation of the type of the source parameter. The expected behavior is that it returns the item at position index in source, or default(TSource) if index is outside the bounds of source.

Examples

The following code example demonstrates how to use ElementAtOrDefault<TSource>(IQueryable<TSource>, Int32). This example uses a value for index that is outside the bounds of the source sequence.

      Dim names() As String = {"Hartono, Tommy", "Adams, Terry", _
                         "Andersen, Henriette Thaulow", _
                         "Hedlund, Magnus", "Ito, Shu"}

      Dim index As Integer = 20

      Dim name As String = names.AsQueryable().ElementAtOrDefault(index)

      outputBlock.Text &= String.Format("The name at index {0} is '{1}'.", _
          index, IIf(String.IsNullOrEmpty(name), "[NONE AT THIS INDEX]", name)) & vbCrLf

      ' This code produces the following output:
      '
      ' The name at index 20 is '[NONE AT THIS INDEX]'.

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

         int index = 20;

         string name = names.AsQueryable().ElementAtOrDefault(index);

         outputBlock.Text += String.Format(
             "The name chosen at index {0} is '{1}'.",
             index,
             String.IsNullOrEmpty(name) ? "[NONE AT THIS INDEX]" : name) + "\n";

         /*
             This code produces the following output:

             The name chosen at index 20 is '[NONE AT THIS INDEX]'.
         */

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1

Platforms

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