Articolo
11/18/2011

Queryable.ElementAt<TSource> Method

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

Returns the element at a specified index in a sequence.

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

Syntax

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

public static TSource ElementAt<TSource>(
    this IQueryable<TSource> source,
    int index
)

Type Parameters

TSource
The type of the elements of source.

Parameters

source
Type: System.Linq.IQueryable<TSource>
An IQueryable<T> to return an element from.

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

Return Value

Type: TSource
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).
ArgumentOutOfRangeException	index is less than zero.

Remarks

The ElementAt<TSource>(IQueryable<TSource>, Int32) method generates a MethodCallExpression that represents calling ElementAt<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 ElementAt<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.

Examples

The following code example demonstrates how to use ElementAt<TSource>(IQueryable<TSource>, Int32) to return an element at a specific position in a sequence.

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

      Dim rand As New Random(DateTime.Now.Millisecond)

      Dim name As String = _
          names.AsQueryable().ElementAt(rand.Next(0, names.Length))

      outputBlock.Text &= String.Format("The name chosen at random is '{0}'.", _
                                        name) & vbCrLf

      ' This code produces the following sample output.
      ' Yours may be different due to the use of Random.
      '
      ' The name chosen at random is 'Ito, Shu'.

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

         Random random = new Random(DateTime.Now.Millisecond);

         string name =
             names.AsQueryable().ElementAt(random.Next(0, names.Length));

         outputBlock.Text += String.Format("The name chosen at random is '{0}'.", name) + "\n";

         /*
             This code produces the following sample output.
             Yours may be different due to the use of Random.

             The name chosen at random is 'Ito, Shu'.
         */

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.

Condividi tramite