项目
11/18/2011

Queryable.Reverse<TSource> Method

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Inverts the order of the elements in a sequence.

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

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function Reverse(Of TSource) ( _
    source As IQueryable(Of TSource) _
) As IQueryable(Of TSource)

public static IQueryable<TSource> Reverse<TSource>(
    this IQueryable<TSource> source
)

Type Parameters

TSource
The type of the elements of source.

Parameters

source
Type: System.Linq.IQueryable<TSource>
A sequence of values to reverse.

Return Value

Type: System.Linq.IQueryable<TSource>
An IQueryable<T> whose elements correspond to those of the input sequence in reverse order.

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 Reverse<TSource>(IQueryable<TSource>) method generates a MethodCallExpression that represents calling Reverse<TSource>(IQueryable<TSource>) itself as a constructed generic method. It then passes the MethodCallExpression to the CreateQuery<TElement>(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 Reverse<TSource>(IQueryable<TSource>) depends on the implementation of the type of the source parameter. The expected behavior is that it reverses the order of the elements in source.

Examples

The following code example demonstrates how to use Reverse<TSource>(IQueryable<TSource>) to reverse the order of elements in an array.

      Dim appleLetters As New List(Of Char)(New Char() _
                                            {"a"c, "p"c, "p"c, "l"c, "e"c})

      ' Reverse the order of the characters in the collection.
      Dim reversed As IQueryable(Of Char) = _
         appleLetters.AsQueryable().Reverse()

      Dim output As New System.Text.StringBuilder
      For Each chr As Char In reversed
         output.Append(chr & " ")
      Next

      ' Display the output.
      outputBlock.Text &= output.ToString() & vbCrLf

      ' This code produces the following output:
      '
      ' e l p p a

         char[] apple = { 'a', 'p', 'p', 'l', 'e' };

         // Reverse the order of the characters in the collection.
         IQueryable<char> reversed = apple.AsQueryable().Reverse();

         foreach (char chr in reversed)
            outputBlock.Text += chr + " ";
         outputBlock.Text += "\n";

         /*
             This code produces the following output:

             e l p p a
         */

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.

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