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Enumerable.Single<TSource> Method (IEnumerable<TSource>)

Returns the only element of a sequence, and throws an exception if there is not exactly one element in the sequence.

Namespace:  System.Linq
Assembly:  System.Core (in System.Core.dll)
public static TSource Single<TSource>(
	this IEnumerable<TSource> source
)

Type Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Collections.Generic.IEnumerable<TSource>
An IEnumerable<T> to return the single element of.

Return Value

Type: TSource
The single element of the input 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.
ExceptionCondition
ArgumentNullException

source is null.

InvalidOperationException

The input sequence contains more than one element.

-or-

The input sequence is empty.

The Single<TSource>(IEnumerable<TSource>) method throws an exception if the input sequence is empty. To instead return null when the input sequence is empty, use SingleOrDefault.

The following code example demonstrates how to use Single<TSource>(IEnumerable<TSource>) to select the only element of an array.


      string[] fruits1 = { "orange" };

      string fruit1 = fruits1.Single();

      outputBlock.Text += fruit1 + "\n";

      /*
       This code produces the following output:

       orange
      */



The following code example demonstrates that Single<TSource>(IEnumerable<TSource>) throws an exception when the sequence does not contain exactly one element.


      string[] fruits2 = { "orange", "apple" };
      string fruit2 = null;

      try
      {
         fruit2 = fruits2.Single();
      }
      catch (System.InvalidOperationException)
      {
         outputBlock.Text += "The collection does not contain exactly one element." + "\n";
      }

      outputBlock.Text += fruit2 + "\n";

      /*
       This code produces the following output:

       The collection does not contain exactly one element.
      */



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

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

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