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)
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: TSourceThe 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. For more information, see Extension Methods (Visual Basic) or Extension Methods (C# Programming Guide).| Exception | Condition |
|---|---|
| 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.
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)
{
Console.WriteLine("The collection does not contain exactly one element.");
}
Console.WriteLine(fruit2);
/*
This code produces the following output:
The collection does not contain exactly one element.
*/
Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
