Enumerable.SingleOrDefault<TSource> Method (IEnumerable<TSource>, Func<TSource, Boolean>)
Microsoft Silverlight will reach end of support after October 2021. Learn more.
Returns the only element of a sequence that satisfies a specified condition or a default value if no such element exists; this method throws an exception if more than one element satisfies the condition.
Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
Syntax
'Declaration
<ExtensionAttribute> _
Public Shared Function SingleOrDefault(Of TSource) ( _
source As IEnumerable(Of TSource), _
predicate As Func(Of TSource, Boolean) _
) As TSource
public static TSource SingleOrDefault<TSource>(
this IEnumerable<TSource> source,
Func<TSource, bool> predicate
)
Type Parameters
- TSource
The type of the elements of source.
Parameters
- source
Type: System.Collections.Generic.IEnumerable<TSource>
An IEnumerable<T> to return a single element from.
- predicate
Type: System.Func<TSource, Boolean>
A function to test an element for a condition.
Return Value
Type: TSource
The single element of the input sequence that satisfies the condition, or default(TSource) if no such element is found.
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.
Exceptions
| Exception | Condition |
|---|---|
| ArgumentNullException | source or predicate is nulla null reference (Nothing in Visual Basic). |
Remarks
The default value for reference and nullable types is nulla null reference (Nothing in Visual Basic).
Examples
The following code example demonstrates how to use SingleOrDefault<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>) to select the only element of an array that satisfies a condition.
' Create an array of strings.
Dim fruits() As String = _
{"apple", "banana", "mango", "orange", "passionfruit", "grape"}
' Get the single item in the array whose length is > 10.
Dim fruit1 As String = _
fruits.SingleOrDefault(Function(fruit) fruit.Length > 10)
' Display the result.
outputBlock.Text &= "First array: " & fruit1 & vbCrLf
string[] fruits = { "apple", "banana", "mango",
"orange", "passionfruit", "grape" };
string fruit1 = fruits.SingleOrDefault(fruit => fruit.Length > 10);
outputBlock.Text += fruit1 + "\n";
/*
This code produces the following output:
passionfruit
*/
The following code example demonstrates that SingleOrDefault<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>) returns a default value when the sequence does not contain exactly one element that satisfies the condition.
' Get the single item in the array whose length is > 15.
Dim fruit2 As String = _
fruits.SingleOrDefault(Function(fruit) fruit.Length > 15)
' Display the result.
Dim output As String = _
IIf(String.IsNullOrEmpty(fruit2), "No single item found", fruit2)
outputBlock.Text &= "Second array: " & output & vbCrLf
' This code produces the following output:
'
' First array: passionfruit
' Second array: No single item found
string fruit2 =
fruits.SingleOrDefault(fruit => fruit.Length > 15);
outputBlock.Text +=
String.IsNullOrEmpty(fruit2) ? "No such string!" : fruit2 + "\n";
/*
This code produces the following output:
No such string!
*/
Version Information
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
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.