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.NET Framework Class Library
EnumerableSingleOrDefaultTSource Method (IEnumerableTSource, FuncTSource, Boolean)

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
Assemblies:   System.Linq (in System.Linq.dll)
  System.Core (in System.Core.dll)
Syntax
<[%$TOPIC/bb549274_en-us_VS_110_1_0_0_0_0%]> _
Public Shared Function SingleOrDefault(Of TSource) ( _
	source As [%$TOPIC/bb549274_en-us_VS_110_1_0_0_0_1%](Of TSource), _
	predicate As [%$TOPIC/bb549274_en-us_VS_110_1_0_0_0_2%](Of TSource, [%$TOPIC/bb549274_en-us_VS_110_1_0_0_0_3%]) _
) As TSource
public static TSource SingleOrDefault<TSource>(
	this [%$TOPIC/bb549274_en-us_VS_110_1_0_1_0_0%]<TSource> source,
	[%$TOPIC/bb549274_en-us_VS_110_1_0_1_0_1%]<TSource, [%$TOPIC/bb549274_en-us_VS_110_1_0_1_0_2%]> predicate
)
[[%$TOPIC/bb549274_en-us_VS_110_1_0_2_0_0%]]
public:
generic<typename TSource>
static TSource SingleOrDefault(
	[%$TOPIC/bb549274_en-us_VS_110_1_0_2_0_1%]<TSource>^ source, 
	[%$TOPIC/bb549274_en-us_VS_110_1_0_2_0_2%]<TSource, [%$TOPIC/bb549274_en-us_VS_110_1_0_2_0_3%]>^ predicate
)
static member SingleOrDefault : 
        source:[%$TOPIC/bb549274_en-us_VS_110_1_0_3_0_0%]<'TSource> * 
        predicate:[%$TOPIC/bb549274_en-us_VS_110_1_0_3_0_1%]<'TSource, [%$TOPIC/bb549274_en-us_VS_110_1_0_3_0_2%]> -> 'TSource 
JScript does not support generic types or methods.

Type Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Collections.GenericIEnumerableTSource

An IEnumerableT to return a single element from.

predicate
Type: SystemFuncTSource, 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 IEnumerableTSource. 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).
Exceptions
ExceptionCondition
ArgumentNullException

source or predicate is .

Remarks

The default value for reference and nullable types is .

Examples

The following code example demonstrates how to use SingleOrDefaultTSource(IEnumerableTSource, FuncTSource, 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.
MsgBox("First array: " & fruit1)
string[] fruits = { "apple", "banana", "mango", 
                                  "orange", "passionfruit", "grape" };

            string fruit1 = fruits.SingleOrDefault(fruit => fruit.Length > 10);

            Console.WriteLine(fruit1);

            /*
             This code produces the following output:

             passionfruit
            */

The following code example demonstrates that SingleOrDefaultTSource(IEnumerableTSource, FuncTSource, 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)
        MsgBox("Second array: " & output)

        ' This code produces the following output: 
        ' 
        ' First array: passionfruit 
        ' Second array: No single item found
string fruit2 =
                fruits.SingleOrDefault(fruit => fruit.Length > 15);

            Console.WriteLine(
                String.IsNullOrEmpty(fruit2) ? "No such string!" : fruit2);

            /*
             This code produces the following output:

             No such string!
            */
Version Information

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0

Portable Class Library

Supported in: Portable Class Library

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8