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Enumerable.FirstOrDefault(Of TSource) Method (IEnumerable(Of TSource), Func(Of TSource, Boolean))

Returns the first element of the sequence that satisfies a condition or a default value if no such element is found.

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

'Declaration
<ExtensionAttribute> _
Public Shared Function FirstOrDefault(Of TSource) ( _
	source As IEnumerable(Of TSource), _
	predicate As Func(Of TSource, Boolean) _
) As TSource

Type Parameters

TSource

The type of the elements of source.

Parameters

source
Type: System.Collections.Generic.IEnumerable(Of TSource)

An IEnumerable(Of T) to return an element from.

predicate
Type: System.Func(Of TSource, Boolean)

A function to test each element for a condition.

Return Value

Type: TSource
default(TSource) if source is empty or if no element passes the test specified by predicate; otherwise, the first element in source that passes the test specified by predicate.

Usage Note

In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable(Of 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).

ExceptionCondition
ArgumentNullException

source or predicate is Nothing.

The default value for reference and nullable types is Nothing.

The following code example demonstrates how to use FirstOrDefault(Of TSource)(IEnumerable(Of TSource), Func(Of TSource, Boolean)) by passing in a predicate. In the second call to the method, there is no element in the array that satisfies the condition.

        ' Create an array of strings. 
        Dim names() As String = _
            {"Hartono, Tommy", "Adams, Terry", "Andersen, Henriette Thaulow", "Hedlund, Magnus", "Ito, Shu"}

        ' Select the first string in the array whose length is greater than 20. 
        Dim firstLongName As String = _
            names.FirstOrDefault(Function(name) name.Length > 20)

        ' Display the output.
        MsgBox("The first long name is " & firstLongName)

        ' Select the first string in the array whose length is greater than 30, 
        ' or a default value if there are no such strings in the array. 
        Dim firstVeryLongName As String = _
            names.FirstOrDefault(Function(name) name.Length > 30)

        Dim text As String = IIf(String.IsNullOrEmpty(firstVeryLongName), "not a", "a")

        MsgBox("There is " & text & " name longer than 30 characters.")

        ' This code produces the following output: 
        
        ' The first long name is Andersen, Henriette Thaulow 
        
        ' There is not a name longer than 30 characters.

.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

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Portable Class Library

Supported in: Portable Class Library
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