Enumerable.FirstOrDefault(Of TSource) Method (IEnumerable(Of TSource), Func(Of TSource, Boolean))
Silverlight
Returns the first element of the sequence that satisfies a condition or a default value if no such element is found.
Namespace: System.Linq
Assembly: 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: TSourcedefault(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.| Exception | Condition |
|---|---|
| ArgumentNullException | source or predicate 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.
outputBlock.Text &= "The first long name is " & firstLongName & vbCrLf
' 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")
outputBlock.Text &= "There is " & text & " name longer than 30 characters." & vbCrLf
' This code produces the following output:
'
' The first long name is Andersen, Henriette Thaulow
'
' There is not a name longer than 30 characters.
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.
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