Enumerable.First<TSource> Method (IEnumerable<TSource>, Func<TSource, Boolean>)
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Returns the first element in a sequence that satisfies a specified condition.
Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
Syntax
'Declaration
<ExtensionAttribute> _
Public Shared Function First(Of TSource) ( _
source As IEnumerable(Of TSource), _
predicate As Func(Of TSource, Boolean) _
) As TSource
public static TSource First<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 an element from.
- predicate
Type: System.Func<TSource, Boolean>
A function to test each element for a condition.
Return Value
Type: TSource
The first element in the sequence that passes the test in the specified predicate function.
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). |
| InvalidOperationException | No element satisfies the condition in predicate. -or- The source sequence is empty. |
Remarks
The First<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>) method throws an exception if no matching element is found in source. To instead return a default value when no matching element is found, use the FirstOrDefault method.
Examples
The following code example demonstrates how to use First<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>) to return the first element of an array that satisfies a condition.
' Create an array of integers.
Dim numbers() As Integer = _
{9, 34, 65, 92, 87, 435, 3, 54, 83, 23, 87, 435, 67, 12, 19}
' Select the first element in the array whose value is greater than 80.
Dim first As Integer = numbers.First(Function(number) number > 80)
' Display the output.
outputBlock.Text &= first & vbCrLf
' This code produces the following output:
'
' 92
int[] numbers = { 9, 34, 65, 92, 87, 435, 3, 54,
83, 23, 87, 435, 67, 12, 19 };
int first = numbers.First(number => number > 80);
outputBlock.Text += first + "\n";
/*
This code produces the following output:
92
*/
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.