Enumerable.FirstOrDefault<TSource> Method (IEnumerable<TSource>, Func<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)

public static TSource FirstOrDefault<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
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<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 null.

The default value for reference and nullable types is null.

The following code example demonstrates how to use FirstOrDefault<TSource>(IEnumerable<TSource>, Func<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.

            string[] names = { "Hartono, Tommy", "Adams, Terry", 
                                 "Andersen, Henriette Thaulow", 
                                 "Hedlund, Magnus", "Ito, Shu" };

            string firstLongName = names.FirstOrDefault(name => name.Length > 20);

            Console.WriteLine("The first long name is '{0}'.", firstLongName);

            string firstVeryLongName = names.FirstOrDefault(name => name.Length > 30);

            Console.WriteLine(
                "There is {0} name longer than 30 characters.",
                string.IsNullOrEmpty(firstVeryLongName) ? "not a" : "a");

            /*
             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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