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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
Assembly:  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.

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);

      outputBlock.Text += String.Format("The first long name is '{0}'.", firstLongName) + "\n";

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

      outputBlock.Text += String.Format(
          "There is {0} name longer than 30 characters.",
          string.IsNullOrEmpty(firstVeryLongName) ? "not a" : "a") + "\n";

      /*
       This code produces the following output:

       The first long name is 'Andersen, Henriette Thaulow'.
       There is not a name longer than 30 characters.
      */



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

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

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