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Enumerable.First<TSource> Method (IEnumerable<TSource>, Func<TSource, Boolean>)

Returns the first element in a sequence that satisfies a specified condition.

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

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.

ExceptionCondition
ArgumentNullException

source or predicate is null.

InvalidOperationException

No element satisfies the condition in predicate.

-or-

The source sequence is empty.

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.

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.


      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
      */



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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