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.
Assembly: System.Core (in System.Core.dll)
public static TSource FirstOrDefault<TSource>( this IEnumerable<TSource> source, Func<TSource, bool> predicate )
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: 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.
Type Parameters
- TSource
The type of the elements of source.
| Exception | Condition |
|---|---|
| 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. */
Available since 8
.NET Framework
Available since 3.5
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1