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: 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.
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).| Exception | Condition |
|---|---|
| ArgumentNullException | source or predicate 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.
*/
Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
