Enumerable.LastOrDefault<(Of <(TSource>)>) Method (IEnumerable<(Of <(TSource>)>))
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Returns the last element of a sequence, or a default value if the sequence contains no elements.
Namespace: System.Linq
Assembly: System.Core (in System.Core.dll)
Syntax
<ExtensionAttribute> _
Public Shared Function LastOrDefault(Of TSource) ( _
source As IEnumerable(Of TSource) _
) As TSource
public static TSource LastOrDefault<TSource>(
this IEnumerable<TSource> source
)
Type Parameters
- TSource
The type of the elements of source.
Parameters
- source
Type: System.Collections.Generic..::.IEnumerable<(Of <(TSource>)>)
An IEnumerable<(Of <(T>)>) to return the last element of.
Return Value
Type: TSource
default(TSource) if the source sequence is empty; otherwise, the last element in the IEnumerable<(Of <(T>)>).
Usage Note
In Visual Basic and C#, you can call this method as an instance method on any object of type IEnumerable<(Of <(TSource>)>). When you use instance method syntax to call this method, omit the first parameter.
Exceptions
| Exception | Condition |
|---|---|
| ArgumentNullException | source is nullNothingnullptra null reference (Nothing in Visual Basic). |
Remarks
The default value for reference and nullable types is nullNothingnullptra null reference (Nothing in Visual Basic).
The Enumerable.LastOrDefault method does not provide a way to specify a default value. If you want to specify a default value other than default(TSource), use the DefaultIfEmpty<(Of <(TSource>)>)(IEnumerable<(Of <(TSource>)>), TSource) method as described in the Example section.
Examples
The following code example demonstrates how to use LastOrDefault<(Of <(TSource>)>)(IEnumerable<(Of <(TSource>)>)) on an empty array.
' Create an empty array.
Dim fruits() As String = {}
' Get the last item in the array, or a
' default value if there are no items.
Dim last As String = fruits.LastOrDefault()
' Display the result.
outputBlock.Text &= IIf(String.IsNullOrEmpty(last), _
"<string is Nothing or empty>", _
last) & vbCrLf
' This code produces the following output:
'
' <string is Nothing or empty>
string[] fruits = { };
string last = fruits.LastOrDefault();
outputBlock.Text +=
String.IsNullOrEmpty(last) ? "<string is null or empty>" : last + "\n";
/*
This code produces the following output:
<string is null or empty>
*/
Sometimes the value of default(TSource) is not the default value that you want to use if the collection contains no elements. Instead of checking the result for the unwanted default value and then changing it if necessary, you can use the DefaultIfEmpty<(Of <(TSource>)>)(IEnumerable<(Of <(TSource>)>), TSource) method to specify the default value that you want to use if the collection is empty. Then, call Last<(Of <(TSource>)>)(IEnumerable<(Of <(TSource>)>)) to obtain the last element. The following code example uses both techniques to obtain a default value of 1 if a collection of numeric days of the month is empty. Because the default value for an integer is 0, which does not correspond to any day of the month, the default value must be specified as 1 instead. The first result variable is checked for the unwanted default value after the query has finished executing. The second result variable is obtained by using DefaultIfEmpty<(Of <(TSource>)>)(IEnumerable<(Of <(TSource>)>), TSource) to specify a default value of 1.
Dim daysOfMonth As New List(Of Integer)(New Integer() {})
' Setting the default value to 1 after the query.
Dim lastDay1 As Integer = daysOfMonth.LastOrDefault()
If lastDay1 = 0 Then
lastDay1 = 1
End If
outputBlock.Text &= String.Format("The value of the lastDay1 variable is {0}", lastDay1) & _
vbCrLf
' Setting the default value to 1 by using DefaultIfEmpty() in the query.
Dim lastDay2 As Integer = daysOfMonth.DefaultIfEmpty(1).Last()
outputBlock.Text &= String.Format("The value of the lastDay2 variable is {0}", lastDay2) & _
vbCrLf
' This code produces the following output:
'
' The value of the lastDay1 variable is 1
' The value of the lastDay2 variable is 1
List<int> daysOfMonth = new List<int> { };
// Setting the default value to 1 after the query.
int lastDay1 = daysOfMonth.LastOrDefault();
if (lastDay1 == 0)
{
lastDay1 = 1;
}
outputBlock.Text += String.Format("The value of the lastDay1 variable is {0}", lastDay1) + "\n";
// Setting the default value to 1 by using DefaultIfEmpty() in the query.
int lastDay2 = daysOfMonth.DefaultIfEmpty(1).Last();
outputBlock.Text += String.Format("The value of the lastDay2 variable is {0}", lastDay2) + "\n";
/*
This code produces the following output:
The value of the lastDay1 variable is 1
The value of the lastDay2 variable is 1
*/
Version Information
Windows Phone OS
Supported in: 8.1, 8.0, 7.1, 7.0
Platforms
Windows Phone