• Articolo

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

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Returns the last element of a 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)

Syntax

'Declaration
<ExtensionAttribute> _
Public Shared Function LastOrDefault(Of TSource) ( _
    source As IEnumerable(Of TSource), _
    predicate As Func(Of TSource, Boolean) _
) As TSource

public static TSource LastOrDefault<TSource>(
    this IEnumerable<TSource> source,
    Func<TSource, bool> predicate
)

Type Parameters

  • TSource
    The type of the elements of source.

Parameters

  • predicate
    Type: System.Func<TSource, Boolean>
    A function to test each element for a condition.

Return Value

Type: TSource
default (TSource) if the sequence is empty or if no elements pass the test in the predicate function; otherwise, the last element that passes the test in the 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.

Exceptions

Exception Condition
ArgumentNullException

source or predicate is nulla null reference (Nothing in Visual Basic).

Remarks

The default value for reference and nullable types is nulla null reference (Nothing in Visual Basic).

Examples

The following code example demonstrates how to use LastOrDefault<TSource>(IEnumerable<TSource>, Func<TSource, Boolean>) by passing in a predicate. In the second call to the method, there is no element in the sequence that satisfies the condition.

      ' Create an array of doubles.
      Dim numbers() As Double = {49.6, 52.3, 51.0, 49.4, 50.2, 48.3}

      ' Get the last item whose value rounds to 50.0.
      Dim number50 As Double = _
          numbers.LastOrDefault(Function(n) Math.Round(n) = 50.0)

      Dim output As New System.Text.StringBuilder
      output.AppendLine("The last number that rounds to 50 is " & number50)

      ' Get the last item whose value rounds to 40.0.
      Dim number40 As Double = _
          numbers.LastOrDefault(Function(n) Math.Round(n) = 40.0)

      Dim text As String = IIf(number40 = 0.0, _
                               "[DOES NOT EXIST]", _
                               number40.ToString())
      output.AppendLine("The last number that rounds to 40 is " & text)

      ' Display the output.
      outputBlock.Text &= output.ToString() & vbCrLf

      ' This code produces the following output:
      '
      ' The last number that rounds to 50 is 50.2
      ' The last number that rounds to 40 is [DOES NOT EXIST]


      double[] numbers = { 49.6, 52.3, 51.0, 49.4, 50.2, 48.3 };

      double last50 = numbers.LastOrDefault(n => Math.Round(n) == 50.0);

      outputBlock.Text += String.Format("The last number that rounds to 50 is {0}.", last50) + "\n";

      double last40 = numbers.LastOrDefault(n => Math.Round(n) == 40.0);

      outputBlock.Text += String.Format(
          "The last number that rounds to 40 is {0}.",
          last40 == 0.0 ? "<DOES NOT EXIST>" : last40.ToString()) + "\n";

      /*
       This code produces the following output:

       The last number that rounds to 50 is 50.2.
       The last number that rounds to 40 is <DOES NOT EXIST>.
      */

Version Information

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

Platforms

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