• Article

List<T>.LastIndexOf Method (T, Int32, Int32)

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Searches for the specified object and returns the zero-based index of the last occurrence within the range of elements in the List<T> that contains the specified number of elements and ends at the specified index.

Namespace:  System.Collections.Generic
Assembly:  mscorlib (in mscorlib.dll)

Syntax

'Declaration
Public Function LastIndexOf ( _
    item As T, _
    index As Integer, _
    count As Integer _
) As Integer

public int LastIndexOf(
    T item,
    int index,
    int count
)

Parameters

  • item
    Type: T
    The object to locate in the List<T>. The value can be nulla null reference (Nothing in Visual Basic) for reference types.
  • index
    Type: System.Int32
    The zero-based starting index of the backward search.
  • count
    Type: System.Int32
    The number of elements in the section to search.

Return Value

Type: System.Int32
The zero-based index of the last occurrence of item within the range of elements in the List<T> that contains count number of elements and ends at index, if found; otherwise, –1.

Exceptions

Exception Condition
ArgumentOutOfRangeException

index is outside the range of valid indexes for the List<T>.

-or-

count is less than 0.

-or-

index and count do not specify a valid section in the List<T>.

Remarks

The List<T> is searched backward starting at index and ending at index minus count plus 1, if count is greater than 0.

This method determines equality using the default equality comparer EqualityComparer<T>.Default for T, the type of values in the list.

This method performs a linear search; therefore, this method is an O(n) operation, where n is count.

Examples

The following code example demonstrates all three overloads of the LastIndexOf method. A List<T> of strings is created, with one entry that appears twice, at index location 0 and index location 5. The LastIndexOf(T) method overload searches the entire list from the end, and finds the second occurrence of the string. The LastIndexOf(T, Int32) method overload is used to search the list backward beginning with index location 3 and continuing to the beginning of the list, so it finds the first occurrence of the string in the list. Finally, the LastIndexOf(T, Int32, Int32) method overload is used to search a range of 4 entries, beginning at index location 4 and extending backward (that is, it searches the items at locations 4, 3, 2, and 1); this search returns –1 because there are no instances of the search string in that range.

Imports System.Collections.Generic

Public Class Example

   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)

      Dim dinosaurs As New List(Of String)

      dinosaurs.Add("Tyrannosaurus")
      dinosaurs.Add("Amargasaurus")
      dinosaurs.Add("Mamenchisaurus")
      dinosaurs.Add("Brachiosaurus")
      dinosaurs.Add("Deinonychus")
      dinosaurs.Add("Tyrannosaurus")
      dinosaurs.Add("Compsognathus")

      outputBlock.Text &= vbCrLf
      For Each dinosaur As String In dinosaurs
         outputBlock.Text &= dinosaur & vbCrLf
      Next

      outputBlock.Text &= String.Format(vbLf & _
          "LastIndexOf(""Tyrannosaurus""): {0}", _
          dinosaurs.LastIndexOf("Tyrannosaurus")) & vbCrLf

      outputBlock.Text &= String.Format(vbLf & _
          "LastIndexOf(""Tyrannosaurus"", 3): {0}", _
          dinosaurs.LastIndexOf("Tyrannosaurus", 3)) & vbCrLf

      outputBlock.Text &= String.Format(vbLf & _
          "LastIndexOf(""Tyrannosaurus"", 4, 4): {0}", _
          dinosaurs.LastIndexOf("Tyrannosaurus", 4, 4)) & vbCrLf

   End Sub
End Class

' This code example produces the following output:
'
'Tyrannosaurus
'Amargasaurus
'Mamenchisaurus
'Brachiosaurus
'Deinonychus
'Tyrannosaurus
'Compsognathus
'
'LastIndexOf("Tyrannosaurus"): 5
'
'LastIndexOf("Tyrannosaurus", 3): 0
'
'LastIndexOf("Tyrannosaurus", 4, 4): -1

using System;
using System.Collections.Generic;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      List<string> dinosaurs = new List<string>();

      dinosaurs.Add("Tyrannosaurus");
      dinosaurs.Add("Amargasaurus");
      dinosaurs.Add("Mamenchisaurus");
      dinosaurs.Add("Brachiosaurus");
      dinosaurs.Add("Deinonychus");
      dinosaurs.Add("Tyrannosaurus");
      dinosaurs.Add("Compsognathus");

      outputBlock.Text += "\n";
      foreach (string dinosaur in dinosaurs)
      {
         outputBlock.Text += dinosaur + "\n";
      }

      outputBlock.Text += String.Format("\nLastIndexOf(\"Tyrannosaurus\"): {0}",
          dinosaurs.LastIndexOf("Tyrannosaurus")) + "\n";

      outputBlock.Text += String.Format("\nLastIndexOf(\"Tyrannosaurus\", 3): {0}",
          dinosaurs.LastIndexOf("Tyrannosaurus", 3)) + "\n";

      outputBlock.Text += String.Format("\nLastIndexOf(\"Tyrannosaurus\", 4, 4): {0}",
          dinosaurs.LastIndexOf("Tyrannosaurus", 4, 4)) + "\n";
   }
}

/* This code example produces the following output:

Tyrannosaurus
Amargasaurus
Mamenchisaurus
Brachiosaurus
Deinonychus
Tyrannosaurus
Compsognathus

LastIndexOf("Tyrannosaurus"): 5

LastIndexOf("Tyrannosaurus", 3): 0

LastIndexOf("Tyrannosaurus", 4, 4): -1
 */

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.