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SortedList.IndexOfKey Method

Returns the zero-based index of the specified key in a SortedList object.

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

Public Overridable Function IndexOfKey ( _
	key As Object _
) As Integer


Type: System.Object

The key to locate in the SortedList object.

Return Value

Type: System.Int32
The zero-based index of the key parameter, if key is found in the SortedList object; otherwise, -1.


key is Nothing.


The comparer throws an exception.

The elements of a SortedList object are sorted by the keys either according to a specific IComparer implementation specified when the SortedList is created, or according to the IComparable implementation provided by the keys themselves.

The index sequence is based on the sort sequence. When an element is added, it is inserted into SortedList in the correct sort order, and the indexing adjusts accordingly. When an element is removed, the indexing also adjusts accordingly. Therefore, the index of a specific key/value pair might change as elements are added or removed from the SortedList.

This method uses a binary search algorithm; therefore, this method is an O(log n) operation, where n is Count.

Starting with the .NET Framework 2.0, this method uses the collection’s objects’ Equals and CompareTo methods on item to determine whether item exists. In the earlier versions of the .NET Framework, this determination was made by using the Equals and CompareTo methods of the item parameter on the objects in the collection.

The following code example shows how to determine the index of a key or a value in a SortedList object.

Imports System
Imports System.Collections
Imports Microsoft.VisualBasic

Public Class SamplesSortedList    

    Public Shared Sub Main()

        ' Creates and initializes a new SortedList. 
        Dim mySL As New SortedList()
        mySL.Add(1, "one")
        mySL.Add(3, "three")
        mySL.Add(2, "two")
        mySL.Add(4, "four")
        mySL.Add(0, "zero")

        ' Displays the values of the SortedList.
        Console.WriteLine("The SortedList contains the " & _
           "following values:")

        ' Searches for a specific key. 
        Dim myKey As Integer = 2
        Console.WriteLine("The key ""{0}"" is at index {1}.", myKey, _

        ' Searches for a specific value. 
        Dim myValue As String = "three"
        Console.WriteLine("The value ""{0}"" is at index {1}.", myValue, _
    End Sub     

    Public Shared Sub PrintIndexAndKeysAndValues(myList As SortedList)
        Console.WriteLine(ControlChars.Tab & "-INDEX-" & ControlChars.Tab & _
           "-KEY-" & ControlChars.Tab & "-VALUE-")
        Dim i As Integer 
        For i = 0 To myList.Count - 1
            Console.WriteLine(ControlChars.Tab & "[{0}]:" & ControlChars.Tab & _
               "{1}" & ControlChars.Tab & "{2}", i, myList.GetKey(i), _
        Next i
    End Sub 
End Class 

' This code produces the following output. 
' The SortedList contains the following values: 
'     -INDEX-    -KEY-    -VALUE- 
'     [0]:    0    zero 
'     [1]:    1    one 
'     [2]:    2    two 
'     [3]:    3    three 
'     [4]:    4    four 

' The key "2" is at index 2. 
' The value "three" is at index 3.

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, 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.

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