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ArrayList.IndexOf Method (Object, Int32)

Searches for the specified Object and returns the zero-based index of the first occurrence within the range of elements in the ArrayList that extends from the specified index to the last element.

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

'Declaration
Public Overridable Function IndexOf ( _
	value As Object, _
	startIndex As Integer _
) As Integer

Parameters

value
Type: System.Object

The Object to locate in the ArrayList. The value can be Nothing.

startIndex
Type: System.Int32

The zero-based starting index of the search. 0 (zero) is valid in an empty list.

Return Value

Type: System.Int32
The zero-based index of the first occurrence of value within the range of elements in the ArrayList that extends from startIndex to the last element, if found; otherwise, -1.

ExceptionCondition
ArgumentOutOfRangeException

startIndex is outside the range of valid indexes for the ArrayList.

The ArrayList is searched forward starting at startIndex and ending at the last element.

This method performs a linear search; therefore, this method is an O(n) operation, where n is the number of elements from startIndex to the end of the ArrayList.

This method determines equality by calling Object.Equals.

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 the first occurrence of a specified element.

Imports System
Imports System.Collections
Imports Microsoft.VisualBasic

Public Class SamplesArrayList


    Public Shared Sub Main()

        ' Creates and initializes a new ArrayList with three elements of the same value. 
        Dim myAL As New ArrayList()
        myAL.Add("the")
        myAL.Add("quick")
        myAL.Add("brown")
        myAL.Add("fox")
        myAL.Add("jumps")
        myAL.Add("over")
        myAL.Add("the")
        myAL.Add("lazy")
        myAL.Add("dog")
        myAL.Add("in")
        myAL.Add("the")
        myAL.Add("barn")

        ' Displays the values of the ArrayList.
        Console.WriteLine("The ArrayList contains the following values:")
        PrintIndexAndValues(myAL)

        ' Search for the first occurrence of the duplicated value. 
        Dim myString As [String] = "the" 
        Dim myIndex As Integer = myAL.IndexOf(myString)
        Console.WriteLine("The first occurrence of ""{0}"" is at index {1}.", myString, myIndex)

        ' Search for the first occurrence of the duplicated value in the last section of the ArrayList.
        myIndex = myAL.IndexOf(myString, 4)
        Console.WriteLine("The first occurrence of ""{0}"" between index 4 and the end is at index {1}.", myString, myIndex)

        ' Search for the first occurrence of the duplicated value in a section of the ArrayList.
        myIndex = myAL.IndexOf(myString, 6, 6)
        Console.WriteLine("The first occurrence of ""{0}"" between index 6 and index 11 is at index {1}.", myString, myIndex)

        ' Search for the first occurrence of the duplicated value in a small section at the end of the ArrayList.
        myIndex = myAL.IndexOf(myString, 11)
        Console.WriteLine("The first occurrence of ""{0}"" between index 11 and the end is at index {1}.", myString, myIndex)

    End Sub 'Main

    Public Shared Sub PrintIndexAndValues(ByVal myList As IEnumerable)
        Dim i As Integer 
        Dim obj As [Object]
        For Each obj In myList
            Console.WriteLine("   [{0}]:    {1}", i, obj)
            i = i + 1
        Next obj
        Console.WriteLine()
    End Sub 'PrintIndexAndValues

End Class 'SamplesArrayList

' This code produces the following output. 

' The ArrayList contains the following values: 
' 	[0]:	the 
' 	[1]:	quick 
' 	[2]:	brown 
' 	[3]:	fox 
' 	[4]:	jumps 
' 	[5]:	over 
' 	[6]:	the 
' 	[7]:	lazy 
' 	[8]:	dog 
' 	[9]:	in 
' 	[10]:	the 
' 	[11]:	barn 
'  
' The first occurrence of "the" is at index 0. 
' The first occurrence of "the" between index 4 and the end is at index 6. 
' The first occurrence of "the" between index 6 and index 11 is at index 6. 
' The first occurrence of "the" between index 11 and the end is at index -1. 
' 

.NET Framework

Supported in: 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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