VB.Net Tutorial/Collections/ArrayList

Add different data types to ArrayList

<source lang="vbnet">Imports System.Collections public class AddElementsToArrayLista

  public Shared Sub Main
              Dim alist1 As New ArrayList()
              alist1.Add("Hello")       "Add a System.String
              alist1.Add(714)   "Add a System.Int32
              alist1.Add(New DateTime(2003, 1, 1))      "Add a System.DateTime
              alist1.Add(#1/1/2003#)    "Add a System.DateTime
              alist1.Add(4.5)   "Add a System.Double
              alist1.Add(4.5F)          "Add a System.Single
              Dim o As Object
              For Each o In alist1
                      Console.WriteLine(o & ": " & o.GetType().ToString())
              Next
  End Sub

End class</source>

Hello: System.String
714: System.Int32
01/01/2003: System.DateTime
01/01/2003: System.DateTime
4.5: System.Double
4.5: System.Single

Add user defined object to ArrayList

<source lang="vbnet">Imports System.Collections Structure Person

   Dim strLastName As String
   Dim strFirstName As String
   Dim strPhone As String
   Dim strEMail As String

End Structure

public class Test

  public Shared Sub Main
       Dim alPersons As New ArrayList
       Dim udtPerson As New Person
       "Add the first person.
       With udtPerson
           .strLastName = "S"
           .strFirstName = "J"
           .strPhone = "5"
           .strEMail = "j@s.ru"
       End With
       alPersons.Add(udtPerson)
       "Add the second person.
       With udtPerson
           .strLastName = "J"
           .strFirstName = "S"
           .strPhone = "5"
           .strEMail = "s@s.ru"
       End With
       alPersons.Add(udtPerson)
       "Create the third person.
       With udtPerson
           .strLastName = "J"
           .strFirstName = "K"
           .strPhone = "5"
           .strEMail = "k@s.ru"
       End With
       "Insert the third person, but first check if they already exists.
       If Not alPersons.Contains(udtPerson) Then
           alPersons.Insert(1, udtPerson)
       End If
       "Remove the first person.
       alPersons.RemoveAt(0)
       "Display the array list values.
       Console.WriteLine("The array list contains " & alPersons.Count & " elements.")
       For Each udtPerson In alPersons
           Console.WriteLine("NAME: " & udtPerson.strFirstName & " " & udtPerson.strLastName)
       Next udtPerson

  End Sub

End class</source>

The array list contains 2 elements.
NAME: K J
NAME: S J

Convert ArrayList to array

<source lang="vbnet">Imports System.Collections public class Test

  public Shared Sub Main
       Dim array_list As New ArrayList
       array_list.Add("A")
       array_list.Add("B")
       array_list.Add("C")
       " Array object of objects.
       Dim astring_array As Array
       astring_array = array_list.ToArray()

  End Sub
  

End class</source>

Remove element in an ArrayList by index

<source lang="vbnet">Imports System.Collections Structure Person

   Dim strLastName As String
   Dim strFirstName As String
   Dim strPhone As String
   Dim strEMail As String

End Structure

public class Test

  public Shared Sub Main
       Dim alPersons As New ArrayList
       Dim udtPerson As New Person
       "Add the first person.
       With udtPerson
           .strLastName = "S"
           .strFirstName = "J"
           .strPhone = "5"
           .strEMail = "j@s.ru"
       End With
       alPersons.Add(udtPerson)
       "Add the second person.
       With udtPerson
           .strLastName = "J"
           .strFirstName = "S"
           .strPhone = "5"
           .strEMail = "s@s.ru"
       End With
       alPersons.Add(udtPerson)
       "Create the third person.
       With udtPerson
           .strLastName = "J"
           .strFirstName = "K"
           .strPhone = "5"
           .strEMail = "k@s.ru"
       End With
       "Insert the third person, but first check if they already exists.
       If Not alPersons.Contains(udtPerson) Then
           alPersons.Insert(1, udtPerson)
       End If
       "Remove the first person.
       alPersons.RemoveAt(0)
       "Display the array list values.
       Console.WriteLine("The array list contains " & alPersons.Count & " elements.")
       For Each udtPerson In alPersons
           Console.WriteLine("NAME: " & udtPerson.strFirstName & " " & udtPerson.strLastName)
       Next udtPerson

  End Sub

End class</source>

The array list contains 2 elements.
NAME: K J
NAME: S J

Use ArrayList.Contains to check if a object already exists

<source lang="vbnet">Imports System.Collections Structure Person

   Dim strLastName As String
   Dim strFirstName As String
   Dim strPhone As String
   Dim strEMail As String

End Structure

public class Test

  public Shared Sub Main
       Dim alPersons As New ArrayList
       Dim udtPerson As New Person
       "Add the first person.
       With udtPerson
           .strLastName = "S"
           .strFirstName = "J"
           .strPhone = "5"
           .strEMail = "j@s.ru"
       End With
       alPersons.Add(udtPerson)
       "Add the second person.
       With udtPerson
           .strLastName = "J"
           .strFirstName = "S"
           .strPhone = "5"
           .strEMail = "s@s.ru"
       End With
       alPersons.Add(udtPerson)
       "Create the third person.
       With udtPerson
           .strLastName = "J"
           .strFirstName = "K"
           .strPhone = "5"
           .strEMail = "k@s.ru"
       End With
       "Insert the third person, but first check if they already exists.
       If Not alPersons.Contains(udtPerson) Then
           alPersons.Insert(1, udtPerson)
       End If
       "Remove the first person.
       alPersons.RemoveAt(0)
       "Display the array list values.
       Console.WriteLine("The array list contains " & alPersons.Count & " elements.")
       For Each udtPerson In alPersons
           Console.WriteLine("NAME: " & udtPerson.strFirstName & " " & udtPerson.strLastName)
       Next udtPerson

  End Sub

End class</source>

The array list contains 2 elements.
NAME: K J
NAME: S J

Use ArrayList to store objects

<source lang="vbnet">Option Strict On

Imports System
Imports System.Collections

Public Class Employee
    Private myEmpID As Integer
    Public Sub New(ByVal empID As Integer)
        Me.myEmpID = empID
    End Sub "New
    Public Overrides Function ToString( ) As String
        Return myEmpID.ToString( )
    End Function "ToString
    Public Property EmpID( ) As Integer
        Get
            Return myEmpID
        End Get
        Set(ByVal Value As Integer)
            myEmpID = Value
        End Set
    End Property
End Class "Employee
Class Tester
    Shared Sub Main( )
        Dim empArray As New ArrayList( )
        Dim intArray As New ArrayList( )
        Dim i As Integer
        For i = 0 To 4
            empArray.Add(New Employee(i + 100))
            intArray.Add((i * 5))
        Next i
        For Each i In intArray
            Console.Write("{0} ", i.ToString( ))
        Next i
        Console.WriteLine(ControlChars.Lf)
        Dim e As Employee
        For Each e In empArray
            Console.Write("{0} ", e.ToString( ))
        Next e
        Console.WriteLine(ControlChars.Lf)
        Console.WriteLine("empArray.Capacity: {0}", empArray.Capacity)
    End Sub
End Class</source>

0 5 10 15 20
100 101 102 103 104
empArray.Capacity: 8

Use DirectCast to convert ArrayList to array

<source lang="vbnet">Imports System.Collections public class Test

  public Shared Sub Main
       Dim array_list As New ArrayList
       array_list.Add("A")
       array_list.Add("B")
       array_list.Add("C")
       " Array of strings.
       Dim string_array() As String
       string_array = DirectCast(array_list.ToArray(GetType(String)), String())

  End Sub
  

End class</source>

Use For Each to loop through the ArrayList

<source lang="vbnet">Imports System.Collections Structure Person

   Dim strLastName As String
   Dim strFirstName As String
   Dim strPhone As String
   Dim strEMail As String

End Structure

public class Test

  public Shared Sub Main
       Dim alPersons As New ArrayList
       Dim udtPerson As New Person
       "Add the first person.
       With udtPerson
           .strLastName = "S"
           .strFirstName = "J"
           .strPhone = "5"
           .strEMail = "j@s.ru"
       End With
       alPersons.Add(udtPerson)
       "Add the second person.
       With udtPerson
           .strLastName = "J"
           .strFirstName = "S"
           .strPhone = "5"
           .strEMail = "s@s.ru"
       End With
       alPersons.Add(udtPerson)
       "Create the third person.
       With udtPerson
           .strLastName = "J"
           .strFirstName = "K"
           .strPhone = "5"
           .strEMail = "k@s.ru"
       End With
       "Insert the third person, but first check if they already exists.
       If Not alPersons.Contains(udtPerson) Then
           alPersons.Insert(1, udtPerson)
       End If
       "Remove the first person.
       alPersons.RemoveAt(0)
       "Display the array list values.
       Console.WriteLine("The array list contains " & alPersons.Count & " elements.")
       For Each udtPerson In alPersons
           Console.WriteLine("NAME: " & udtPerson.strFirstName & " " & udtPerson.strLastName)
       Next udtPerson

  End Sub

End class</source>

The array list contains 2 elements.
NAME: K J
NAME: S J