VB.Net Tutorial/Collections/ArrayList

Add different data types to ArrayList

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

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

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

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

Convert ArrayList to array

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

Remove element in an ArrayList by index

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

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

Use ArrayList.Contains to check if a object already exists

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

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

Use ArrayList to store objects

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

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

Use DirectCast to convert ArrayList to array

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

Use For Each to loop through the ArrayList

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

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