VB.Net Tutorial/Collections/Collection

Add key value pair to Collection

Option Strict On
Imports System.Collections
Public Class Collect
   Public Shared Sub Main()
      Dim sta As New Collection
         sta.Add("New York", "NY")
         sta.Add("Michigan", "MI")
         sta.Add("New Jersey", "NJ")
         sta.Add("Massachusetts", "MA")
      For Each stcode As String In sta
         Console.WriteLine(stcode)
      Next
   End Sub
End Class

New York
Michigan
New Jersey
Massachusetts

Deleting the members of a collection

Option Strict On
Public Module CollectionTest
   Public Sub Main()
      Dim weights As New Collection
      weights.Add("ounces", "oz")
      weights.Add("pounds", "lbs")
      weights.Add("kilograms", "kg")
      weights.Add("milligrams", "mg")
      For ordinal As Integer = weights.Count To 1 Step -1
         weights.Remove(ordinal)
      Next
      Console.WriteLine("The collection now has {0} items.", weights.Count)
   End Sub
End Module

The collection now has 0 items.

Get Enumerator from Collection

Imports System.Collections
Public Class Enumerate
   Public Shared Sub Main()
      Dim weights As New Collection
      Dim iterator As IEnumerator
      weights.Add("ounces", "oz")
      weights.Add("pounds", "lbs")
      weights.Add("kilograms", "kg")
      weights.Add("milligrams", "mg")
      iterator = weights.GetEnumerator
      Do While iterator.MoveNext
         Console.WriteLine(iterator.Current)
      Loop
   End Sub
End Class

ounces
pounds
kilograms
milligrams

Inserting items into a collection by index

Public Class Tester
    Public Shared Sub Main
        Dim wordCollection As New Collection
        wordCollection.Add("This")
        wordCollection.Add("is")
        wordCollection.Add("a")
        wordCollection.Add("collection")
        wordCollection.Add("of")
        wordCollection.Add("words")
        " ----- Insert a word after item 3.
        wordCollection.Add("slightly", , , 3)
        " ----- Insert a word before item 5.
        wordCollection.Add("longer", , 5)
        For Each word As String In wordCollection
            Console.WriteLine(word)
        Next word
    End Sub
End Class

This
is
a
slightly
longer
collection
of
words

Remove from Collection

public class Test
   public Shared Sub Main
        Dim employees As New Collection
        employees.Add(New Employee("A"))
        employees.Add(New Manager("B"))
        employees.Add(New Manager("C"))
        employees.Add(New Employee("D"))
        For Each emp As Employee In employees
            Console.WriteLine(emp.Name)
        Next emp
        
        For i As Integer = employees.Count To 1 Step -1
            Dim emp As Employee = CType(employees(i), Employee)
            If emp.IsManager Then employees.Remove(i)
        Next i
        For Each emp As Employee In employees
            Console.WriteLine(emp.Name)
        Next emp
   End Sub
End class
Public Class Employee
    Public Name As String
    Public Sub New(ByVal new_name As String)
        Name = new_name
    End Sub
    Public Overridable Function IsManager() As Boolean
        Return False
    End Function
End Class
Public Class Customer
    Public Name As String
    Public Sub New(ByVal new_name As String)
        Name = new_name
    End Sub
End Class
Public Class Manager
    Inherits Employee
    Public Sub New(ByVal new_name As String)
        MyBase.new(new_name)
    End Sub
    Public Overrides Function IsManager() As Boolean
        Return True
    End Function
End Class

A
B
C
D
A
D

Scanning items in a collection

Public Class Tester
    Public Shared Sub Main
        Dim numberCollection As New Collection
        numberCollection.Add(14, "C")
        numberCollection.Add(25, "D")
        numberCollection.Add(36, "E")
        numberCollection.Add(47, "A")
        numberCollection.Add(58, "B")
        " ----- Scan the collection with a loop counter.
        "       Collections are base-1, not base-0.
        For counter As Integer = 1 To numberCollection.Count
            Console.WriteLine(numberCollection(counter))
        Next counter
        " ----- Scan the collection by item.
        For Each number As Integer In numberCollection
            Console.WriteLine(number)
        Next number
        " ----- Retrieve items by key.
        Console.WriteLine(numberCollection("A"))
        Console.WriteLine(numberCollection("B"))
        Console.WriteLine(numberCollection("C"))
        Console.WriteLine(numberCollection("D"))
        Console.WriteLine(numberCollection("E"))

    End Sub
End Class

14
25
36
47
58
14
25
36
47
58
47
58
14
25
36

Store objects in Collection and retrieve by key and index

Imports System
 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 intCollection As New Collection( )
         Dim empCollection As New Collection( )
         Dim empCollection2 As New Collection( )
         Dim i As Integer
         For i = 0 To 4
             empCollection.Add(New Employee(i + 100))
             intCollection.Add((i * 5))
         Next i
         empCollection2.Add(New Employee(1), "G")
         empCollection2.Add(New Employee(2), "J")
         empCollection2.Add(New Employee(3), "T")
         For Each i In intCollection
             Console.Write("{0} ", i.ToString( ))
         Next i
         Console.WriteLine( )
         Console.WriteLine("Employee collection...")
         Dim e As Employee
         For Each e In empCollection
             Console.Write("{0} ", e.ToString( ))
         Next e
         Console.WriteLine( )
         Console.WriteLine("Employee collection 2...")
         For Each e In empCollection2
             Console.Write("{0} ", e.ToString( ))
         Next e
         Console.WriteLine( )
         Dim emp As Employee
         emp = empCollection2.Item("J")
         Console.WriteLine(emp.ToString( ))
         emp = empCollection2.Item(1)
         Console.WriteLine("Index(1) retrieved empID {0}", emp.ToString( ))
     End Sub 
 End Class

0 5 10 15 20
Employee collection...
100 101 102 103 104
Employee collection 2...
1 2 3
2
Index(1) retrieved empID 1