Imports System
Imports System.Collections.Generic
Imports System.Collections.ObjectModel
 
Public Class Dinosaurs
    Inherits Collection(Of String)
 
    Public Event Changed As EventHandler(Of DinosaursChangedEventArgs)
 
    Protected Overrides Sub InsertItem( _
        ByVal index As Integer, ByVal newItem As String)
 
        MyBase.InsertItem(index, newItem)
 
        RaiseEvent Changed(Me, New DinosaursChangedEventArgs( _
            ChangeType.Added, newItem, Nothing))
    End Sub
 
    Protected Overrides Sub SetItem(ByVal index As Integer, _
        ByVal newItem As String)
 
        Dim replaced As String = Items(index)
        MyBase.SetItem(index, newItem)
 
        RaiseEvent Changed(Me, New DinosaursChangedEventArgs( _
            ChangeType.Replaced, replaced, newItem))
    End Sub
 
    Protected Overrides Sub RemoveItem(ByVal index As Integer)
 
        Dim removedItem As String = Items(index)
        MyBase.RemoveItem(index)
 
        RaiseEvent Changed(Me, New DinosaursChangedEventArgs( _
            ChangeType.Removed, removedItem, Nothing))
    End Sub
 
    Protected Overrides Sub ClearItems()
        MyBase.ClearItems()
 
        RaiseEvent Changed(Me, New DinosaursChangedEventArgs( _
            ChangeType.Cleared, Nothing, Nothing))
    End Sub
 
End Class
 
' Event argument for the Changed event.
'
Public Class DinosaursChangedEventArgs
    Inherits EventArgs
 
    Public ReadOnly ChangedItem As String
    Public ReadOnly ChangeType As ChangeType
    Public ReadOnly ReplacedWith As String
 
    Public Sub New(ByVal change As ChangeType, ByVal item As String, _
        ByVal replacement As String)
 
        ChangeType = change
        ChangedItem = item
        ReplacedWith = replacement
    End Sub
End Class
 
Public Enum ChangeType
    Added
    Removed
    Replaced
    Cleared
End Enum
 
Public Class Demo
 
    Public Shared Sub Main() 
 
        Dim dinosaurs As New Dinosaurs
 
        AddHandler dinosaurs.Changed, AddressOf ChangedHandler
 
        dinosaurs.Add("Psitticosaurus")
        dinosaurs.Add("Caudipteryx")
        dinosaurs.Add("Compsognathus")
        dinosaurs.Add("Muttaburrasaurus")
 
        Display(dinosaurs)
 
        Console.WriteLine(vbLf & "IndexOf(""Muttaburrasaurus""): {0}", _
            dinosaurs.IndexOf("Muttaburrasaurus"))
 
        Console.WriteLine(vbLf & "Contains(""Caudipteryx""): {0}", _
            dinosaurs.Contains("Caudipteryx"))
 
        Console.WriteLine(vbLf & "Insert(2, ""Nanotyrannus"")")
        dinosaurs.Insert(2, "Nanotyrannus")
 
        Console.WriteLine(vbLf & "dinosaurs(2): {0}", dinosaurs(2))
 
        Console.WriteLine(vbLf & "dinosaurs(2) = ""Microraptor""")
        dinosaurs(2) = "Microraptor"
 
        Console.WriteLine(vbLf & "Remove(""Microraptor"")")
        dinosaurs.Remove("Microraptor")
 
        Console.WriteLine(vbLf & "RemoveAt(0)")
        dinosaurs.RemoveAt(0)
 
        Display(dinosaurs)
 
    End Sub
 
    Private Shared Sub Display(ByVal cs As Collection(Of String)) 
        Console.WriteLine()
        For Each item As String In cs
            Console.WriteLine(item)
        Next item
    End Sub
 
    Private Shared Sub ChangedHandler(ByVal source As Object, _
        ByVal e As DinosaursChangedEventArgs)
 
        If e.ChangeType = ChangeType.Replaced Then
            Console.WriteLine("{0} was replaced with {1}", _
                e.ChangedItem, e.ReplacedWith)
 
        ElseIf e.ChangeType = ChangeType.Cleared Then
            Console.WriteLine("The dinosaur list was cleared.")
 
        Else
            Console.WriteLine("{0} was {1}.", _
                e.ChangedItem, e.ChangeType)
        End If
    End Sub
 
End Class
 
' This code example produces the following output:
'
'Psitticosaurus was Added.
'Caudipteryx was Added.
'Compsognathus was Added.
'Muttaburrasaurus was Added.
'
'Psitticosaurus
'Caudipteryx
'Compsognathus
'Muttaburrasaurus
'
'IndexOf("Muttaburrasaurus"): 3
'
'Contains("Caudipteryx"): True
'
'Insert(2, "Nanotyrannus")
'Nanotyrannus was Added.
'
'dinosaurs(2): Nanotyrannus
'
'dinosaurs(2) = "Microraptor"
'Nanotyrannus was replaced with Microraptor
'
'Remove("Microraptor")
'Microraptor was Removed.
'
'RemoveAt(0)
'Psitticosaurus was Removed.
'
'Caudipteryx
'Compsognathus
'Muttaburrasaurus