心情

非泛型下的自定义集合的实现
该例子仅仅具有简单的迭代功能
--共定义了3个类: Person,PersonEnum,People
Imports System
Imports System.Collections

Public Class Person
Public Sub New(ByVal fName As String, ByVal lName As String)
Me.firstName = fName
Me.lastName = lName
End Sub

Public firstName As String
Public lastName As String
End Class

Public Class People
Implements IEnumerable
Private _people() As Person
Public Sub New(ByVal pArray() As Person)
_people = New Person(pArray.Length - 1) {}
Dim i As Integer
For i = 0 To pArray.Length - 1
  _people(i) = pArray(i)
Next i
End Sub
Public Function GetEnumerator() As IEnumerator _
  Implements IEnumerable.GetEnumerator
Return New PeopleEnum(_people)
End Function
End Class

Public Class PeopleEnum
Implements IEnumerator
Public _people() As Person
' Enumerators are positioned before the first element
' until the first MoveNext() call.
Dim position As Integer = -1
Public Sub New(ByVal list() As Person)
_people = list
End Sub
Public Function MoveNext() As Boolean Implements IEnumerator.MoveNext
position = position + 1
Return (position < _people.Length)
End Function
Public Sub Reset() Implements IEnumerator.Reset
position = -1
End Sub
Public ReadOnly Property Current() As Object Implements IEnumerator.Current
Get
  Try
  Return _people(position)
  Catch ex As IndexOutOfRangeException
  Throw New InvalidOperationException()
  End Try
End Get
End Property
End Class

Module Module1
Sub Main()
Dim peopleArray() As Person = { _
  New Person("John", "Smith"), _
  New Person("Jim", "Johnson"), _
  New Person("Sue", "Rabon")}
Dim peopleList As New People(peopleArray)
Dim p As Person
For Each p In peopleList
  Console.WriteLine(p.firstName + " " + p.lastName)
Next
End Sub
End Module

' This code produces output similar to the following:
'
' John Smith
' Jim Johnson
' Sue Rabon