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Collections, IEnumerable & IEnumerator (Part 2)

Collections, IEnumerable & IEnumerator (Part 2)

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AdamSpeight2008
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20 Oct, 2009 - 06:36 PM

Post #1

Continuation from Part 1
Collections, IEnumerable & IEnumerator (Part 2)

What's an Enumerable?
An Enumerable is a class that implements the IEnumerable interface
The IEnumerable

CODE

Public Class Example
Implements IEnumerable

Public Function GetEnumerator() As System.Collections.IEnumerator Implements System.Collections.IEnumerable.GetEnumerator

End Function
End Class

That function returns an Enumemator for the class.

What's an Enumerator
An Enumerator is a class that implements the IEnumerator Interface. It more detail an Enumerator is a method of iterating through the values of a collection.

CODE

Public Class IEnumerator_Example
Implements IEnumerator

Public ReadOnly Property Current() As Object Implements System.Collections.IEnumerator.Current
Get

End Get
End Property

Public Function MoveNext() As Boolean Implements System.Collections.IEnumerator.MoveNext

End Function

Public Sub Reset() Implements System.Collections.IEnumerator.Reset

End Sub
End Class

So you can see why you the error (shown in Part 1)

Example of a class that uses IEnumerable and IEnumerator

CODE

Public Class MyStrings
Implements IEnumerator, IEnumerable

Private mb As String = {", "B", "C", "D"}
Private i As Integer = -1
Public Function GetEnumerator() As IEnumerator Implements IEnumerable.GetEnumerator
  Return CType(Me, IEnumerator)
End Function

Public ReadOnly Property Current() As Object Implements System.Collections.IEnumerator.Current
  Get
   If i < mb.Count Then
    Return mb(i)
   Else
    Return Nothing
   End If
  End Get
End Property

Public Function MoveNext() As Boolean Implements System.Collections.IEnumerator.MoveNext
  If i < mb.Count Then
   i += 1
   Return True
  Else
   Return False
  End If

End Function

Public Sub Reset() Implements System.Collections.IEnumerator.Reset
  i = -1
End Sub

End Class

Example Usage

CODE

Module Module1

Sub Main()
  Dim bl As New MyStrings
  For Each a In bl
   Console.WriteLine(a)

  Next
End Sub
End Module

Edit: Added link to Part 1.