Memento in VB.NET

   1:      ' Memento Design Pattern.

   2:      ' See description in //www.vb-net.com/ProgramTheory/Memento.htm

   3:      Class MainApp

   4:          ' Entry point into console application.

   5:          Public Shared Sub Main()

   6:              Dim o As New Originator()

   7:              o.State = "On"

   8:              ' Store internal state

   9:              Dim c As New Caretaker()

  10:              c.Memento = o.CreateMemento()

  11:              ' Continue changing originator

  12:              o.State = "Off"

  13:              ' Restore saved state

  14:              o.SetMemento(c.Memento)

  15:              ' Wait for user

  16:              Console.ReadKey()

  17:          End Sub

  18:      End Class

  19:   

  20:      ' The 'Originator' class

  21:      Class Originator

  22:          Private _state As String

  23:          ' Property

  24:          Public Property State() As String

  25:              Get

  26:                  Return _state

  27:              End Get

  28:              Set(value As String)

  29:                  _state = value

  30:                  Console.WriteLine(Convert.ToString("State = ") & _state)

  31:              End Set

  32:          End Property

  33:          ' Creates memento 

  34:          Public Function CreateMemento() As Memento

  35:              Return (New Memento(_state))

  36:          End Function

  37:          ' Restores original state

  38:          Public Sub SetMemento(memento As Memento)

  39:              Console.WriteLine("Restoring state...")

  40:              State = memento.State

  41:          End Sub

  42:      End Class

  43:   

  44:      ' The 'Memento' class

  45:      Class Memento

  46:          Private _state As String

  47:          ' Constructor

  48:          Public Sub New(state As String)

  49:              Me._state = state

  50:          End Sub

  51:          ' Gets or sets state

  52:          Public ReadOnly Property State() As String

  53:              Get

  54:                  Return _state

  55:              End Get

  56:          End Property

  57:      End Class

  58:   

  59:      ' The 'Caretaker' class

  60:      Class Caretaker

  61:          Private _memento As Memento

  62:          ' Gets or sets memento

  63:          Public Property Memento() As Memento

  64:              Get

  65:                  Return _memento

  66:              End Get

  67:              Set(value As Memento)

  68:                  _memento = value

  69:              End Set

  70:          End Property

  71:      End Class