Public Class frmClassBindingDemo
 
    Dim tbo As New TextBox With {.Parent = Me}
 
    Dim ggg As New wTest
 
    Dim WithEvents btn As New Button With _
        {.Parent = Me, .Top = 50, .Text = "ChangeKey"}
 
    Private Sub frmClassBindingDemo_Load(sender As System.Object, _
                        e As System.EventArgs) Handles MyBase.Load
 
        With ggg
            .T3Key = "AA"
            .T3 = "T3AA"
            .T3Key = "BB"
            .T3 = "T3BB"
            .T3Key = "AA"
        End With
 
        Try
            tbo.DataBindings.Add("Text", ggg, "T3", False, _
              DataSourceUpdateMode.OnPropertyChanged)
        Catch ex As Exception
            MsgBox(ex.ToString)
        End Try
    End Sub
 
    Private Sub btn_Click(sender As Object, e As System.EventArgs) Handles _
      btn.Click
        If ggg.T3Key = "AA" Then ggg.T3Key = "BB" Else ggg.T3Key = "AA"
    End Sub
 
    Public Class wTest
        Implements System.ComponentModel.INotifyPropertyChanged
 
        Public Event PropertyChanged(sender As Object, _
            e As System.ComponentModel.PropertyChangedEventArgs) _
            Implements _
            System.ComponentModel.INotifyPropertyChanged.PropertyChanged
 
        Private mAA As String
        Private mBB As String
        Private mT3Key As String = "AA"
 
        Public Property T3Key() As String
            Set(value As String)
                If Not mT3Key = value Then
                    mT3Key = value
                    RaiseEvent PropertyChanged _
                    (Me, New System.ComponentModel.PropertyChangedEventArgs( _
                    "T3Key"))
                    RaiseEvent PropertyChanged _
                    (Me, New System.ComponentModel.PropertyChangedEventArgs( _
                    "T3"))
                End If
            End Set
            Get
                Return mT3Key
            End Get
        End Property
 
        Public Property T3() As String
            Get
                Select Case mT3Key
                    Case "AA"
                        Return mAA
                    Case "BB"
                        Return mBB
                    Case Else
                        Return ""
                End Select
            End Get
            Set(ByVal value As String)
                Dim changed As Boolean = False
                Select Case mT3Key
                    Case "AA"
                        If Not mAA = value Then
                            mAA = value
                            changed = True
                        End If
                    Case "BB"
                        If Not mBB = value Then
                            mBB = value
                            changed = True
                        End If
                End Select
                If changed Then
                    RaiseEvent PropertyChanged _
                    (Me, New System.ComponentModel.PropertyChangedEventArgs( _
                    "T3"))
                End If
            End Set
        End Property
    End Class
 
End Class