' Globale Variable
Private Shared strPath As String = Environment.SpecialFolder.MyComputer
 
    Public Property StrPathCont() As String
        Get
            Return strPath
        End Get
        Set(ByVal value As String)
            strPath = value
            If strPath = Environment.SpecialFolder.MyComputer.ToString Then
                BtnStart.Enabled = False
            ElseIf String.Compare(strPath, "", False) = 0 Then
                BtnStart.Enabled = False
            Else
                BtnStart.Enabled = True
            End If
        End Set
    End Property

' Startbutton deaktivieren
StrPathCont = ""

.SelectedPath = StrPathCont

PfadMitBackslash(StrPathCont)

 Private strPath As String = _
   System.Environment.SpecialFolder.MyComputer.ToString
 
'Das Event 
Private Event PathChanged(sender As Object, e As EventArgs)
 
Dim button1 As New Button With 
    {.Parent = Me, .Enabled = False} 'Demo, ohne Designer
 
 
Public Property StrPathCont() As String
     Get
        Return strPath
     End Get
 
     Set(ByVal value As String)
        If IO.Directory.Exists(value) Then
           strPath = value
           RaiseEvent PathChanged(Me, EventArgs.Empty)
        Else
                Throw New ArgumentException(value & " existiert nicht")
        End If
     End Set
End Property
 
 
Private Sub Path_Changed(sender As Object, e As EventArgs) Handles _
  Me.PathChanged
    button1.Enabled = True
End Sub