Vb.net Cisco AnyConnect的AddHandler

我正在尝试创建代码来自动检测VPN连接和常规internet连接的中断（以及当它重新连接到两者时）

我已尝试使用VpnApiClass（intellisense中的每个操作）和NetworkChange.NetworkAvailabilityChanged添加处理程序。NetworkChange.NetworkAvailabilityChanged适用于internet断开，但如果仅VPN断开，则不适用

    '''''VB.NET:
    Private Sub Main_Load(sender As Object, e as EventArgs) Handles MyBase.Load
       Dim tmpVpn as New NpnApiClass

       AddHandler tmpVpn.VpnStateNotification, AddressOf NetworkConnectionChanged
       AddHandler tmpVpn.VpnEventAvailableNotification, AddressOf NetworkConnectionChanged
       AddHandler NetworkChange.NetworkAvailabilityChanged, AddressOf NetworkConnectionChanged
    End Sub

    Private Sub NetworkConnectionChanged()
       '''''Note: CommonElements is a dll file I'm referencing, function returns a boolean (True if connected, False if disconnected).
       If Not CommonElements.isConnectedToNetwork_NetworkInterface() Then
           Main.AddFiles.Enabled = False
           Main.RemoveFiles.Enabled = False
           Status.Text = "Disconnected"
       Else
           Main.AddFiles.Enabled = True
           Main.RemoveFiles.Enabled = True
           Status.Text = "Connected"
       End If
    End Sub

当从VPN断开连接时，希望看到主窗体上的按钮禁用按钮并更新状态标签文本。然后启用按钮，并在重新连接到VPN时更新状态标签文本。取而代之的是，除了从我的笔记本电脑上拔下以太网线，它不会更新任何东西。没有错误或未处理的异常