检查网络连接

Question

我正在构建一个简单的应用程序来监听NetworkAvailibilityChanged 事件。一切都很好，除了调制解调器 PPP 接口连接，应用程序仅在网络连接时才收到可用性通知，而在断开连接时不会收到通知。

我错过了什么吗？我在局域网上试了一下，效果很好。

Answer 1

这是 NetworkAvailbilityChanged 所涉及的内容。

Friend Shared Function InternalGetIsNetworkAvailable() As Boolean
    If ComNetOS.IsWinNt Then
        Dim interface2 As NetworkInterface
        For Each interface2 In SystemNetworkInterface.GetNetworkInterfaces
            If (((interface2.OperationalStatus = OperationalStatus.Up) AndAlso (interface2.NetworkInterfaceType <> NetworkInterfaceType.Tunnel)) AndAlso (interface2.NetworkInterfaceType <> NetworkInterfaceType.Loopback)) Then
                Return True
            End If
        Next
        Return False
    End If
    Dim flags As UInt32 = 0
    Return UnsafeWinINetNativeMethods.InternetGetConnectedState((flags), 0)
End Function

Private Shared Sub ChangedAddress(ByVal sender As Object, ByVal eventArgs As EventArgs)
    SyncLock AvailabilityChangeListener.syncObject
        Dim isNetworkAvailable As Boolean = SystemNetworkInterface.InternalGetIsNetworkAvailable
        If (isNetworkAvailable <> AvailabilityChangeListener.isAvailable) Then
            AvailabilityChangeListener.isAvailable = isNetworkAvailable
            Dim array As DictionaryEntry() = New DictionaryEntry(AvailabilityChangeListener.s_availabilityCallerArray.Count  - 1) {}
            AvailabilityChangeListener.s_availabilityCallerArray.CopyTo(array, 0)
            Dim i As Integer
            For i = 0 To array.Length - 1
                Dim key As NetworkAvailabilityChangedEventHandler = DirectCast(array(i).Key, NetworkAvailabilityChangedEventHandler)
                Dim context As ExecutionContext = DirectCast(array(i).Value, ExecutionContext)
                If (context Is Nothing) Then
                    key.Invoke(Nothing, New NetworkAvailabilityEventArgs(AvailabilityChangeListener.isAvailable))
                Else
                    ExecutionContext.Run(context.CreateCopy, AvailabilityChangeListener.s_RunHandlerCallback, key)
                End If
            Next i
        End If
    End SyncLock
End Sub

根据这些看来，如果它告诉你有网络，它也应该告诉你没有网络。它似乎也适用于每个设备的地址。当地址发生变化时，它会调用 ChangedAddress。

看看这些，看看你是否更清楚地了解幕后发生的事情。