Question

I changed target framework from 3.5 to 4.0, no other changes. A simple ping which worked with 3.5, now with 4.0 the result gives Canceled=True. Any ideas what may cause this?

Public Sub StartInternetConnectionCheckEvery(ByVal seconds As Integer)
    Dim timer As New Timer()
    timer.Interval = seconds * 1000
    AddHandler timer.Tick, AddressOf CheckIsConnectedToInternet
    timer.Start()
End Sub

Private Sub CheckIsConnectedToInternetByTimer(ByVal sender As Object, ByVal e As System.EventArgs)
    CheckIsConnectedToInternet()
End Sub

Public Sub CheckIsConnectedToInternet()
    Using ping As New System.Net.NetworkInformation.Ping()
        Dim address As String = "www.google.com"

        ping.SendAsync(address, Nothing)
        AddHandler ping.PingCompleted, AddressOf OnPingResult
    End Using
End Sub

Private Sub OnPingResult(ByVal sender As Object, ByVal e As PingCompletedEventArgs)
    If e.Cancelled Then
        Trace.WriteLine("InternetHelper: Ping Cancelled")
        Return
    End If

    IsConnectedToInternet = (e.Reply.Status = IPStatus.Success)
    RaiseEvent InternetPingResult(IsConnectedToInternet)
End Sub

Answer 1

Using ping As New System.Net.NetworkInformation.Ping()
   '' etc
End Using

Yes, this is not going to work well. You are disposing the ping object before the asynchronous send can complete. You got away with it before because the Ping class didn’t implement the Dispose() method properly. That got fixed in .NET 4, feedback report is here.

The fix is simple, remove Using. Disposing it properly is not so easy when you use it asynchronously. Try it in the event or don’t bother.

Otherwise a nice demonstration how framework bug fixes can break working code 🙂