检测 .NET 中的无线网络状态变化

Question

我使用VB.NET 开发了winform 应用程序。该应用程序部署在连接到无线网络的机器中。机器在车里（移动物体）。

应用程序已将DataGridView 加载了从 MSSQL Server（在远程计算机中）获取的数据。数据每 5 秒刷新一次。

我已经使用NetworkAvailabilityChanged 事件来检测网络状态。如果网络可用，则我从表中检索数据。

代码：

AddHandler NetworkChange.NetworkAvailabilityChanged, AddressOf NetworkStateChangeHandler

Public Sub NetworkStateChangeHandler(ByVal sender As Object, 
                                     ByVal e As NetworkAvailabilityEventArgs)
        If e.IsAvailable = True Then           
            g_bNetworkAlive = True            
        Else           
            g_bNetworkAlive = False
        End If
End Sub

private Sub GetData()
    If g_bNetworkAlive = True
        'code to get the data from table
    End If
End Sub

问题：

如果汽车movers out of the out of the network，则不会触发NetworkAvailabilityChanged 事件。因此它每 5 秒抛出一次以下错误，并且应用程序崩溃。

A network-related or instance-specific error occurred while establishing 
a connection to SQL Server. The server was not found or was not accessible.

临时修复：我每 5 秒向 SQL 服务器机器发出一次Ping 请求，以检测网络状态。它会影响应用程序的性能。

注意：如果我手动关闭 Wifi，NetworkAvailabilityChanged event is fired.只有当汽车离开网络时才会出现问题。

还有其他可行的方案来检测无线网络状态吗？

Answer 1

我会简单地使用try..catch，所以如果你得到异常，你可以根据它的id知道代码失败的原因，并决定下一步做什么，最后你可以执行更多的代码而不考虑数据检索与否

Private Sub GetData()
    Try 
        'code to get the data from table

    Catch ex As Exception
        ' Show the exception's message.
        MessageBox.Show(ex.Message)

        ' Show the stack trace, which is a list of methods 
        ' that are currently executing.
        MessageBox.Show("Stack Trace: " & vbCrLf & ex.StackTrace)
    Finally 
        ' This line executes whether or not the exception occurs.
        MessageBox.Show("in Finally block")
    End Try
End Sub

Answer 2

确实有。

当您可以检查您是否在本地连接到 wifi 时，为什么要向一些虚拟网站发送 http 请求。 使用ManagedWifi API，这将消除您面临的减速问题。

//Create object at the beginning of your application 
WlanClient wlanClient = new WlanClient();


//You this code to check wifi availability wherever you need
foreach (WlanInterface _interface in wlanClient.Interfaces)
{
    If (_interface.CurrentConnection.wlanAssociationAttributes.dot11Ssid.SSID!=null)
   {
      // You are connected to wifi
   }
}

编辑：如果您没有找到 dll，direct link。只需参考 Dll 和瞧！你完成了。

Answer 3

你也可以像这样使用 WebRequest 来检查你是否有互联网连接：

Private Sub GetData()

    If HasInternet AndAlso g_bNetworkAlive Then
        'code to get the data from table
    End If

End Sub

Public Shared Function HasInternet As Boolean

    Return Not (HttpGet("http://www.google.com/") = "Error")

End Function

Public Shared Function HttpGet(url As String) As String
    Dim request As WebRequest = WebRequest.Create(url)
    request.Method = "GET"
    Try
        Dim response As WebResponse = request.GetResponse()
        Dim dataStream As Stream = response.GetResponseStream()
        Dim reader As New StreamReader(dataStream)
        Dim responseFromServer As String = reader.ReadToEnd()
        reader.Close()
        dataStream.Close()
        response.Close()
        Return responseFromServer
    Catch ex As Exception
        Return "Error"
    End Try
End Function

您可以使用以下函数检查sql连接：

Private Function IsDatabaseConnected() As Boolean
    Try
        Using sqlConn As New SqlConnection("YourConnectionString")
                sqlConn.Open()
                Return (sqlConn.State = ConnectionState.Open)
        End Using
    Catch e1 As SqlException
        Return False
    Catch e2 As Exception
        Return False
    End Try
End Function

Answer 4

将代码更改为

Private Sub GetData()
    If My.Computer.Network.IsAvailable AndAlso g_bNetworkAlive
        ' code to get the data from table

    End If
End Sub