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。机器在车内（移动物体）。

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

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

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，NetworkAvailabilityChanged事件未被触发。因此它每5秒抛出以下错误，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：我每隔5秒向SQL Server计算机发出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，请NetworkAvailabilityChanged event is fired。问题出在汽车驶出网络时。

是否还有其他可行的解决方案来检测无线网络状态？

Answer 1

确实有。

为什么当你可以检查你是否连接到本地wifi时，为某些虚拟网站发送http请求。使用ManagedWifi API，这将消除您面临的减速。

//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Voila！你完成了。

Answer 2

将您的代码更改为

(Get-Content $path)

Answer 3

您也可以使用WebRequest检查您是否有互联网连接：

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

我只想使用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，然后决定下一步做什么，最后你可以执行更多的代码而不管正在检索的数据

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

检测.NET

4 个答案: