从应用程序

Question

我有一个应用程序通过TCPClient连接到打印机的静态IP地址和端口号连接到Zebra QLn420标签打印机。

我们一直遇到一些软件问题＆＃34;拖延＆＃34;并且跳过一些标签，并在调查之后（通过向软件添加一些日志记录功能以在每次检查连接并实际重新连接时写出文本文件）我注意到连接似乎没有保持打开状态超过一秒钟（不是一个实数，从我的测试中可以在不到一秒到5秒或更长的时间内变化）。

在我的办公桌上进行测试时，这几乎不是问题，因为信号强度很强，以至于它立即重新连接，但在实际使用的仓库中，在某些区域信号不是这样的强大。处理连接的函数将尝试重新连接最多5秒两次，然后显示错误消息并询问是否要重新连接。

我很好奇是否有人经历过这样的事情，并且可以做些什么来解决它。据我所知，软件偶尔会丢失与打印机的连接，特别是在较弱的信号区域。但我想找到一种方法来保持连接打开，直到我关闭它或信号太弱而无法继续，因为我觉得这与＆＃34;缺失＆＃34;有很多关系。标签，肯定会影响软件的速度。

下面是我的连接代码（我自己的代码和在线发现的一些代码片段的组合）：

Public Class LabelPrinter
    Private strIP as String = "xxx.xxx.xxx.xxx"
    Private intPort As Integer = "6101"

    Private client As System.Net.Sockets.TcpClient
    Private blnConnected As Boolean = False
    Private blnValidIP As Boolean = False
    Private intTimeoutLength As Integer = 5000

    Private TimeoutTime As New Timers.Timer
    Private clntSockParams As ClientSocketParameters

    Private Structure ClientSocketParameters
        Public addrs As String
        Public prt As Integer
    End Structure

    Public Sub New(Picker As Picker, newIP As String, newPort As Integer, Optional PrinterTimeout As Integer = 5000)
        If newIP <> "" Then strIP = newIP
        If newPort <> 0 Then intPort = newPort
        intTimeoutLength = PrinterTimeout

        If newIP = "" Or newPort = 0 Then Exit Sub

        Dim ipAddress As System.Net.IPAddress = Nothing
        If Not System.Net.IPAddress.TryParse(strIP, ipAddress) Then Exit Sub
    End Sub

    Public Function Connect() As Boolean
        Try
            'connect to printer via TcpClient, need ip address and port number
            'connects without thread, hangs program for 10-20 seconds if printer is not turned on, replaced with code below to thread the connection and set timeout
            'If client Is Nothing OrElse Not client.Connected Then
            '    client = New System.Net.Sockets.TcpClient
            '    client.Connect(strIP, intPort)
            'End If

            'RRB 02/10/15 - added for loop to try to connect twice each attempt instead of only once
            For i As Integer = 1 To 2
                If client Is Nothing OrElse Not client.Connected Then
                    'uses ClientSocketParameters structure to pass to recursive function ConnectionReturned()
                    clntSockParams = New ClientSocketParameters
                    clntSockParams.addrs = strIP
                    clntSockParams.prt = intPort

                    'create client and call BeginConnect (attempts to connect on separate thread until TimeoutTime has elapsed)
                    client = New System.Net.Sockets.TcpClient
                    client.SendTimeout = intTimeoutLength
                    client.ReceiveTimeout = intTimeoutLength

                    'setup timer with timeout length and start, if timer goes past intTimeoutLength, the Timeout() function is called which closes everything and leaves client = Nothing
                    AddHandler TimeoutTime.Elapsed, AddressOf Timeout
                    TimeoutTime.Interval = intTimeoutLength
                    TimeoutTime.Start()

                    client.BeginConnect(strIP, intPort, New AsyncCallback(AddressOf ConnectionReturned), clntSockParams)

                    'keeps the program from doing anything else until BeginConnect either succeeds or fails (due to connect on separate thread)
                    Do While TimeoutTime.Enabled
                        System.Threading.Thread.Sleep(500)
                    Loop
                End If

                'if TimeoutTime is elapsed and client is Nothing, connection didn't happen, throw an error
                If client Is Nothing Then
                    blnConnected = False
                Else
                    blnConnected = True
                    Exit For
                End If
            Next
        Catch ex As Exception
            blnConnected = False
        End Try

        Return blnConnected
    End Function

    Private Sub ConnectionReturned(ByVal ar As System.IAsyncResult)
        'this method is called from the client.BeginConnect line in Connect(), make sure timer is running
        If TimeoutTime.Enabled Then
            'ensure client is initialized
            If client Is Nothing Then client = New System.Net.Sockets.TcpClient

            'keep calling ConnectionReturned until client.Connected is true
            If client.Connected Then
                TimeoutTime.Stop()
            Else
                Dim actualParameters As ClientSocketParameters = DirectCast(ar.AsyncState, ClientSocketParameters)
                client.BeginConnect(actualParameters.addrs, actualParameters.prt, New AsyncCallback(AddressOf ConnectionReturned), clntSockParams)
            End If
        End If
    End Sub

    Private Sub Timeout(ByVal sender As Object, ByVal e As EventArgs)
        'this method is only called if TimeoutTime elapsed, which means no connection was made. close the client object if needed, set to Nothing, and stop TimeoutTime
        If TimeoutTime.Enabled Then
            Try
                client.Close()
            Catch ex As Exception
            End Try
            client = Nothing
            TimeoutTime.Stop()
        End If
    End Sub

    Public Sub Disconnect()
        'need to make sure StreamWriter connection and TcpClient connection to printer are closed
        Try
            client.Close()
        Catch ex As Exception
        End Try
        client = Nothing
        blnConnected = False
    End Sub
End Class

如果需要更多信息，请与我们联系。我也可以使用其他连接类型，只要可以使用静态IP和端口（通过wifi连接）。

编辑：我已修改程序中的代码以使用System.Net.Socket类，并且连接似乎在我的初始测试中保持稳定。什么会导致这种连接方法在TCPClient似乎不在同一位置的地方工作？