Imports System
Imports System.Net
Imports System.Net.Sockets
Imports System.Text
Imports System.io
Imports System.Threading
 
Public Class Form2
    Dim conctet As Boolean = False
    Public stream As NetworkStream
    Public sr As StreamReader
    Dim client As TcpClient
    Dim TcpListener As TcpListener
    Dim portt As Integer = 20
 
    Function disconect()
        If conctet Then
               stream.Close()
            client.Close()
            TcpListener.Stop()
            sr.Close()
            Timer1.Enabled = False
            conctet = False
             Connect.ForeColor = Color.LimeGreen
            Connect.Text = "Connect"
        End If
        Return conctet
    End Function
 
 
 
    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Timer1.Tick
        If Not BackgroundWorker1.IsBusy Then
            BackgroundWorker1.CancelAsync()
            BackgroundWorker1.RunWorkerAsync()
        End If
    End Sub
 
 
    Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e _
      As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
        Try
            If conctet Then
                If client.Client.Connected Then
                    If stream.CanRead And stream.DataAvailable Then
                        sr = New StreamReader(stream)
                        Dim buffer As New StringBuilder
                        Do While sr.Peek() > 0
                                                buffer.Append(sr.ReadLine + _
                                                  vbCrLf)
                        Loop
                        e.Result = buffer.ToString
                    End If
                End If
            Else
                e.Result = "conctet"
            End If
        Catch
            e.Result = "error"
        End Try
    End Sub
 
    Private Sub BackgroundWorker1_RunWorkerCompleted(ByVal sender As Object, _
      ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles _
      BackgroundWorker1.RunWorkerCompleted
        Try
            Dim text As String = e.Result.ToString
            If text.Length > 0 And Not text = "error" Then
                        Else
                If text = "error" Then
                                    disconect()
                End If
            End If
 
        Catch
 
        End Try
    End Sub
 
 
    Private Sub Connect_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Connect.Click
        If conctet Or Connect.Text = "Disconnect" Then
            disconect()
        Else
            Try
                txtResponse.Text = ""
                             port.ReadOnly = True
                Connect.ForeColor = Color.Red
                Connect.Text = "Disconnect"
 
                TcpListener = New TcpListener(portt)
                BackgroundWorker2.RunWorkerAsync()
 
            Catch
                             disconect()
            End Try
        End If
 
 
    End Sub
 
    Private Sub BackgroundWorker2_DoWork(ByVal sender As System.Object, ByVal e _
      As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker2.DoWork
        Try
            TcpListener.Start()
            client = TcpListener.AcceptTcpClient()
            e.Result = "Connect"
        Catch
            e.Result = "error"
        End Try
    End Sub
 
    Private Sub BackgroundWorker2_RunWorkerCompleted(ByVal sender As Object, _
      ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles _
      BackgroundWorker2.RunWorkerCompleted
        Dim text As String = e.Result.ToString
 
        If text = "error" Then
                  disconect()
        Else
            stream = client.GetStream()
            sr = New StreamReader(stream)
 
            conctet = True
            Timer1.Enabled = True
        End If
    End Sub
 
 
 
 
    Private Function sendCommand(ByVal send As String) As String
        Try
            If conctet Then
                If client.Client.Connected Then
                    If stream.CanWrite Then
                                  send += vbCrLf
                        Dim data As [Byte]() = Encoding.UTF8.GetBytes(send)
                        stream.Write(data, 0, data.Length)
                        Return True
                    Else
                        Return False
                    End If
                End If
            End If
            Return False
        Catch
               disconect()
            Return False
        End Try
    End Function
End Class

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Theorie ist wenn man alles wei?, aber nichts funktioniert.
Praxis ist wenn alles funktioniert, aber niemand wei? warum.
Microsoft vereint Theorie und Praxis: Nichts funktioniert und niemand wei? warum.