Control and monitor Web-IO Digital with VB.Net

1. Combining the various operating elements and display objects in the VB.net form

In addition to the objects shown here, the program also needs a timer for polling (timer_polling).

When naming the individual objects it is helpful to use logical names. In this example the first part of the name describes the type of object and the second part the function.

1. Starting the program

While the structure of graphical user interfaces in VB.net is just as easy to accomplish as with VB5 or VB6, the network communication under VB.net is somewhat more difficult to construct than with its predecessor. This is primarily because Microsoft no longer provides the Winsock control element with VB.net. Instead, network access requires that the Import Statement be used to instance the namespace for the socket classes used in the header of the source text.

In addition, the socket on which communication will be handled must be created and a buffer for the input data needs to be defined.

					
						Imports System.Net
						Imports System.Net.Sockets
						Imports System.IO
						Imports System.Windows.Forms
						Public Class Form1
							Inherits System.Windows.Forms.Form
							Dim TCP_client As Socket
							Dim receivebuffer(511) As Byte
					
				

2. Connection control

Establishing the connection
The connection is opened by entering the IP address of the Web-IO in the text field ed_ip and clicking on the bt_connect button.

						
							Private Sub bt_connect_Click(ByVal sender As System.Object, _
							ByVal e As System.EventArgs) Handles bt_connect.Click
								Dim webioep As New IPEndPoint(IPAddress.Parse(tb_ip.Text), Val(tb_port.Text))
								If tb_ip.Text <> "" And tb_port.Text <> "" Then
								TCP_client = New Socket(AddressFamily.InterNetwork, SocketType.Stream, _
								ProtocolType.Tcp)
								bt_connect.Enabled = False
									Try
										TCP_client.BeginConnect(webioep, New AsyncCallback(AddressOf callback_connect), _
										TCP_client)
									Catch ex As Exception
										closeconnections()
										MessageBox.Show(ex.Message, "Socket Error", MessageBoxButtons.OK, _
										MessageBoxIcon.Error)
									End Try
								End If
							End Sub
						
					

Opening the connection
For TCP/IP handling first an IPEndPoint is defined from IP address and TCP port and used to initialize the TCP_client socket. As part of the connection request a reference to a callback procedure is created.

Connection is made
As soon as a connection is made with the Web-IO, the callback procedure is run. The status line shows that the connection has been opened, the operating elements are enabled for use and the Disconnect button becomes operable. The Connect button is blocked for operation. In addition a reference to a callback routine for data reception is created.

						
							Private Sub callback_connect(ByVal ar As IAsyncResult)
								bt_connect.Enabled = False
								gb_io.Enabled = True
								bt_disconnect.Enabled = True
								StatusBar1.Text = "Connected to " + tb_ip.Text + " : " + tb_port.Text
								timer_polling.Enabled = True
									Try
									TCP_client.EndConnect(ar)
									TCP_client.BeginReceive(receivebuffer, 0, 512, SocketFlags.None, New AsyncCallback(AddressOf callback_readdata), TCP_client)
									Catch ex As Exception
									closeconnections()
									StatusBar1.Text = "error on connecting"
									End Try
							End Sub
						
					

Disconnecting
The connection remains open until it is ended by the user clicking on the Disconnect button, or the Web-IO ends the connection.

						
							Private Sub bt_disconnect_Click(ByVal sender As System.Object, _
							ByVal e As System.EventArgs) Handles bt_disconnect.Click
								bt_disconnect.Enabled = False
								closeconnections()
							End Sub
						
					

In this case a corresponding procedure is invoked.

						
							Private Sub closeconnections()
								Dim ar As IAsyncResult
								timer_polling.Enabled = False
								Try
									TCP_client.EndReceive(ar)
								Catch ex As Exception
								End Try
								Try
									TCP_client.Shutdown(SocketShutdown.Both)
								Catch ex As Exception
								End Try
								Try
									TCP_client.Close()
								Catch ex As Exception
								End Try
								bt_connect.Enabled = True
								gb_io.Enabled = False
								bt_disconnect.Enabled = False
								StatusBar1.Text = "no connection"
							End Sub
						
					

Connection error
All the actions affecting TCP/IP communication are carried out within the Try-instruction. If errors occur, the CloseConnection procedure is also invoked.

3. Operation and communication from the client side

As soon as a connection is made with the Web-IO, the user can use the corresponding program elements to send commands to the Web-IO.

						
							Private Sub sendcommand(ByVal sendstring As String)
								Dim senddata As Byte() = System.Text.Encoding.ASCII.GetBytes(sendstring)
								Try
								TCP_client.Send(senddata)
								Catch ex As Exception
								closeconnections()
								End Try
							End Sub
						
					

Setting the outputs
The user sets the outputs by using the two check boxes cb_outputx. The program uses the MouseUP event of this object. If a MouseUp, i.e. releasing the output check box, is used, the program carries out the corresponding procedure and - depending on whether the check box is set or not - passes the appropriate command to the Web-IO.

						
							Private Sub cb_output0_MouseUp(ByVal sender As Object, _
							ByVal e As System.Windows.Forms.MouseEventArgs) Handles cb_output0.MouseUp
								If cb_output0.Checked Then
								sendcommand("GET /outputaccess0?PW=" + tb_password.Text + "&State=ON&")
								Else
								sendcommand("GET /outputaccess0?PW=" + tb_password.Text + "&State=OFF&")
								End If
							End Sub
						
					

						
							Private Sub cb_output1_MouseUp(ByVal sender As Object, _
							ByVal e As System.Windows.Forms.MouseEventArgs) Handles cb_output1.MouseUp
								If cb_output1.Checked Then
								sendcommand("GET /outputaccess1?PW=" + tb_password.Text + "&State=ON&")
								Else
								sendcommand("GET /outputaccess1?PW=" + tb_password.Text + "&State=OFF&")
								End If
							End Sub
						
					

Query output/input status
The user can request the status of the outputs and inputs by clicking on the corresponding button.

						
							Private Sub bt_outputs_read_Click(ByVal sender As System.Object, _
							ByVal e As System.EventArgs) Handles bt_outputs_read.Click
								sendcommand("GET /output?PW=" + tb_password.Text + "&")
							End Sub
						
					

						
						Private Sub bt_inputs_read_Click(ByVal sender As System.Object, _
							ByVal e As System.EventArgs) Handles bt_inputs_read.Click
								sendcommand("GET /input?PW=" + tb_password.Text + "&")
							End Sub
						
					

Read/clear counters
Also the counter states of the input counters can be read or cleared.

						
							Private Sub bt_counter_read0_Click(ByVal sender As System.Object, _
							ByVal e As System.EventArgs) Handles bt_counter_read0.Click
								sendcommand("GET /counter0?PW=" + tb_password.Text + "&")
							End Sub
						
					

						
							Private Sub bt_counter_read1_Click(ByVal sender As System.Object, _
							ByVal e As System.EventArgs) Handles bt_counter_read0.Click
								sendcommand("GET /counter1?PW=" + tb_password.Text + "&")
							End Sub
						
					

						
							Private Sub bt_counter_clear0_Click(ByVal sender As System.Object, _
							ByVal e As System.EventArgs) Handles bt_counter_clear0.Click
								sendcommand("GET /counterclear0?PW=" + tb_password.Text + "&")
							End Sub
						
					

						
							Private Sub bt_counter_clear1_Click(ByVal sender As System.Object, _
							ByVal e As System.EventArgs) Handles bt_counter_clear0.Click
								sendcommand("GET /counterclear1?PW=" + tb_password.Text + "&")
							End Sub
						
					

Of course all the counters can be read or cleared at the same time.

						
							Private Sub bt_counter_readall_Click(ByVal sender As System.Object, _
							ByVal e As System.EventArgs) Handles bt_counter_readall.Click
								sendcommand("GET /counter?PW=" + tb_password.Text + "&")
							End Sub
						
					

						
							Private Sub bt_counter_clearall_Click(ByVal sender As System.Object, _
							ByVal e As System.EventArgs) Handles bt_counter_clearall.Click
								sendcommand("GET /counterclear?PW=" + tb_password.Text + "&")
							End Sub
						
					

3. Data reception from the Web-IO

• Process and display the received data
  All commands and requests to the Web-IO are acknowledged with a reply string. The replies have a specific structure depending on the type.
• For the outputs: output;<binary value of the output status in hexadecimal format>
• For the inputs: input;<binary value of the input status in hexadecimal format>
• For the counters: counterx;<decimal counter state>
• or counter;<decimal counter state 0 >; <decimal counter state 0 >;.....if you want to read all counters at the same time.
• All reply strings are finished off with a 0 byte.
• When data are received the corresponding Callback procedure is invoked

						
							Private Sub callback_readdata(ByVal ar As IAsyncResult)
								If TCP_client.Connected Then
								Dim bytesread As Integer
								Try
								bytesread = TCP_client.EndReceive(ar)
								Catch ex As Exception
								End Try
								If bytesread = 0 Then
								closeconnections()
								Else
								Dim receivestring As String
								receivestring = System.Text.Encoding.ASCII.GetString(receivebuffer, 0, _
								receivebuffer.Length)
								receivebuffer.Clear(receivebuffer, 0, 512)
								Try
									TCP_client.BeginReceive(receivebuffer, 0, 512, SocketFlags.None, New AsyncCallback(AddressOf callback_readdata), TCP_client)
								Catch ex As Exception
									closeconnections()
								End Try
								Select Case Mid(receivestring, 1, 1)
								Case "i"
									If (Val(Mid(receivestring, 7, 1)) And 1) = 1 Then
									cb_input0.Checked = True
									Else
									cb_input0.Checked = False
									End If
									If (Val(Mid(receivestring, 7, 1)) And 2) = 2 Then
									cb_input1.Checked = True
									Else
									cb_input1.Checked = False
									End If
								Case "o"
									If (Val(Mid(receivestring, 8, 1)) And 1) = 1 Then
									cb_output0.Checked = True
									Else
									cb_output0.Checked = False
									End If
									If (Val(Mid(receivestring, 8, 1)) And 2) = 2 Then
									cb_output1.Checked = True
									Else
									cb_output1.Checked = False
									End If
								Case "c"
									Dim tabpos
									If Mid(receivestring, 8, 1) = "0" Then _
										tb_counter0.Text = Mid(receivestring, 10)
									If Mid(receivestring, 8, 1) = "1" Then _
										tb_counter1.Text = Mid(receivestring, 10)
									If Mid(receivestring, 8, 1) = ";" Then
										tabpos = InStr(9, receivestring, ";")
										tb_counter0.Text = Mid(receivestring, 9, tabpos - 9)
										tb_counter1.Text = Mid(receivestring, tabpos + 1, _
										Len(receivestring) - tabpos - 1)
									End If
								End Select
								End If
								End If
							End Sub
						
					

The Receive procedure uses the first character of the receive data to check whether these are input, output or counter messages. Depending on this, a determination is made for example as to which output has which status. With the counters it is possible both to query individual counter values as well as to read out all the counters at one time. The individual counter states are then output in decimal format in a semicolon delimited string.

4. Polling

• Cyclical polling of particular values
  In order to enable automatic refreshing of the display, a timer is used.
• Depending on the check boxes for output, input and counter polling, the corresponding information is obtained from the Web-IO at a set interval.

						
							Private Sub timer_polling_Elapsed(ByVal sender As System.Object, _
							ByVal e As System.Timers.ElapsedEventArgs) Handles timer_polling.Elapsed
								If (cb_input_polling.Checked And TCP_client.Connected) Then
								sendcommand("GET /input?PW=" + tb_password.Text + "&")
								End If
								If (cb_output_polling.Checked And TCP_client.Connected) Then
								sendcommand("GET /output?PW=" + tb_password.Text + "&")
								End If
								If (cb_output_polling.Checked And TCP_client.Connected) Then
								sendcommand("GET /output?PW=" + tb_password.Text + "&")
								End If
								If (cb_counter_polling.Checked And TCP_client.Connected) Then
								sendcommand("GET /counter?PW=" + tb_password.Text + "&")
								End If
							End Sub
						
					

The desired interval can be entered in the corresponding text field. When changes are made the timer interval is automatically adjusted.

						
							Private Sub tb_interval_TextChanged(ByVal sender As System.Object, _
							ByVal e As System.EventArgs) Handles tb_interval.TextChanged
								timer_polling.Interval = Val(tb_interval.Text)
							End Sub