1. Starting the program

While constructing graphical user interfaces in Delphi 2005 is just as simple to accomplish as with the older Delphi versions, constructing network communication under Delphi.net is somewhat more difficult. This is due primarily to the fact that the ClientSocket control element for framework applications is no longer provided. Instead, you must specify the namespace for the socket classes in the uses area in order to have network access.

uses
	System.Drawing, System.Collections, System.ComponentModel,
	System.Windows.Forms, System.Data, System.Net,
	System.Net.Sockets, System.IO, System.Text, System.Configuration;

Some procedures which are not created by Delphi itself must be declared in the header of the source text. (More on the content of these procedures later)

private
	{ Private-Deklarationen }
	public
	constructor Create;
	procedure callback_connect(ari : IAsyncResult);
	procedure callback_readdata(ari : IAsyncResult);
	procedure sendcommand(sendstring : String);
	procedure close();
	end;

Furthermore, the socket on which communication is supposed to take place needs to be created and a buffer for the input data and AsyncResult variable must be defined.

var
	TCP_Client : Socket;
	ReceiveBuffer : array [0..512] of byte;
	ar : IAsyncResult;

2. Connection control

Establishing the connection

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

procedure TWinForm.bt_connect_Click(sender: System.Object; e: System.EventArgs);
	var WebioEP : IPEndPoint;
	begin
		if (tb_ip.Text <> '') and (tb_port.Text <> '') then
			begin
				bt_connect.Enabled := false;
				WebioEP := IPEndPoint.Create(IPaddress.Parse(tb_ip.Text),convert.ToInt16(tb_port.Text ));
				TCP_Client := Socket.Create (AddressFamily.InterNetwork, SocketType.Stream,ProtocolType.TCP);
				StatusBar1.Text := 'Try to connect to ' + tb_ip.Text;
				timer_polling.Enabled := true;
				try
				TCP_Client.BeginConnect(WebioEP,callback_connect, TCP_Client);
				except
				on ex : Exception
				do
					begin
						StatusBar1.Text := 'ERROR on connecting';
						close();
					end;
			end;
	end;
end;

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.

procedure TWinForm.callback_connect(ari : IAsyncResult);
	begin
		gb_io.enabled := true;
		bt_disconnect.Enabled := True;
		statusbar1.Text := 'Connected to' + tb_ip.Text;
		try
		TCP_Client.EndConnect(ari);
		TCP_Client.BeginReceive(ReceiveBuffer, 0, 512, SocketFlags.None, callback_readdata, ari.AsyncState);
		except on
		ex : Exception
		do
			begin
				StatusBar1.Text := 'ERROR on connect: ' + ex.ToString;
				close();
			end;
		end;
	end;

Disconnecting

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

In this case a corresponding procedure is invoked.

procedure TWinForm.close();
	begin
		timer_polling.Enabled := False;
		Try
			TCP_client.EndReceive(ar);
		except
		end;
		Try
			TCP_client.Shutdown(SocketShutdown.Both);
		except
		end;
		Try
			TCP_client.Close()
		except
		end;
		bt_connect.Enabled := True;
		gb_io.Enabled := False;
		bt_disconnect.Enabled := False;
		StatusBar1.Text := 'no connection';
	end;

procedure TWinForm.bt_disconnect_Click(sender: System.Object; e: System.EventArgs);
	begin
		close();
	end;

Connection error

All actions pertaining to TCP/IP communication are executed within the Try instruction. If errors occur, the CloseConnection procedure is likewise 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.

procedure TWinForm.sendcommand(sendstring: String);
	var
	SendBuffer : array[0..512] of byte;
	begin
		SendBuffer := System.Text.Encoding.ASCII.GetBytes(sendstring);
		try
			TCP_Client.Send(SendBuffer, 0, sendstring.Length, SocketFlags.None );
			except on ex : Exception
			do
			begin
				StatusBar1.Text := 'ERROR on send: ' + ex.ToString;
				close();
			end;
		end;
	end;

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.

procedure TWinForm.cb_output0_MouseUp(sender: System.Object; e: System.Windows.Forms.MouseEventArgs);
	begin
		if cb_output0.Checked Then
			sendcommand('GET /outputaccess0?PW='+ tb_password.Text + '&State=ON&')
		else
			sendcommand('GET /outputaccess0?PW='+ tb_password.Text + '&State=OFF&')q;
	end;

procedure TWinForm.cb_output1_MouseUp(sender: System.Object; e: System.Windows.Forms.MouseEventArgs);
	begin
		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;

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

procedure TWinForm.bt_outputs_read_Click(sender: System.Object; e: System.EventArgs);
	begin
		sendcommand('GET /output?PW='+ tb_password.Text + '&');
	end;

procedure TWinForm.bt_inputs_read_Click(sender: System.Object; e: System.EventArgs);
	begin
		sendcommand('GET /input?PW='+ tb_password.Text + '&');
	end;

Read/clear counters

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

procedure TWinForm.bt_counter_read0_Click(sender: System.Object; e: System.EventArgs);
	begin
		sendcommand('GET /counter0?PW='+ tb_password.Text + '&');
	end;

procedure TWinForm.bt_counter_read1_Click(sender: System.Object; e: System.EventArgs);
	begin
		sendcommand('GET /counter0?PW='+ tb_password.Text + '&');
	end;

procedure TWinForm.bt_counter_clear0_Click(sender: System.Object; e: System.EventArgs);
	begin
		sendcommand('GET /counterclear0?PW='+ tb_password.Text + '&');
	end;

procedure TWinForm.bt_counter_clear1_Click(sender: System.Object; e: System.EventArgs);
	begin
		sendcommand('GET /counterclear1?PW='+ tb_password.Text + '&');
	end;

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

procedure TWinForm.bt_counter_readall_Click(sender: System.Object; e: System.EventArgs);
	begin
		sendcommand('GET /counter?PW='+ tb_password.Text + '&');
	end;

procedure TWinForm.bt_counter_clearall_Click(sender: System.Object; e: System.EventArgs);
	begin
		sendcommand('GET /counterclear?PW='+ tb_password.Text + '&');
	end;

4. Receiving data 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

procedure TWinForm.callback_readdata(ari : IAsyncResult);
	var
		bytesread : Integer;
		receivestring : string;
	begin
		try
			bytesread := TCP_Client.EndReceive(ari)
		except
		end;
		if Bytesread = 0 then
			close()
		else
			begin
				receivestring := System.Text.Encoding.ASCII.GetString(ReceiveBuffer,0,bytesread);
				try
					TCP_Client.BeginReceive(ReceiveBuffer,0, 512,SocketFlags.None, callback_readdata,ari.AsyncState);
					except on ex : Exception
					do
					begin
						statusbar1.Text :='ERROR on read: ' + ex.ToString;
						close();
					end;
				end;
				if receivestring[1] = 'o' then
					begin
						if(convert.ToInt16(receivestring[8]) and 1) = 1 then
							cb_output0.Checked := true
						else
							cb_output0.Checked := false;
						if(convert.ToInt16(receivestring[8]) and 2) = 2 then
							cb_output1.Checked := true
						else
							cb_output1.Checked := false;
					end;
				if receivestring[1] = 'i' then
					begin
						if(convert.ToInt16(receivestring[7]) and 1) = 1 then
							cb_input0.Checked := true
						else
							cb_input0.Checked := false;
						if(convert.ToInt16(receivestring[7]) and 2) = 2 then
							cb_input1.Checked := true
						else
							cb_input1.Checked := false;
					end;
				if receivestring[1] = 'c' then
					begin
						if copy(ReceiveString, 8, 1) = '0' then
							tb_counter0.Text := copy(ReceiveString, 10,length(ReceiveString)-10);
						if copy(ReceiveString, 8, 1) = '1' then
							tb_counter1.Text := copy(ReceiveString, 10,length(ReceiveString)-10);
						if copy(ReceiveString, 8, 1) = ';' then
							begin
								ReceiveString[8] := ' ';
								tb_counter0.Text := copy(ReceiveString, 9, pos(';',ReceiveString)-9);
								tb_counter1.Text := copy(ReceiveString,pos(';',ReceiveString)+1,length(ReceiveString)-pos(';',ReceiveString)-1);
							end;
					end;
			end;
	end;

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.

5. 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.

procedure TWinForm.timer_polling_Tick1(sender: System.Object; e: System.EventArgs);
	begin
		if TCP_Client.Connected then
			begin
				if cb_output_polling.Checked then
					sendcommand('GET/output?PW=' + tb_password.Text + '&');
				if cb_input_polling.Checked then
					sendcommand('GET/input?PW=' + tb_password.Text + '&');
				if cb_counter_polling.Checked then
					sendcommand('GET/counter?PW=' + tb_password.Text + '&');
			end;
	end;

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

procedure TWinForm.tb_interval_TextChanged(sender: System.Object; e: System.EventArgs);
	begin
		timer_polling.Interval := convert.ToInt16(tb_interval.Text);
	end;