Develop Reference

Continuous serial port read with multiple events

I am new to C# and am looking for some advice on an issue I have been trying to solve in my Windows Form application.
I have an application that needs to continuously read data coming back to the program over a connected serial port. I have buttons that Open and Close the port via the user. I am having trouble configuring the "DataReceived" event handler to read the incoming data and display it in a textbox in the app.
I have been getting this error: "Cross-thread operation not valid: Control 'textBox4' accessed from a thread other than the thread it was created on." I see this is a thread error but I have not been able to figure out my issue.
namespace Program
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
getAvailabePorts();
}
private void getAvailabePorts()
{
String[] ports = SerialPort.GetPortNames();
comboBox1.Items.AddRange(ports);
}
public void button1_Click(object sender, EventArgs e)
{
try
{
if (comboBox1.Text == "" || comboBox2.Text == "")
{
textBox4.Text = "Please select port settings";
}
else
{
serialPort1.PortName = comboBox1.Text;
serialPort1.BaudRate = Convert.ToInt32(comboBox2.Text);
serialPort1.DataReceived += new SerialDataReceivedEventHandler(mySerialPort_DataReceived);
serialPort1.Open();
}
}
catch (UnauthorizedAccessException)
{
textBox4.Text = "Unauthorized Access";
}
public void mySerialPort_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
SerialPort sp = (SerialPort)sender;
textBox4.Text = sp.ReadExisting() + "\n";
}
private void button2_Click(object sender, EventArgs e)
{
serialPort1.Close();
textBox4.Clear();
}
}
}
}

First, welcome.
Before the "big" issue (marshalling data), let me warn you -- serial ports are tricky. For example, your call to "ReadExisting" may not return what you expect -- will return whatever is in the serial port buffer at the time, but more may come in, which will overwrite what is already in your text box. So you may want to append data your text box.
Now the real issue. As a commentor mentioned, you cannot post directly post data from another thread to the UI thread. Without you knowing, the serial port created a new thread to receive data.
You can handle this directly by modifying your receiver code as follows:
public void mySerialPort_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
SerialPort sp = (SerialPort) sender;
var dataRcvd = sp.ReadExisting();
object[] dataArray = new object[1];
dataArray[0] = dataRcvd;
BeginInvoke( new postDataDelegate( postData), dataArray );
}
private delegate void postDataDelegate( string d );
private void postData( string d)
{
textBox4.Text = d;
}
This will "marshall" the data to the UI thread so it can be used. There are many ways this can be done (and, many differences between how it is done in WPF vs. Winforms, so watch out for that). I hope this illustrates the point.
Another aside -- no need ot make the DataReceived method public -- it will work fine private.

C# COM port receive info

I have a piece of code like this:
public class SerialPortListener
{
#region Properties
public SerialPort _Port { get; set; }
public event EventHandler<SerialDataEventArgs> DataReceived;
#endregion
public void Start()
{
Close();
//todo: get attached COM names...
List<string> names = SerialPort.GetPortNames().ToList();
// todo: for testing, let's pick first...
string name = names.FirstOrDefault();
if (string.IsNullOrEmpty(name))
return; // todo: throw error that no devices are attached...
_Port = new SerialPort(name);
_Port.DataReceived += new SerialDataReceivedEventHandler(DataReceivedHandler);
_Port.Open();
}
private void DataReceivedHandler(object sender, SerialDataReceivedEventArgs e)
{
SerialPort port = (SerialPort)sender;
string data = port.ReadExisting();
if (DataReceived != null)
DataReceived(this, new SerialDataEventArgs(data));
}
public void Close()
{
if (_Port != null && _Port.IsOpen)
_Port.Close();
}
}
public class SerialDataEventArgs : EventArgs
{
public SerialDataEventArgs(string data)
{
Data = data;
}
/// <summary>
/// Byte array containing data from serial port
/// </summary>
public string Data;
}
where com port name is "COM1", and I have connected a handheld barcode scanner.
I noticed that it works only when I put a breakpoint on _Port.Open() and then step over it after which I press continue in the debugger. Then scanning works and DataReceivedHandler is called.
Otherwise it doesn't work and scanner also doesn't get a good read beep.
I Tested scanner in the application I got from here ,where it works fine every time.
My question is why doesn't it work every time like in example app and what can be done differently to make it work.

When using COM ports, it is important to close them after use.
Otherwise they will remain unavailable for opening again until they are closed.
Therefore, when debugging, it is important to not simply hit "stop debugging" but have some cleanup code running in all circumstances that will gracefully close the port.
I'd also recommend adding an unhandled exception handler in the App that makes sure the port will be closed before exiting the Application in case of an unexpected error.
Also, the documentation of the "Open" method states under "Remarks":
The best practice for any application is to wait for some amount of time after calling the Close method before attempting to call the Open method, as the port may not be closed instantly.

C# GUI refresh and async serial port communication

I'm trying to create an application which communicates with hardware via serial port and reports the results to the gui.
Currently moving through GUI is made by KeyEvents which trigger the drawing of the next "page" of GUI. However at one step (after the key is pressed) I need to draw new page and send few commands via serial port.
The command sending is done via :
port.Write(data, 0, data.Length);
I then wait for the answer by waiting for DataReceivedHandler to trigger - it just pins out that there is data awaiting and data is being processed in another method.
At first I just put sending & receiving command in the function drawing the page after the "draw parts" however it made it stuck - the data was being transfered, but the page wasn't drawn - it was frozen.
Then I made an async method :
private async void SendData()
{
await Task.Run(() => serialClass.SendAndReceive(command));
// process reply etc.
}
Which is used like that :
public void LoadPage()
{
image = Image.FromFile(path);
//do some stuff on image using Graphics, adding texts etc.
picturebox1.Image = image;
SendData();
}
It works fine, however I need to "reload" the page (to call again LoadPage). If I do it inside the async method like this :
private async void SendData()
{
await Task.Run(() => serialClass.SendAndReceive(command));
// process reply etc.
LoadPage();
}
Then obviously the image won't be refreshed, though the data will be send via serial port. Is it possible to somehow check if async function was finished and trigger an event where I could reload the page?
So far I've tried using the BackGroundWorker Work Complete and Property Change. The data was send again, but the image wasn't reloaded. Any idea how I can achieve that?
Thanks in advance for the help,
Best regards

You need to use a state machine and delegates to achieve what you are trying to do. See the code below, I recommend doing all this in a separate thread other then Main. You keep track of the state you're in, and when you get a response you parse it with the correct callback function and if it is what you are expecting you move onto the next send command state.
private delegate void CallbackFunction(String Response); //our generic Delegate
private CallbackFunction CallbackResponse; //instantiate our delegate
private StateMachine currentState = StateMachine.Waiting;
SerialPort sp; //our serial port
private enum StateMachine
{
Waiting,
SendCmd1,
Cmd1Response,
SendCmd2,
Cmd2Response,
Error
}
private void do_State_Machine()
{
switch (StateMachine)
{
case StateMachine.Waiting:
//do nothing
break;
case StateMachine.SendCmd1:
CallbackResponse = Cmd1Response; //set our delegate to the first response
sp.Write("Send first command1"); //send our command through the serial port
currentState = StateMachine.Cmd1Response; //change to cmd1 response state
break;
case StateMachine.Cmd1Response:
//waiting for a response....you can put a timeout here
break;
case StateMachine.SendCmd2:
CallbackResponse = Cmd2Response; //set our delegate to the second response
sp.Write("Send command2"); //send our command through the serial port
currentState = StateMachine.Cmd2Response; //change to cmd1 response state
break;
case StateMachine.Cmd2Response:
//waiting for a response....you can put a timeout here
break;
case StateMachine.Error:
//error occurred do something
break;
}
}
private void Cmd1Response(string s)
{
//Parse the string, make sure its what you expect
//if it is, then set the next state to run the next command
if(s.contains("expected"))
{
currentState = StateMachine.SendCmd2;
}
else
{
currentState = StateMachine.Error;
}
}
private void Cmd2Response(string s)
{
//Parse the string, make sure its what you expect
//if it is, then set the next state to run the next command
if(s.contains("expected"))
{
currentState = StateMachine.Waiting;
backgroundWorker1.CancelAsync();
}
else
{
currentState = StateMachine.Error;
}
}
//In my case, I build a string builder until I get a carriage return or a colon character. This tells me
//I got all the characters I want for the response. Now we call my delegate which calls the correct response
//function. The datareceived event can fire mid response, so you need someway to know when you have the whole
//message.
private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
{
string CurrentLine = "";
string Data = serialPortSensor.ReadExisting();
Data.Replace("\n", "");
foreach (char c in Data)
{
if (c == '\r' || c == ':')
{
sb.Append(c);
CurrentLine = sb.ToString();
sb.Clear();
CallbackResponse(CurrentLine); //calls our correct response function depending on the current delegate assigned
}
else
{
sb.Append(c);
}
}
}
I would put this in a background worker, and when you press a button or something you can set the current state to SendCmd1.
Button press
private void buttonStart_Click(object sender, EventArgs e)
{
if(!backgroundWorker1.IsBusy)
{
currentState = StateMachine.SendCmd1;
backgroundWorker1.RunWorkerAsync();
}
}
Background worker do work event
private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
{
while (true)
{
if (backgroundWorker1.CancellationPending)
break;
do_State_Machine();
Thread.Sleep(100);
}
}
edit: you can use invoke to update the GUI from your background worker thread.
this.Invoke((MethodInvoker)delegate
{
image = Image.FromFile(path);
//do some stuff on image using Graphics, adding texts etc.
picturebox1.Image = image;
});

How to display data received from serial port in a textbox without the text disappearing in Visual Studio C#?

So, I'm trying to develop a simple application in visual C# which gets data from serial port and displays it in a textbox (to monitor temperature). I'm acquiring and displaying the data successfully, using the DataReceived event to update a global string variable and a timer to update the text field on my text box, as shown:
private void port_DataReceived_1(object sender, SerialDataReceivedEventArgs e)
{
try
{
globalVar.updateTemp = port.ReadLine(); //This is my global string
}
catch (IOException)
{
}
catch (InvalidOperationException)
{
}
catch (TimeoutException)
{
}
}
private void timer1_Tick(object sender, EventArgs e)
{
tempDisplayBox.Text = globalVar.updateTemp; //This is my textbox updating
}
The only issue I have is that the value shown in the textbox keeps flashing, making it hard to read. My timer is set to trigger every 10 ms (which should be fast enough, right?). Is there any way to make it more stable? I realize this may be a newb question, but to be fair I am a newb :) Any help is appreciated! Thanks!

Do you really need it updating every 10ms? What about every 500 ms or if not that then 100ms. 100ms will require your update method run 10 times less and therefore update 10 times less. The flickering you are expiriencing is due to the refresh speed. You could create custom method which will only update the temp only when target Label or textBox value is different than source port. But that will only sort the flickering when temp is steady, when temp will start vary it will bring back the flickering. Good luck ;-)
UPDATE
Hi I tried to reproduce the conditions and could not make my textbox nor Label flash. The way I tested it was by assigning int ntick = 0; and then increment the ++ntick; inside of the timer_tick method. The results didn't make any of the controls flash and were updated even every milisecond at some point. I also tried string.Format to put some load on the method. Is your app responsive?

The trick is to use double buffering. This way the operating system will redraw the Control off-screen, and only show the control when it is fully redrawn.
I have had the same problem, and solved it by extending the TextBox control like this:
public FastLogBox()
{
InitializeComponent();
_logBoxText = new StringBuilder(150000);
timer1.Interval = 20;
timer1.Tick += timer1_Tick;
timer1.Start();
SetStyle(ControlStyles.DoubleBuffer, true);
}
void timer1_Tick(object sender, EventArgs e)
{
if (_timeToClear)
{
_logBoxText.Clear();
_timeToClear = false;
}
if (_logQueue.Count <= 0) return;
while (!_logQueue.IsEmpty)
{
string element;
if (!_logQueue.TryDequeue(out element)) continue;
{
_logBoxText.Insert(0, element + "\r\n");
}
}
if (_logBoxText.Length > 150000)
{
_logBoxText.Remove(150000, _logBoxText.Length - 150001);
}
Text = _logBoxText.ToString();
}
public new void Clear()
{
_timeToClear = true;
while (!_logQueue.IsEmpty)
{
string element;
_logQueue.TryDequeue(out element);
}
}
public void AddToQueue(string message)
{
_logQueue.Enqueue(message);
}
}
I also use a timer and a concurrentQueue to avoid using Invoke to update the control from another thread. I also use a StringBuilder to prepare the string before putting it into the TextBox. StringBuilder is faster when building larger strings.

You can use ReadExisting() to read the whole data at a time.
You need to handle DataReceived Event of SerialPort
serialPort1.ReadExisting();
Sample:
private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
{
String myData=serialPort1.ReadExisting();
}
Example Code: Here i would like to show you the code to Read Data(RFID Tag Code which is basically of length 12)
String macid = "";
private void DoWork()
{
Invoke(
new SetTextDeleg(machineExe ),
new object[] { macid });
macid = "";
}
private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
{
string str1;
macid += serialPort1.ReadExisting();
if (macid.Length == 12)
{
macid = macid.Substring(0, 10);
Thread t = new Thread(new ThreadStart(DoWork));
t.Start();
}
}
public void machineExe(string text)
{
TextBox1.Text=text;
}

Thank you so much for the answers! I found a way to work around this issue:
Instead of replacing the contents of my textbox by rewriting the TextBox.Text property - which, as HenningNT implied, refreshes the control and causes the flickering - I'm now using the TextBox.AppendText method. Though, as I want to display only one line of data at a time, I use the textbox in multiline mode and the Environment.NewLine to jump to a new line before appending the text. As for the method of updating, I've gone back to using the timer because with the invoke method was crashing my application when I close the form, for some reason. Also, enabling double buffering didn't do me much good, although I guess I was doing it wrong... It still flickers a bit, but it's much better now :) I know this is not really a perfect solution (much more of a workaround), so I'll keep looking for it. If I find it, I'll be sure to update it here ;) My code:
private void timer1_Tick(object sender, EventArgs e) //Timer to update textbox
{
if (tempDisplayBox.Text != globalVar.updateTemp) //Only update if temperature is different
{
try
{
tempDisplayBox.AppendText(Environment.NewLine);
tempDisplayBox.AppendText(globalVar.updateTemp);
}
catch (NullReferenceException)
{
}
}
}

UI Forms events block my other STOCK TICKER API events - how can I prevent this?

I have an API (dll) that collects stock ticks via an event mechanism. Such as below:
...
using MT4API;
public partial class Blue : Form
{
...
public Blue()
{
...
string symbol = "GBPUSD";
MT4DDE dde = new MT4DDE("");
dde.OnQuote += new System.EventHandler<QuoteEventArgs>(MT_OnQuote);
dde.Connect();
dde.Subscribe(symbol);
....
The idea is that on each chart tick I get an event. here is the event handler code:
private static void MT_OnQuote(object sender, QuoteEventArgs args)
{
GlobalClass.Ask = args.Ask;
GlobalClass.Bid = args.Bid;
// I have back ground worker code that updatestables from the global class
}
This all works fine. So long as I do not touch any other buttons on the form UI. As soon as I click a button on the form of the UI... I no longer receive events from my API, the UI application functions normally, but with no data from the API.
Why do events from the UI stop any further events coming from the API event?
Any idea whats going on here? Or suggestions how to design this?

Does the same problem occur if you comment out your code that updates the tables from the global object? and if you comment out the background worker?
It would be a good idea to distinguish if the event stops being fired just after you press some button on the UI, or if it stops being fired only after some line of code you wrote is being executed.
In order to be able to help you, we would need to know how the event on the MT4DDE class is triggered.
If you have the code for this class, posting it would help.
If you don't you may want to use a tool such as Reflector to decompile the assembly into C# and see what the MT4DDE class is doing that might cause it to stop invoking the event.
In addition, if you are doing anything related to background threads, or if you're doing anything unusual with your application's main message loop, it would be a good idea to mention it here.

I have tried to use the invoke command, it works, but after a few events it stops...here is the code isolated:
using MT4API;
namespace WindowsFormsApplication1
{
public delegate void UpdateTextCallback(double ask, double bid);
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
string symbol = "GBPUSD";
MT4DDE dde = new MT4DDE("");
dde.OnQuote += new EventHandler<QuoteEventArgs>(MT_OnQuote);
dde.Connect();
dde.Subscribe(symbol);
}
private void updateTickDisplay(double ask, double bid)
{
textBox1.Text = ask.ToString();
textBox2.Text = bid.ToString();
}
private void button1_Click(object sender, EventArgs e)
{
this.Close();
}
private void MT_OnQuote(object sender, QuoteEventArgs args)
{
BeginInvoke(new UpdateTextCallback(this.updateTickDisplay),
new object[] { args.Ask, args.Bid });
}
private void textBox1_TextChanged(object sender, EventArgs e)
{
textBox3.Text = textBox1.Text;
}
}
}
The only difference from the real code is that I am using a data grid....as opposed to a text field. But it is clear that the UI blocks somehow the new events. It is strange that I get about 5 to 10 events and then it just stops. Strange. Any ideas on a differnet design?