Using worker thread to read from serial port

Question

Hello

First of all I have to say that I never worked with threads, this will be my first multi-thread application. This is my problem:
I have a card reader connected to a serial port, and I made an application that reads the cards serial number and with some other informations stores it into a database. However I have to use MessageBox to ask if user wants to read from a new card - this is extremely unpractical when working with a large number of cards. I tired to put the reading part into a loop, but that lock's all other controls, and I can't stop it once I'm done. I asked around a bit and everybody told me that threads are the right way to solve this problem. I did some reading and if I got it correct it should be possible to make 2 threads - one worker thread to read from the serial port and store the data, and the main (basic thread) one to stop the worker thread when I want to. This is my idea:
- User clicks a button that starts the worker.
- Worker reads from the serial port reader, and stores the data (like I said I actually have this part solved, I just need to make it more practical)
- All of the data that is read is automatically displayed in a DataGridView control (this part is also solved)
- User can stop the worker by clicking on another button.
Can you give me a link to some tutorial that could help me solve this problem, or if you can help me in any other way, I would be most thankful.

Again I am a complete beginner to multi-threading, so please bare that in mind when answering.
Thanks

Vulpes · Answer

OK. I'm back with some suggested code: // in declaration area SerialPort port = new SerialPort(); // in form1_load method port.PortName = COM4; port.BaudRate = 9600; port.Parity = Parity.None; port.StopBits = StopBits.One; // in button1_Click to connect if(!port.IsOpen) { port.DataReceived += port_DataReceived; port.Open(); } // in button2_Click to disconnect if(port.IsOpen) { port.DataReceived -= port_DataReceived; port.Close(); } // add this handler private void port_DataReceived(object sender System.IO.Ports.SerialDataReceivedEventArgs e) { // read all bytes in input buffer string data = port.ReadExisting(); // assign to textbox by marshalling to UI thread this.Invoke(new MethodInvoker(delegate() { textBox1.Text = data; // add code to store data permanently })); }

prabhat s · Answer

Thank you Vulpes . that solved my problems anyway. serialPort1.DataReceived -=serialPort1_DataReceived);

Neven Draskovic · Answer

Excellent your code worked perfectly when I applied it to my test application. Now I will try to apply it to the real application but I think that should be no problem. Thank you very much this is great.

Neven Draskovic · Answer

Ok thank you very much - I'll keep trying to work something out but if you have the time it would be great if you could write some code or something.

Vulpes · Answer

Yes the problem is that you're not using the DataReceived handler and need to use it so that when data is received the handler is called on a separate thread and doesn't lock up the UI. However this isn't a totally straightforward matter as you still need to communicate results back to the UI thread. I have to go out now for an hour or so but I'll try and come up with some code when I get back.

Neven Draskovic · Answer

This is the code I'm using to communicate with serial port: SerialPort port = new SerialPort(); //in declaration area port.PortName = COM4; port.BaudRate = 9600; //in form1_load method port.Parity = Parity.None; port.StopBits = StopBits.One; port.Open(); //in button1_click method textBox1.Text = port.ReadLine(); Now you see my problem the button1 should be clicked for every entry that I want to make and that is completely unpractical. I've tried to do this: while(bool_varable == true) { textBox1.Text = port.ReadLine(); } And then use the button2 to change the bool_variable to false but as long as the while loop is running I cant click anything on the form (I've tried using Application.DoEvents but that was only semi successful). I know that -= is not an error I was referring to port_DataReceived on the right side of the expression - the compiler keeps saying that it does not exist in current context.

Vulpes · Answer

The '-=' is not a typing error but is C#'s syntax for disconnecting an eventhandler which was connected using the '+=' syntax. The names I used are the ones typically generated by Visual Studio when you add a SerialPort component via the designer. The DataReceived eventhandler looks like this: private void serialPort1_DataReceived(object sender System.IO.Ports.SerialDataReceivedEventArgs e) { // your code } and the line which is added to the InitializeComponent() method look like this: this.serialPort1.DataReceived += new System.IO.Ports.SerialDataReceivedEventHandler(this.serialPort1_DataReceived); though it can be abbreviated to just this: serialPort1.DataReceived += serialPort1_DataReceived; Are you in fact using the DataReceived handler in your program or are you detecting when bytes are available to be read using other means?

Neven Draskovic · Answer

When I write your code in button_Click handler (I suppose that I should put it in the cancel button) I get the error The event ... can only appear on the left side of += or -= (also I changed the _ on the right side to . was this a typing error or did you put it intentionally? If I put the _ the compiler says that the name does not exist in current context). I don't know does this make any difference - I'm using ReadLine and ReadTo methods to read from serial port Thanks again

Vulpes · Answer

Well normally I'd suggest you use a BackgroundWorker but the SerialPort.DataReceived event is actually called on a secondary thread in any case. You can disconnect it at any time by placing a line such as this in a button_Click handler: serialPort1.DataReceived -= serialPort1_DataReceived;