How to pass a Variable to Lambda Expression

Question

I was just starting to use C# last week and tried to create a simple serial monitor program. I want my program to read data from serialport continuously while displaying those data in the Form Application at the same time. I use the code from here as reference https://github.com/ahelsayd/Serial-Lab

I use the same BeginInvoke() function. However I can not pass the variable that I want to write.

This is the original code

private void rx_data_event(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
        {
            if (mySerial.IsOpen)
            {
                try
                {
                    //=====Only this part is different=======================
                    int dataLength = mySerial.BytesToRead;
                    byte[] dataReceived = new byte[dataLength];
                    int nbytes = mySerial.Read(dataReceived, 0, dataLength);
                    if (nbytes == 0) return;
                    //=====Only this part is different=======================

                    this.BeginInvoke((Action)(() =>
                    {
                        data = System.Text.Encoding.Default.GetString(dataReceived);

                        if (!backgroundWorker1.IsBusy)
                        {
                            backgroundWorker1.RunWorkerAsync();
                        }
                    }));

                }
                catch { alert("Can't read form  " + mySerial.PortName + " port it might be opennd in another program"); }
            }
        }


//And then update the UI
private void update_rxtextarea_event(object sender, DoWorkEventArgs e)
        {
            this.BeginInvoke((Action)(() =>
            {
                if (rx_textarea.Lines.Count() > 5000)
                    rx_textarea.ResetText();
                rx_textarea.AppendText("[RX]> " + data);
            }));
        }

This code can read the Serialport and Write into the Form simultaneously. However, it does not receive all data from the serialport. So I modified the code to write the data into a buffer first until all data is received.

The modified code

private void rx_data_event(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
        {
            if (mySerial.IsOpen)
            {
                try
                {
                    //=====Only this part is different=======================
                    string Data = mySerial.ReadExisting();
                    serialBuffer.Append(Data);

                    string bufferString = serialBuffer.ToString();
                    int index = -1;
                    do
                    {
                        index = bufferString.IndexOf(terminationSequence);
                        if (index > -1)
                        {
                            string message = bufferString.Substring(0, index);
                            bufferString = bufferString.Remove(0, index + terminationSequence.Length);
                        }
                    }
                    while (index > -1); 
                    serialBuffer = new StringBuilder(bufferString);
                    byte[] bytes = new byte[30];
                    if (serialBuffer.Length == 15) {
                        Console.WriteLine("data:" + serialBuffer);
                        bytes = Encoding.ASCII.GetBytes(serialBuffer.ToString());
                     }
                    //=====Only this part is different=======================

                    this.BeginInvoke((Action)(() =>
                    {
                        data = Encoding.ASCII.GetString(bytes);

                        if (!backgroundWorker1.IsBusy)
                        {
                            backgroundWorker1.RunWorkerAsync();
                        }
                    }));

                }
                catch { alert("Can't read form  " + mySerial.PortName + " port it might be opennd in another program"); }
            }
        }

The problem is in the Form application the value of bytes is always null although when I checked by writing the output value to console window I can see the value of bytes updated.

I am very confused why the variable dataReceived value can be accessed by BeginInvoke while the variable bytes keep having null value. Is there something that I've missed that causing the value not get updated?

Answer 1

So I wasn't able to do it yesterday, but I promised the OP I would write something in an answer related to a comment of mine. From what I understand he/she is trying to update something in a Form based on received data from a serial port. Here's how I do it:

First off you need to declare a delegate and an event (which is basically a list of delegates):

public delegate void Data_Received_EventHandler(object sender, Data_Received_EventArgs e);
public event Data_Received_EventHandler Data_Received;

These are used to substitute the original "data received" event and event args from the serial port.

I usually define the Data_Received_EventArgs type as something based of an array of bytes, for simplicity:

public class Data_Received_EventArgs : EventArgs
{
    public byte[] data;

    internal Data_Received_EventArgs(int length)
    {
        data = new byte[length];
    }
}

Then, in the original data reception event (let's say your serial port is called serialPort1):

private void serialPort1_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
    // check how many bytes you need to read:
    int bytesToRead = serialPort1.BytesToRead;

    // declare your arguments for the event based on that number of bytes (check the Data_Received_EventArgs constructor):
    Data_Received_EventArgs args = new Data_Received_EventArgs(bytesToRead);

    // copy the bytes from your serial port into the arguments:
    for (int i = 0; i < bytesToRead; i++)
        args.data[i] = (byte)serialPort1.ReadByte();

    // verify if there are subscribers to the event (list not empty) and fire your event using BeginInvoke:
    if (Data_Received != null)
        BeginInvoke((MethodInvoker)delegate () { Data_Received(this, args); });
}

What we now have is an event which is guaranteed to execute its handlers on the UI thread. To use it, you can subscribe to the event like so:

Data_Received += My_Data_Received_Handler;

Your handler should have the same signature as the delegate we declared in the first line of code (should be void and have specified parameters):

private void My_Data_Received_Handler(object sender, Data_Received_EventArgs e)
{
    // read bytes from the arguments as you normally would from an array and do whatever e.g.:
    some_Label.Text = e.data[0].ToString(); // without worrying about crossthreading
}

I know this is not the answer the OP wanted, but I hope it helps in simplifying what he/she was trying to do in the first place.