如何获取值并使用C＃侦听COM2端口？

Question

I'm working with Dallas Key which is wired on the COM2 port. The dallas Key has a value when it's ON (for example 00 AA BB) and a value when it's removed (for example 00 00 00). How can I ready continuously the value of the COM2 port in order to detect it's change and take actions based on it ( winforms application ).

I've tried to get the value by port name and read it but it says access denied in some cases.

private SerialPort port = new   SerialPort("COM2",9600, Parity.None, 8, StopBits.One); 

   static void Main(string[] args) 
    { 
      SerialPortProgram(); 
    } 

private static void SerialPortProgram() 
    { 
        port.DataReceived += new SerialDataReceivedEventHandler(port_DataReceived); 
        port.Open(); 
        Console.ReadLine();
     } 

    private void port_DataReceived(object sender, SerialDataReceivedEventArgs e) 
    { 
       Console.WriteLine(port.ReadExisting()); 
    } 

I want to listen to the COM2 port value all the time without having a big impact on the application speed, get the value of the COM2 port (my dallas key) when it is ON and detect when it is off and take specific action.

Answer 1

Even though you didn't describe what line actually throws, by reading the documentation i found this nuget

SerialPort.Open Method

Exceptions UnauthorizedAccessException Access is denied to the port.

-or-

The current process, or another process on the system, already has the specified COM port open either by a SerialPort instance or in unmanaged code.

You either don't have permission to open the port, or you already have it open, you need to figure out which one it is and deal with it appropriately

Note : com ports can be a bit fickle if you are using usb to com

Answer 2

The below code works when I write in console (Project is Console Application) but when I changed back to Windows Application and try to write in a label or change a variable value: this doesn't work:

    public Form1()
    {
        InitializeComponent();
        SerialPortProgram();
    }

    private void SerialPortProgram()
    {
        SerialPort mySerialPort = new SerialPort("COM2");

        mySerialPort.BaudRate = 9600;
        mySerialPort.Parity = Parity.None;
        mySerialPort.StopBits = StopBits.One;
        mySerialPort.DataBits = 8;
        mySerialPort.Handshake = Handshake.None;

        mySerialPort.DataReceived += new SerialDataReceivedEventHandler(DataReceivedHandler);
        mySerialPort.Open();
        mySerialPort.Close();
    }

    private void DataReceivedHandler(object sender, SerialDataReceivedEventArgs e)
    {
        SerialPort sp = (SerialPort)sender;
        string indata = sp.ReadExisting();
        switch (ASCIItoHex(indata))
        {
            case "00000113":
                LB_Display.Text = "User 1";
                break;
            case "0000017a":
                LB_Display.Text = "User 2";
                break;
            default:
                LB_Display.Text = "Disconnect";
                break;
        }
    }

    public static string ASCIItoHex(string Value)
    {
        StringBuilder sb = new StringBuilder();
        foreach (byte b in Value)
            sb.Append(string.Format("{0:x2}", b));
        return sb.ToString();
    }