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Serial COM read returns null [duplicate]

I am developing program which need to interact with COM ports.
By learning from this Q&A: .NET SerialPort DataReceived event not firing, I make my code like that.
namespace ConsoleApplication1
{
class Program
{
static SerialPort ComPort;
public static void OnSerialDataReceived(object sender, SerialDataReceivedEventArgs args)
{
string data = ComPort.ReadExisting();
Console.Write(data.Replace("\r", "\n"));
}
static void Main(string[] args)
{
string port = "COM4";
int baud = 9600;
if (args.Length >= 1)
{
port = args[0];
}
if (args.Length >= 2)
{
baud = int.Parse(args[1]);
}
InitializeComPort(port, baud);
string text;
do
{
String[] mystring = System.IO.Ports.SerialPort.GetPortNames();
text = Console.ReadLine();
int STX = 0x2;
int ETX = 0x3;
ComPort.Write(Char.ConvertFromUtf32(STX) + text + Char.ConvertFromUtf32(ETX));
} while (text.ToLower() != "q");
}
private static void InitializeComPort(string port, int baud)
{
ComPort = new SerialPort(port, baud);
ComPort.PortName = port;
ComPort.BaudRate = baud;
ComPort.Parity = Parity.None;
ComPort.StopBits = StopBits.One;
ComPort.DataBits = 8;
ComPort.ReceivedBytesThreshold = 9;
ComPort.RtsEnable = true;
ComPort.DtrEnable = true;
ComPort.Handshake = System.IO.Ports.Handshake.XOnXOff;
ComPort.DataReceived += OnSerialDataReceived;
OpenPort(ComPort);
}
public static void OpenPort(SerialPort ComPort)
{
try
{
if (!ComPort.IsOpen)
{
ComPort.Open();
}
}
catch (Exception e)
{
throw e;
}
}
}
}
My problem is DataReceived event never gets fired.
My program specifications are:
Just .net console programming
I use VSPE from http://www.eterlogic.com
My computer has COM1 and COM2 ports already.
I created COM2 and COM4 by using VSPE.
I get output result from mystring array (COM1, COM2, COM3, COM4)
But I still don't know why DataReceived event is not fired.
Updated
Unfortunately, I still could not make to fire DataReceived event in any way.
So, I created new project by hoping that I will face a way to solve.
At that new project [just console application], I created a class...
public class MyTest
{
public SerialPort SPCOM4;
public MyTest()
{
SPCOM4 = new SerialPort();
if(this.SerialPortOpen(SPCOM4, "4"))
{
this.SendToPort(SPCOM4, "com test...");
}
}
private bool SerialPortOpen(System.IO.Ports.SerialPort objCom, string portName)
{
bool blnOpenStatus = false;
try
{
objCom.PortName = "COM" + portName;
objCom.BaudRate = 9600;
objCom.DataBits = 8;
int SerParity = 2;
int SerStop = 0;
switch (SerParity)
{
case 0:
objCom.Parity = System.IO.Ports.Parity.Even;
break;
case 1:
objCom.Parity = System.IO.Ports.Parity.Odd;
break;
case 2:
objCom.Parity = System.IO.Ports.Parity.None;
break;
case 3:
objCom.Parity = System.IO.Ports.Parity.Mark;
break;
}
switch (SerStop)
{
case 0:
objCom.StopBits = System.IO.Ports.StopBits.One;
break;
case 1:
objCom.StopBits = System.IO.Ports.StopBits.Two;
break;
}
objCom.RtsEnable = false;
objCom.DtrEnable = false;
objCom.Handshake = System.IO.Ports.Handshake.XOnXOff;
objCom.Open();
blnOpenStatus = true;
}
catch (Exception ex)
{
throw ex;
}
return blnOpenStatus;
}
private bool SendToPort(System.IO.Ports.SerialPort objCom, string strText)
{
try
{
int STX = 0x2;
int ETX = 0x3;
if (objCom.IsOpen && strText != "")
{
objCom.Write(Char.ConvertFromUtf32(STX) + strText + Char.ConvertFromUtf32(ETX));
}
}
catch (Exception ex)
{
throw ex;
}
return true;
}
}
I am not sure that I face good luck or bad luck because this new class could make fire DataReceived event which is from older console application that is still running. It is miracle to me which I have no idea how this happen.
Let me tell you more detail so that you could give me suggestion for better way.
Finally I created 2 console projects.
First project is the class which I posted as a question yesterday.
Second project is the class called MyTest which could make fire DataReceived event from First project, at the same time when two of the project is running.
Could anyone give me suggestions on how could I combine these two projects as a single project?

ComPort.Handshake = Handshake.None;
The problem is not that the DataReceived event doesn't fire, the problem is that the serial port isn't receiving any data. There are very, very few serial devices that use no handshaking at all. If you set it to None then the driver won't turn on the DTR (Data Terminal Ready) and RTS (Request To Send) signals. Which a serial port device interprets as "the machine is turned off (DTR)" or "the machine isn't ready to receive data (RTS)". So it won't send anything and your DataReceived event won't fire.
If you really want None then set the DTREnable and RTSEnable properties to true. But it is likely you want HandShake.RequestToSend since the device appears to be paying attention to the handshake signals.
If you still have trouble then use another serial port program like Putty or HyperTerminal to ensure the connection and communication parameters are good and the device is responsive. SysInternals' PortMon utility gives a low-level view of the driver interaction so you can compare good vs bad.

I have never worked with VSPE so I'm not sure if that causes the problem. I have worked with a COM port before and I looked up my code. The only main difference is the way you declare the event. You have:
ComPort.DataReceived += OnSerialDataReceived;
I have it like this:
ComPort.DataReceived += new SerialDataReceivedEventHandler(OnSerialDataReceived);
OnSerialDataReceived is your eventhandler. I'm not sure if this will make any difference, but you can try it. I hope this helps!

I had a quite similar problem. In a graphical application (C# win form) I had a class which encapsulate a SerialPort component. The DataReceived event was firing only one time, but then any following data received didn't fire any event. I solved the problem by calling the Close method in my principal form Closed event function.
No idea of why that changes anything, but now it's working.

Arduino and C# Serial Port "Crash"

I am trying to create a communication between an Arduino Leonardo and C#.
Just now, the Arduino's software sends a simple message (in loop) on the serial port:
void setup() {
Serial.begin(9600);
analogReference(INTERNAL);
}
void loop() {
Serial.println("test");
delay(500);
}
C# try only to read these messages and print them on the shell:
public class Program
{
private SerialPort mySerialPort;
static void Main(string[] args)
{
Program p = new Program();
Console.WriteLine("PORTS: " + String.Join(" ", p.getSerialPortsList())+ ", enter to start.");
Console.Read();
p.SerialRead("COM6");
}
public String[] getSerialPortsList()
{
string[] ports = SerialPort.GetPortNames();
return ports;
}
public void SerialRead(String com)
{
mySerialPort = new SerialPort(com, 9600, Parity.None, 8, StopBits.One);
Console.Read();
Console.WriteLine("Incoming Data:");
SerialRead sr = new SerialRead();
Thread rs = new Thread(sr.StartRead);
sr.SetMySerialPort(mySerialPort);
rs.Start();
while (!rs.IsAlive);
Console.Read();
sr.SetSuspendThread(true);
rs.Join();
}
}
public class SerialRead
{
private Boolean suspendThread = false;
SerialPort mySerialPort;
public void StartRead()
{
mySerialPort.Open();
Thread.Sleep(500);
int i = 0;
while (!suspendThread)
{
i++;
Console.WriteLine(i + ": " + mySerialPort.ReadLine());
Thread.Sleep(500);
}
}
public void SetMySerialPort(SerialPort mysp){ mySerialPort = mysp; }
public void SetSuspendThread(Boolean a){ suspendThread = a; }
}
The output of this C# software depends. If I use the serial monitor on the Arduino IDE, then I receive the string's stream correctly (one each 500ms).
Otherwise, the C# software freezes. Sometimes, I receive a couple of strings as we can see this figure; but almost all time, the software does not give any string, as we can see here. After that the software freezes (thus, if I press enter the shell does not response).
Can you suggest a solution in order to get a fluent flow of string, and -as a consequence- read each message sent by Arduino on the serial port?
I am using Window 10 x64 as OS and the COM6 (it is an USB 2.0).

I found the solution and I share it in order to help people with the same problem.
C# does not activate as default the RTS and the DTR serial port.
Thus, adding
mySerialPort.DtrEnable = true;
mySerialPort.RtsEnable = true;
after the serial port declaration, everything works fine.

This is a really good example:
Serial Port Polling and Data handling
The Serial Port got an event called DataRecived, so you dont have to sleep your thread.
Something like this:
serialPort.DataReceived +=SerialPortDataReceived;
private void SerialPortDataReceived(object sender, SerialDataReceivedEventArgs e)
{
Console.WriteLine(serialPort.ReadLine());
}

Why is this PortName deemed nonexistent?

I'm trying to refactor/update some legacy serial comm code. I've got this:
private SerialPort cereal;
private String receivedData;
private FileXferLegacy()
{
cereal = new SerialPort("COM1", 9600);
cereal.PortName = "7727";
cereal.DataReceived += new SerialDataReceivedEventHandler(port_DataReceived);
// Is this just as well, as the elided part is grayed out above?: cereal.DataReceived += port_DataReceived;
}
...but am getting the err msg "The port '7727:' does not exist" when I try to connect and send a ping:
public void SendDataContentsAsXML(string destinationPath, string XMLData)
{
byte[] stuff;
ExceptionLoggingService.Instance.WriteLog("Reached FileXferLegacy.SendDataContentsAsXML"); // <= This is written to the log file
cereal.Open();
stuff = System.Text.UTF8Encoding.UTF8.GetBytes("PING" + "\n");
cereal.Write(stuff, 0, stuff.Length);
stuff = System.Text.UTF8Encoding.UTF8.GetBytes(XMLData + "\n");
cereal.Write(stuff, 0, stuff.Length);
}
7727 is the same port that is successfully used in the legacy app.
I do see that there is a colon appended, and wonder if that is the problem - why is it seeing "7727:" instead of plain old "7727", and how can I disabuse it of the notion of having an appended colon if that is indeed a problem?

Because PortName refers to the serial port name, not a port number. In your code you're creating your SerialPort object
cereal = new SerialPort("COM1", 9600);
So COM1 is already being assigned to PortName. Your next statement is just overriding it unnecessarily and incorrectly.

Loop get paused/diactivated inside catch() block

I am trying to send AT commands to COM ports, so I can find the GSM dongle. Below is the code
public bool findGsmModem()
{
bool sendStatus = false;
//Get all the available ports
string[] serialPorts = SerialPort.GetPortNames();
for (int i = 0; i < serialPorts.Length; i++)
{
Console.WriteLine(serialPorts[i]);
}
//Iterate through all the ports sending AT commands to find a modem
for (int i = 0; i < 1; i++)
{
try
{
//port.PortName = serialPorts[i].Trim();
port.PortName = "COM7";
openPort();
string res = ATCommandCaller("AT", 300,"Unable to connect to the phone"); //Connecting to the phone
//res = ATCommandCaller("AT+CMGF=1", 300); //Setting the message Format
sendStatus = true;
break;
}
catch (System.InvalidOperationException ex)
{
//port.PortName = null;
port.Close();
autoInitializer();
//port = new SerialPort();
continue;
//throw ex;
}
}
return sendStatus;
}
Here is how I call this method inside another class
if (sms.findGsmModem())
{
MessageBox.Show("Modem Found: " + sms.getPortName());
}
else
{
MessageBox.Show("No modem found");
}
OK, now in the findGsmModem() method if I use port.PortName = "COM5"; the above second code works successfully and display the message. That is because the Modem is actually in COM5 and the value is hard coded, so the statement do not reach the catch() block.
But, if I use port.PortName = serialPorts[i].Trim(); or port.PortName = serialPorts[i]; then it seems like nothing is happening instead of printing the port names (inside findGsmModem()). Following ports are being printed
COM1
COM2
COM8
COM9
COM5
COM4
COM3
As you can see, the COM5, the port where the gms modem actually exists is in the 5th element of the array, so findGsmModem() calls catch() part before it access the COM5.
I do believe I am not getting anything when port.PortName = serialPorts[i].Trim() is used because it goes to the catch() part and something terrible happens there.
Any idea?
Here is the openPort() method
public void openPort()
{
try
{
port.DataReceived += new SerialDataReceivedEventHandler(port_DataReceived);
if (!port.IsOpen)
{
port.Open();
}
port.RtsEnable = true;
port.DtrEnable = true;
}
catch (Exception ex)
{
throw ex;
}
}
EDIT
Here is the most weirdest part. I just noticed the catch() block never get reached when the loop is called! I tried ex.Message to print the stack trace, and it didn't print anything!

catch (Exception ex)
This is the trouble with catch-em-all exception handling. You are getting an InvalidOperationException because you change the PortName property on a opened port. That's a bug in your code, nothing actually went wrong with the serial port.
You'll need to call the Close() method if you find out that it port is not connected to the GSM modem.
Then you can't call Open() again on that same SerialPort instance, it takes time for internal worker thread to shut down. Best thing to do is to create a new instance of SerialPort instead of trying to keep using the same one repeatedly.

C# check if a COM (Serial) port is already open

Is there an easy way of programmatically checking if a serial COM port is already open/being used?
Normally I would use:
try
{
// open port
}
catch (Exception ex)
{
// handle the exception
}
However, I would like to programatically check so I can attempt to use another COM port or some such.

I needed something similar some time ago, to search for a device.
I obtained a list of available COM ports and then simply iterated over them, if it didn't throw an exception i tried to communicate with the device. A bit rough but working.
var portNames = SerialPort.GetPortNames();
foreach(var port in portNames) {
//Try for every portName and break on the first working
}

This is how I did it:
[DllImport("kernel32.dll", CharSet = CharSet.Auto, SetLastError = true)]
internal static extern SafeFileHandle CreateFile(string lpFileName, int dwDesiredAccess, int dwShareMode, IntPtr securityAttrs, int dwCreationDisposition, int dwFlagsAndAttributes, IntPtr hTemplateFile);
then later on
int dwFlagsAndAttributes = 0x40000000;
var portName = "COM5";
var isValid = SerialPort.GetPortNames().Any(x => string.Compare(x, portName, true) == 0);
if (!isValid)
throw new System.IO.IOException(string.Format("{0} port was not found", portName));
//Borrowed from Microsoft's Serial Port Open Method :)
SafeFileHandle hFile = CreateFile(#"\\.\" + portName, -1073741824, 0, IntPtr.Zero, 3, dwFlagsAndAttributes, IntPtr.Zero);
if (hFile.IsInvalid)
throw new System.IO.IOException(string.Format("{0} port is already open", portName));
hFile.Close();
using (var serialPort = new SerialPort(portName, 115200, Parity.None, 8, StopBits.One))
{
serialPort.Open();
}

For people that cannot use SerialPort.GetPortNames(); because they are not targeting .net framework (like in my case I am using .Net Core and NOT .Net Framework) here is what I ended up doing:
In command prompt if you type mode you get something like this:
mode is an executable located at C:\Windows\System32\mode.com. Just parse the results of that executable with a regex like this:
// Code that answers the question
var proc = new Process
{
StartInfo = new ProcessStartInfo
{
FileName = #"C:\Windows\System32\mode.com",
UseShellExecute = false,
RedirectStandardOutput = true,
CreateNoWindow = true
}
};
proc.Start();
proc.WaitForExit(4000); // wait up to 4 seconds. It usually takes less than a second
// get ports being used
var output = proc.StandardOutput.ReadToEnd();
Now if you want to parse the output this is how I do it:
List<string> comPortsBeingUsed = new List<string>();
Regex.Replace(output, #"(?xi) status [\s\w]+? (COM\d) \b ", regexCapture =>
{
comPortsBeingUsed.Add(regexCapture.Groups[1].Value);
return null;
});
foreach(var item in comPortsBeingUsed)
{
Console.WriteLine($"COM port {item} is in use");
}

I wanted to open the next available port and did it like this.
Please note, is it not for WPF but for Windows Forms.
I populated a combobox with the com ports available.
Then I try to open the first one. If it fails, I select the next available item from the combobox. If the selected index did not change in the end, there were no alternate com ports available and we show a message.
private void GetPortNames()
{
comboBoxComPort.Items.Clear();
foreach (string s in SerialPort.GetPortNames())
{
comboBoxComPort.Items.Add(s);
}
comboBoxComPort.SelectedIndex = 0;
}
private void OpenSerialPort()
{
try
{
serialPort1.PortName = comboBoxComPort.SelectedItem.ToString();
serialPort1.Open();
}
catch (Exception ex)
{
int SelectedIndex = comboBoxComPort.SelectedIndex;
if (comboBoxComPort.SelectedIndex >= comboBoxComPort.Items.Count - 1)
{
comboBoxComPort.SelectedIndex = 0;
}
else
{
comboBoxComPort.SelectedIndex++;
}
if (comboBoxComPort.SelectedIndex == SelectedIndex)
{
buttonOpenClose.Text = "Open Port";
MessageBox.Show("Error accessing port." + Environment.NewLine + ex.Message, "Port Error!!!", MessageBoxButtons.OK);
}
else
{
OpenSerialPort();
}
}
if (serialPort1.IsOpen)
{
StartAsyncSerialReading();
}
}

The SerialPort class has an Open method, which will throw a few exceptions.
The reference above contains detailed examples.
See also, the IsOpen property.
A simple test:
using System;
using System.IO.Ports;
using System.Collections.Generic;
using System.Text;
namespace SerPort1
{
class Program
{
static private SerialPort MyPort;
static void Main(string[] args)
{
MyPort = new SerialPort("COM1");
OpenMyPort();
Console.WriteLine("BaudRate {0}", MyPort.BaudRate);
OpenMyPort();
MyPort.Close();
Console.ReadLine();
}
private static void OpenMyPort()
{
try
{
MyPort.Open();
}
catch (Exception ex)
{
Console.WriteLine("Error opening my port: {0}", ex.Message);
}
}
}
}

Sharing what worked for me (a simple helper method):
private string portName { get; set; } = string.Empty;
/// <summary>
/// Returns SerialPort Port State (Open / Closed)
/// </summary>
/// <returns></returns>
internal bool HasOpenPort()
{
bool portState = false;
if (portName != string.Empty)
{
using (SerialPort serialPort = new SerialPort(portName))
{
foreach (var itm in SerialPort.GetPortNames())
{
if (itm.Contains(serialPort.PortName))
{
if (serialPort.IsOpen) { portState = true; }
else { portState = false; }
}
}
}
}
else { System.Windows.Forms.MessageBox.Show("Error: No Port Specified."); }
return portState;
}
Notes:
- For more advanced technique(s) I recommend using ManagementObjectSearcher Class.
More info Here.
- For Arduino devices I would leave the Port Open.
- Recommend using a Try Catch block if you need to catch exceptions.
- Check also: "TimeoutException"
- More information on how to get SerialPort (Open) Exceptions Here.

public void MobileMessages(string ComNo, string MobileMessage, string MobileNo)
{
if (SerialPort.IsOpen )
SerialPort.Close();
try
{
SerialPort.PortName = ComNo;
SerialPort.BaudRate = 9600;
SerialPort.Parity = Parity.None;
SerialPort.StopBits = StopBits.One;
SerialPort.DataBits = 8;
SerialPort.Handshake = Handshake.RequestToSend;
SerialPort.DtrEnable = true;
SerialPort.RtsEnable = true;
SerialPort.NewLine = Constants.vbCrLf;
string message;
message = MobileMessage;
SerialPort.Open();
if (SerialPort.IsOpen )
{
SerialPort.Write("AT" + Constants.vbCrLf);
SerialPort.Write("AT+CMGF=1" + Constants.vbCrLf);
SerialPort.Write("AT+CMGS=" + Strings.Chr(34) + MobileNo + Strings.Chr(34) + Constants.vbCrLf);
SerialPort.Write(message + Strings.Chr(26));
}
else
("Port not available");
SerialPort.Close();
System.Threading.Thread.Sleep(5000);
}
catch (Exception ex)
{
message.show("The port " + ComNo + " does not exist, change port no ");
}
}

I have been fighting with this problem for a few weeks now. Thanks to the suggestions on here and from the site, https://www.dreamincode.net/forums/topic/91090-c%23-serial-port-unauthorizedaccessexception/ .
I finally came up with a solution that seems to work.
The application I am working on allows a user to connect to a USB device and display data from it.
The Problem I was battling. Along side the application I am writing, I use another serial terminal application for doing my testing. Sometimes I forget to disconnect the COMport being used on the other application. If I do, and try to connect with the application I am writing, I would get an “UnAuthorizedAccessException” error. Along with this exception came some side effects, such as double lines of data being spit out and the application locking up on closing down.
My Solution
Thanks to the advice on here and the other site referenced, this was my solution.
private void checkAndFillPortNameList()
{
SerialPort _testingSerialPort;
AvailablePortNamesFound.Clear();
List<string> availablePortNames = new List<string>();//mySerial.GetAvailablePortNames();
foreach (string portName in SerialPortDataAccess.GetAvailablePortNames())
{
try
{
_testingSerialPort = new SerialPort(portName);
_testingSerialPort.Open();
if (_testingSerialPort.IsOpen)
{
availablePortNames.Add(portName);
_testingSerialPort.Close();
}
}
catch (Exception ex)
{
}
}
availablePortNames.Sort();
AvailablePortNamesFound = new ObservableCollection<string>(availablePortNames);
}
This routine connects to a combobox which holds the available Comports for selection. If a Comport is already, in use by another application, that port name will not appear in the combo box.

You can try folloing code to check whether a port already open or not. I'm assumming you dont know specificaly which port you want to check.
foreach (var portName in Serial.GetPortNames()
{
SerialPort port = new SerialPort(portName);
if (port.IsOpen){
/** do something **/
}
else {
/** do something **/
}
}