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.

Xamarin Forms Bluetooth LE not showing nearby discoverable devices

I am making an app that utilizes bluetooth function such as scanning devices etc. I checked the scan flag and returns true but not showing the discoverable device that I am testing.
I am using Samsung J7 Pro as my app test device and Samsung J7 as the device I want to see in the list of discovered devices.
J7 already set as discoverable and with bluetooth ON.
I based my codes in Monkey.BluetoothLE
Here is what I have:
Declarations
ObservableCollection<BluetoothViewModel> vm = new ObservableCollection<BluetoothViewModel>();
Android.Bluetooth.BluetoothManager _blManager;
Android.Bluetooth.BluetoothManager _blManager;
Robotics.Mobile.Core.Bluetooth.LE.Adapter _bleAdapter;
Functions
public BluetoothPage()
{
InitializeComponent();
lvInfo.ItemsSource = vm;
var appContext = Android.App.Application.Context;
_blManager = (Android.Bluetooth.BluetoothManager)appContext.GetSystemService("bluetooth");
_blAdapter = _blManager.Adapter;
_bleAdapter = new Robotics.Mobile.Core.Bluetooth.LE.Adapter();
_bleAdapter.DeviceDiscovered += _bleAdapter_DeviceDiscovered;
_bleAdapter.ScanTimeoutElapsed += _bleAdapter_ScanTimeoutElapsed;
}
private void btnScanStopBluetooth_Click(object sender, EventArgs e)
{
if (!_bleAdapter.IsScanning)
{
if (!_blAdapter.IsEnabled)
{
_blAdapter.Enable();
DisplayInformation("Turning on bluetooth...");
while (!_blAdapter.IsEnabled)
{
//do nothing until enabled
}
}
vm.Clear();
btnScan.Text = "Stop Scan";
_bleAdapter.StartScanningForDevices();
}
else
{
btnScan.Text = "Start Scan";
_bleAdapter.StopScanningForDevices();
}
}
private void _bleAdapter_DeviceDiscovered(object sender, Robotics.Mobile.Core.Bluetooth.LE.DeviceDiscoveredEventArgs e)
{
count++;
vm.Add(new BluetoothViewModel
{
Name = e.Device.Name,
ID = e.Device.ID.ToString(),
RSSI = e.Device.Rssi.ToString()
});
}
private void _bleAdapter_ScanTimeoutElapsed(object sender, EventArgs e)
{
DisplayInformation("Scan Timeout");
_bleAdapter.StopScanningForDevices();
btnScan.Text = "Start Scan";
}
private void DisplayInformation(string line)
{
lblStatus.Text = line;
}
A listview is bound to "vm" that will display the discovered device.
It does not show anything, and count is always zero but I checked the scan flag using _bleAdapter.IsScanning, it returns true.
EDIT:
I tried other open-source sample programs for Bluetooth such as
xamarin-bluetooth-le (BLE Explorer)
Bluetooth-Xamarin.Forms (DemoBluetooth)
None of them seem to list the device. When I use my built-in bluetooth app under settings, it lists the device. What am I missing here?

Have you granted permission for bluetooth and location?
You have to grant permission in the Manifest/or Settings and depending on the sdk (23+) also asking the user for extra permission.
https://learn.microsoft.com/en-us/xamarin/android/app-fundamentals/permissions?tabs=windows

WinPcapDevice is still listening after stopping the capture

For some research of network activity on my private network, I came across NightHawk. So after downloading and testing, I tried to print out some Tcp packets when "sniffing". This worked for me very fine.
But when clicking the "stop button", the sniff function pauses for around 3 seconds and resumes sniffing to the network and printing arriving packets.
After searching for the missing -= of a "sniffing to the network" event handler, I found one and fixed it. BUT the problem is still active.
So for some reason - I can't find out - the OnPacketArrival event is still "alive" AND called from somewhere, even though I stopped capturing AND removed the event handler.
Edit:
As requested, here is some code:
// start listening on a device (combobox index)
public void StartDevice(int deviceIndex)
{
Started = true;
DeviceInfo = DeviceInfoList[deviceIndex];
Device = WinPcapDeviceList.Instance[deviceIndex];
Sniffer = new Sniffer(DeviceInfo);
ARPTools = new ARPTools(DeviceInfo);
NDTools = new NDTools(DeviceInfo);
SSLStrip = new SSLStrip();
Scanner = new Scanner(DeviceInfo);
Sniffer.SnifferResult += new SnifferResultHandler(sniffer_OnSnifferResult);
SSLStrip.SSLStripped += new SSLStripHandler(SSLStrip_OnSSLStripped);
Scanner.ScannerResponse += new ScannerResponseReceived(scanner_OnResponse);
Scanner.ScanComplete += new ScannerEventHandler(scanner_OnScanComplete);
Scanner.HostnameResolved += new ScannerHostnameResolvedHandler(scanner_HostnameResolved);
// open device, set filters & events, start capturing
Device.Open(DeviceMode.Promiscuous, 1);
Device.Filter = "(arp || ip || ip6)";
Device.OnPacketArrival += device_OnPacketArrival; // Subscribe the event for arriving packets
Device.StartCapture();
}
// stop listening on a device
public void StopDevice()
{
Started = false;
if (Device == null) return;
Device.StopCaptureTimeout = TimeSpan.FromMilliseconds(200);
Device.StopCapture();
Device.OnPacketArrival -= device_OnPacketArrival; // This is to unsubscribe the event. This was coded by me
Device.Close();
}
So has someone an explanation for this?
Thanks in advance!

Working with MIDI in Windows Store App (Win 8.1)

My goal is to receive MIDI messages in Windows Store Apps.
Microsoft has delivered an API called Microsoft.WindowsPreview.MidiRT (as a nuget package).
I managed to get a midi port, but MessageReceived event is not arised, although I'm pressing keys on my MIDI keyboard, and other MIDI programs show me that PC receives these messages.
Here is my code:
public sealed partial class MainPage : Page
{
private MidiInPort port;
public MainPage()
{
this.InitializeComponent();
DeviceWatcher watcher = DeviceInformation.CreateWatcher();
watcher.Updated += watcher_Updated;
watcher.Start();
}
protected override void OnNavigatingFrom(NavigatingCancelEventArgs e)
{
base.OnNavigatingFrom(e);
port.Dispose();
}
async void watcher_Updated(DeviceWatcher sender, DeviceInformationUpdate args)
{
DeviceInformationCollection deviceCollection = await DeviceInformation.FindAllAsync(MidiInPort.GetDeviceSelector());
foreach (var item in deviceCollection)
{
Debug.WriteLine(item.Name);
if (port == null)
{
port = await MidiInPort.FromIdAsync(item.Id);
port.MessageReceived += port_MessageReceived;
}
}
}
void port_MessageReceived(MidiInPort sender, MidiMessageReceivedEventArgs args)
{
Debug.WriteLine(args.Message.Type);
}
}
Any ideas?

Possibly-related: Your device watcher code is not following the normal pattern. Here is what you need to do:
DeviceWatcher midiWatcher;
void MonitorMidiChanges()
{
if (midiWatcher != null)
return;
var selector = MidiInPort.GetDeviceSelector();
midiWatcher = DeviceInformation.CreateWatcher(selector);
midiWatcher.Added += (s, a) => Debug.WriteLine("Midi Port named '{0}' with Id {1} was added", a.Name, a.Id);
midiWatcher.Updated += (s, a) => Debug.WriteLine("Midi Port with Id {1} was updated", a.Id);
midiWatcher.Removed += (s, a) => Debug.WriteLine("Midi Port with Id {1} was removed", a.Id);
midiWatcher.EnumerationCompleted += (s, a) => Debug.WriteLine("Initial enumeration complete; watching for changes...");
midiWatcher.Start();
}

I managed to make it work. I've changed the platfrom to x64, and now it works (I used to build it for x86). There is still a problem though (and it is even bigger): I want to integrate this with Unity3d, but Unity3d doesn't allow to build x64 windows apps, on the other hand x86 MIDI build doesn't work on x64 machines.
Added:
Although this API depends on your architecture, a new Windows 10 api reportedly does not, so it should be simpler, if you target Win10.

can not hit the SerialDataReceivedEvent?

All these comes from the idea that i want to use the SerialPort class in .Net , but the only way is by calling dll . Because i can only get interfaces from the program calling this dll. mycode is below.
i wrote a class about serialport,
public class CommClass
{
public SerialPort _port;
private string _receivedText;
public string receivedText
{
get { return _receivedText; }
set
{
_receivedText = value;
}
}
public CommClass(string _pname)
{
portList = SerialPort.GetPortNames();
_port = new SerialPort(portList[0]);
if (portList.Length < 1)
_port= null;
else
{
if(portList.Contains(_pname.ToUpper()))
{
_port = new SerialPort(_pname);
_port.DataReceived += new SerialDataReceivedEventHandler(com_DataReceived);
}
}
}
private void com_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
string indata = _port.ReadExisting();
receivedText = indata;
}
}
from Bytestoread i can see there r data coming in and i can get data from port.ReadExisting(), but receivedText did not change ,it did not hit the SerialDataReceived event . Is my way wrong?any suggestion?thanks
i created a dll from CommClass ,then i call it in my winform program which has a button and a textbox . Clicking the button , then i initialize the port
public Form1()
{
InitializeComponent();
}
public CommClass mycom;
private void button1_Click(object sender, EventArgs e)
{
mycom = new CommClass("com3");
mycom._port.Open();
textbox.Text=mycom.receivedText;//i add a breakpoint at this line ,
}
when hitting it , i check mycom._port.PortName is "com3", its IsOpen() is "Open" , i use virtual port to send data . i send "1111",then check the mycom._port.BytestoRead is 4, and mycom._port.ReadExisting() is "1111", but mycom.receivedText is null. My puzzle is that i have no idea when the data is coming . How to use the DataReceived event in my winform without code "using System.Io.Ports",just with reference CommClass.dll. Did i make it clear? Thanks for help.

mycom._port.Open();
textbox.Text=mycom.receivedText;//i add a breakpoint at this line ,
That code cannot work, it is a threading race bug. The DataReceived event does not fire instantly after you open the port. It will take a microsecond or so, give or take. A threadpool thread has to get started to fire the event. And of course the device actually has to send something, they usually only do so when you transmit something first.
Which clearly did not happen, your DataReceived event handler has a bug as well. It is not allowed to update the Text property of a control in that event since it runs on a worker thread. Your program will bomb with an InvalidOperationException.
You'll have to write something like this instead:
private void com_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
string indata = _port.ReadExisting();
this.BeginInvoke(new Action(() => {
textbox.AppendText(indata);
}));
}
With the additional stipulation that you must not leave it this way, updating the Text property of a TextBox and making it visible on the screen is an expensive operation that's going to turn your user interface catatonic when the device starts transmitting data at a high rate.