serialport and dispatchertimer, how to make my thread pause when com port is open?

问题

i have a serial port that will iterate through the ports with this method:

foreach (string s in SerialPort.GetPortNames())
{
    var serialOneOfMany = new SerialPort(s, baudRate, Parity.None, 8, StopBits.One);
    if (serialOneOfMany.IsOpen)
    {
        serialOneOfMany.Close();
    }
    else
    {
        try
        {
            serialOneOfMany.Open();
        }
        catch
        {

            var openSerial = new System.Timers.Timer(3100);
            openSerial.Elapsed += (o, e) =>
            {
                serialOneOfMany.Open();
                openSerial.Enabled = false;

                openSerial.Dispose();
            };
            openSerial.Enabled = true;

        }                   
    }

    if (serialOneOfMany.IsOpen)
    {
        string received;

        try
        {
            lblPortNum.Content = s;
            lblPortNum.Refresh();


                serialOneOfMany.Write(testMessage);

            serialOneOfMany.DataReceived += new SerialDataReceivedEventHandler(testSerialPort_DataReceived);

        }
        catch (TimeoutException e)
        {
            serialOneOfMany.Close();
            continue;
        }
    }
} 

so, i want to open the port, send it a message, listen for the response, then close it. as everyone knows, every comport found in GetPortNames isn't a valid serial port. so, what i've been doing is setting a timer with a dispatcher timer:

DispatcherTimer time = new DispatcherTimer();
time.Interval = TimeSpan.FromMilliseconds(3000);
time.Tick += new EventHandler(someEventHandler);
time.Start();

here's the other method handled here:

private void someEventHandler(Object sender, EventArgs args)
{
    SerialPort serial = (SerialPort)sender;
    if (serial.IsOpen)
        serial.Close();
    serial.Dispose();

    //if you want this event handler executed for just once
    DispatcherTimer thisTimer = (DispatcherTimer)sender;
    thisTimer.Stop();
}

so, it'll open the com port, if it doesn't get a response within 3 seconds, it will close the port. the problem i'm having is that the foreach loop will just barrel through the code and open the comport several times, i'll get a message saying The COM Port is open already and can't be used. so basically it's not pausing in openSerial.

i want it to open a new serial port, and if it's not accessible, wait 3100 milliseconds and try again. how do i do that?

UPDATED CODE:

private void button1_Click(object sender, RoutedEventArgs e)
{
    CheckPorts();
}

private void checkPorts()
{
    SendMessage("messageToDevice1", 19200);
    SendMessage("Message2", 9600);
}



private void SendMessage(string testMessage, int baudRate)
{
    int baudRate = 9600;
    string testMessage = "test";
    txtPortName.Text = "Testing all serial ports";
    foreach (string s in SerialPort.GetPortNames())
    {
        SerialPort newPort = new SerialPort(s, baudRate, Parity.None, 8, StopBits.One);
        if (!newPort.IsOpen)
        {
            try
            {
                newPort.Open();
            }
            catch { }
        }
        if (newPort.IsOpen)
        {
            openPorts.Add(newPort);
            newPort.Write(testMessage);
            newPort.DataReceived += new SerialDataReceivedEventHandler(serialOneOfMany_DataReceived);
        }
        else
        {
            newPort.Dispose();
        }
    }
    txtPortName.Text = "Waiting for response";
    tmrPortTest.Enabled = true;
}

my new problem is that it just blows through the com ports, i need it to stop for each one, take a second to listen, then close it. it just blows through the foreach loop.

now, the reason why i don't just open up the port and keep it open through all the messages is that my devices have different baud rates, and i can't adjust them to all match. so, i need to open the ports, then send messages, listen, if they don't respond to the first round of messages, then open them up at the new baudrate and send a new batch of messages. but the foreachloop doens't pause for me to listen.

回答1:

I think this more or less agrees with rare's answer. The port where you receive a response (you would probably want to check the response as well) will remain open and all the others should close.

    private List<SerialPort> openPorts = new List<SerialPort>();

    private void button3_Click(object sender, EventArgs e)
    {
        int baudRate = 9600;
        string testMessage = "test";
        txtPortName.Text = "Testing all serial ports";
        foreach (string s in SerialPort.GetPortNames())
        {
            SerialPort newPort = new SerialPort(s, baudRate, Parity.None, 8, StopBits.One);
            if (!newPort.IsOpen)
            {
                try
                {
                    newPort.Open();
                }
                catch { }
            }
            if (newPort.IsOpen)
            {
                openPorts.Add(newPort);
                newPort.Write(testMessage);
                newPort.DataReceived += new SerialDataReceivedEventHandler(serialOneOfMany_DataReceived);
            }
            else
            {
                newPort.Dispose();
            }
        }
        txtPortName.Text = "Waiting for response";
        tmrPortTest.Enabled = true;
    }

    private void serialOneOfMany_DataReceived(object sender, SerialDataReceivedEventArgs e)
    {
        txtPortName.Text = ((SerialPort)sender).PortName;
    }

    private void tmrPortTest_Tick(object sender, EventArgs e)
    {
        tmrPortTest.Enabled = false;
        foreach (SerialPort port in openPorts)
        {
            if (port.PortName != txtPortName.Text)
            {
                port.Close();
                port.Dispose();
            }
        }
    }

回答2:

Here's how I would do this --

First, try to open all the serial ports. The ones that actually do open are put in a list.

Assign all serial ports in the list to the same DataReceived event handler. The event handler is where you will save the port name (it's in the args) and kill the timer if you rx'd the response

Send your testMessage out all the open ports

Set just one timer for 3.1 seconds

Close the ports once the timer fires or the event handler rx's the response.

来源：https://stackoverflow.com/questions/7911001/serialport-and-dispatchertimer-how-to-make-my-thread-pause-when-com-port-is-ope