SerialDevice.FromIdAsync() yields a null serial port

问题

I have something strange happening with my code when trying to connect to a serial port. When using Serial Sample, everything works just fine and it connects on the first try. However, with my code the serial port returns a null.

I have found a workaround by nested the call to write the serial port in a do loop until the serial port is no longer null and it works. It takes, on average, 500 loops to connect and it has always connected. I know it's dangerous because there is the infinite loop if it's always null, so I tried switching the do loop to a for loop. With a for loop, it always returns back as null, even when I iterate it 50,000 times. Has anyone else encountered this and found a better solution? I'm connecting to an Arduino Uno.

The reason I'm not just using the Serial Sample code is because I want to use a drop down menu and use the port name instead of the device id name. My code is below. Thanks.

    //lists com ports
    private async void listPorts()
    {
        try
        {
            string aqs = SerialDevice.GetDeviceSelector();
            var dlist = await DeviceInformation.FindAllAsync(aqs);
            status.Text = "Select a device and connect";

            for (int i = 0; i < dlist.Count; i++)
            {
                var port = await SerialDevice.FromIdAsync(dlist[0].Id);
                ConnectDevices.Items.Add(port.PortName);
            }

            comConnect.IsEnabled = true;
            ConnectDevices.SelectedIndex = 0;
        }
        catch (Exception ex)
        {
            status.Text = ex.Message;
        }
    }

    //connects to the selected com port
    private async void comConnect_Click(object sender, RoutedEventArgs e)
    {
        _key = 0;
        status2.Text = "";
        string aqs = SerialDevice.GetDeviceSelector(ConnectDevices.SelectedItem.ToString());
        var dlist = await DeviceInformation.FindAllAsync(aqs);
        if (dlist.Count <= 0)
        {
            status.Text = "No devices found.";
            return;
        }
        try
        {
            do
            {
                serialPort = await SerialDevice.FromIdAsync(dlist[0].Id);
                status.Text = "Connecting to serial port...";
            } while (serialPort == null);

            // Configure serial settings
            serialPort.WriteTimeout = TimeSpan.FromMilliseconds(1000);
            serialPort.BaudRate = 38400;
            serialPort.Parity = SerialParity.None;
            serialPort.StopBits = SerialStopBitCount.One;
            serialPort.DataBits = 8;
            serialPort.Handshake = SerialHandshake.None;
            status.Text = "Serial port configured successfully.";

I have added the following to package.appmanifest

<Capabilities>
 <DeviceCapability Name="serialcommunication">
  <Device Id="any">
   <Function Type="name:serialPort" />
  </Device>
 </DeviceCapability>
</Capabilities>

回答1:

In my project, the serial port work correctly after I add the following code to package.appmanifest.

    <Capabilities>
     <DeviceCapability Name="serialcommunication">
      <Device Id="any">
       <Function Type="name:serialPort" />
      </Device>
     </DeviceCapability>
    </Capabilities>

The serial port variable should be "serialPort".

回答2:

This code working well with my com port and Arduino:

string aqs = SerialDevice.GetDeviceSelector("COM3");
DeviceInformationCollection dlist = await DeviceInformation.FindAllAsync(aqs);

if (dlist.Any())
{
 deviceId = dlist.First().Id;
}

using (SerialDevice serialPort = await SerialDevice.FromIdAsync(deviceId))
{
// .....
}

Try to specify com port

来源：https://stackoverflow.com/questions/37505107/serialdevice-fromidasync-yields-a-null-serial-port

标签

serial-port

uwp