How to keep the values of the variables in a class

I'm creating a UWP application that will need to communicate with several modules (Arduino) over RS485.

At this time and for testing I created a small application that communicates with any of these modules without problems.

My problem is that my application will have more than one Page and to do these communications, I thought about creating a class to always keep the communications working.

The problem is that this way I can not keep the connection active, that is, after the communication starts, it loses its state.

Communications are initiated through this function:

private async Task initComm()
    {
        try
        {
            //cParam = PDB.getParameters();
            string selectedPortID = null;
            string aqs = SerialDevice.GetDeviceSelector();
            deviceInformation = await DeviceInformation.FindAllAsync(aqs);
            foreach (var devInfo in deviceInformation)
            {
                if (devInfo.Name == "USB-RS485 Cable")
                {
                    selectedPortID = devInfo.Id;
                }
            }

            serialPort = await SerialDevice.FromIdAsync(selectedPortID);


            if (serialPort != null)
            {
                serialPort.ReadTimeout = TimeSpan.FromMilliseconds(1000);
                serialPort.BaudRate = 9600; 
                serialPort.Parity = SerialParity.None; 
                serialPort.StopBits = SerialStopBitCount.One;
                serialPort.DataBits = 8;
            }
            else
            {
                var status = DeviceAccessInformation.CreateFromId(selectedPortID).CurrentStatus;
                // ELDB.attachEvent("E1002", "Starting Comunication Failed: " + status.ToString());
            }
            while (flagComm)
            {
                try
                {
                    await Listen();
                }
                catch (Exception ex)
                {
                    // ELDB.attachEvent("E2cC", ex.Message);
                }

            }
        }
        catch (Exception ex)
        {
            // ELDB.attachEvent("E1cC", ex.Message);
        }
    }

When I try to send something through this method:

private async void writeComm(string str2send)
    {
        try
        {
            using (var dataWriter = new DataWriter(serialPort.OutputStream))
            {
                dataWriter.WriteString(str2send);
                await dataWriter.StoreAsync();
                await dataWriter.FlushAsync();
                dataWriter.DetachStream();
            }
        }
        catch (Exception ex)
        {
            eventLog = ex.Message;
            // ELDB.attachEvent("E6cC", ex.Message);
        }
    }

What happens is that it goes into an exception because the referenced object no longer exists ...

Asyoucanseeintheimage,"serialPort == null"

What I would like to know is if it is possible to keep this idea of having a class with the methods and only calling them when I want to send something, or if I have to change the thinking.

If it's the second, is there any idea for this to work as intended?