Question

I’m making a Gmail notifier with C# and Arduino.
The code checks whether it received mail and sends ‘m’ to serial if so.
It seems to work pretty well, but the problem is after I get this message once,

Unread mails: 0

this message keeps to print on the screen:

‘COM5’ port access denied.
‘COM5’ port access denied.
…

which obviously means that access to COM5 is denied after the code’s first trial.
I tried to add port.Close(); to my code, but then the code doesn’t loop after the second trial.
Kinda stuck here.
What seems to be the problem with my code?
Similar question seems to be on the web( Access to the port 'COM5' is denied ) but I don’t really understand how I could “wrap the use of SerialPort”.
Thank you!

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO.Ports;
using System.Threading;
using System.Net;
using System.Xml;

namespace GMailNotifier
{
    class GMail
    {
        public static void Main(string[] args)
        {
            while (true)
            {
                try
                {
                    SerialPort port = new SerialPort("COM5", 9600, Parity.None, 8, StopBits.One);
                    port.Open();

                    string Unreadz = "0";
                    Unreadz = CheckMail();
                    Console.WriteLine("Unread Mails: " + Unreadz);

                    if (!Unreadz.Equals("0")) port.Write("m");
                    else port.Write("n");
                }catch (Exception ee){ Console.WriteLine(ee.Message);
                }finally { System.Threading.Thread.Sleep(1000); }
            }
        }
    private static string CheckMail() {
        string result = "0";

        try {
        var url = @"https://gmail.google.com/gmail/feed/atom";
        var USER = "USER";
        var PASS = "PASS";

        var encoded = TextToBase64( USER + ":" + PASS );

        var myWebRequest = HttpWebRequest.Create( url ); 
        myWebRequest.Method = "POST";
        myWebRequest.ContentLength = 0;
        myWebRequest.Headers.Add( "Authorization", "Basic " + encoded );

        var response = myWebRequest.GetResponse();
        var stream = response.GetResponseStream();

        XmlReader reader = XmlReader.Create( stream );
        while ( reader.Read() )
            if ( reader.NodeType == XmlNodeType.Element )
            if ( reader.Name == "fullcount" ) {
                result = reader.ReadElementContentAsString();
                return result;
            }
        } catch ( Exception ee ) { Console.WriteLine( ee.Message ); }
        return result;
    }
    public static string TextToBase64(string sAscii){
        System.Text.ASCIIEncoding encoding = new System.Text.ASCIIEncoding();
        byte[] bytes = encoding.GetBytes(sAscii);
        return System.Convert.ToBase64String(bytes, 0, bytes.Length);
    }
  }
}

Answer 1

I don’t really understand how I could “wrap the use of SerialPort”.

It means to do something like this:

using (SerialPort port = new SerialPort("COM5", 9600, Parity.None, 8, StopBits.One))
{
    port.Open();

    string Unreadz = "0";
    Unreadz = CheckMail();
    Console.WriteLine("Unread Mails: " + Unreadz);

    if (!Unreadz.Equals("0")) port.Write("m");
    else port.Write("n");
}

The using statement will ensure that the SerialPort.Dispose method is called, to release the port after you have finished using it. If you don’t release it after the first time, then the hardware is still busy and you won’t be able to open it again (until it’s garbage-collected later).