C#のシリアル通信練習

Form1.cs

using System.Windows.Forms;

namespace WindowsFormsApplication2
{
    public partial class Form1 : Form
    {
        string rxString;
        string comNum;

        public Form1()
        {
            InitializeComponent();

            foreach (var coms in System.IO.Ports.SerialPort.GetPortNames())
            {
                comBox.Items.Add(coms);
            }
        }

        private void startButton_Click(object sender, EventArgs e)
        {
            if (startButton.Text == "接続")
            {
                startButton.Text = "接続中";
                serialPort1.Open();

            }else if(startButton.Text == "接続中")
            {
                startButton.Text = "接続";
                serialPort1.Close();
            }
        }

        private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
        {
            rxString = serialPort1.ReadLine();
            this.Invoke(new EventHandler(DisplayText));
        }

        private void comBox_SelectedIndexChanged(object sender, EventArgs e)
        {
            
        }

        private void DisplayText(object sender, EventArgs e)
        {
            textBox1.AppendText(rxString + Environment.NewLine);
        }

        private void comBox_TextChanged(object sender, EventArgs e)
        {
            comNum = comBox.Text;
            serialPort1.PortName = comNum;
            serialPort1.BaudRate = 19200;
        }

        private void sendButton_Click(object sender, EventArgs e)
        {
            string message;
            message = textBox1.Text;
            serialPort1.WriteLine(message);
        }
    }
}

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace WindowsFormsApplication2
{
    static class Program
    {
        /// <summary>
        /// アプリケーションのメイン エントリ ポイントです。
        /// </summary>
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form1());
        }
    }
}