SerialReader

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.IO;
using System.IO.Ports;
using System.Threading;

namespace WindowsFormsApplication24
{
    public partial class Form1 : Form
    {
        SerialPort serialPort;
        private Action startReading;
        int bufferLength = 1024;
        string data;
        //Decoder utf8Decoder = Encoding.UTF8.GetDecoder();
        public Form1()
        {
            InitializeComponent();
            textBox1.ScrollBars = ScrollBars.Vertical;
            textBox1.WordWrap = false;
        }

        public bool Open()
        {
            serialPort = new SerialPort("COM4", 9600, Parity.None, 8, StopBits.One);
            bool result = false;
            try
            {
                
                this.serialPort.Open();
                result = true;
                startReading = StartAsyncSerialReading;
                startReading();
            }
            catch (Exception)
            {
                this.Close();
                result = false;
            }
            return result;

        }

        private void StartAsyncSerialReading()
        {
            byte[] buffer = new byte[bufferLength];
            serialPort.BaseStream.BeginRead(buffer, 0, bufferLength, delegate (IAsyncResult ar)
            {
                try
                {
                    if (serialPort.IsOpen)
                    {
                        int actualLength = serialPort.BaseStream.EndRead(ar);
                        byte[] received = new byte[actualLength];
                        Buffer.BlockCopy(buffer, 0, received, 0, actualLength);

                        

                        data += Encoding.ASCII.GetString(received, 0, actualLength);
                        while (data.Contains("\n"))
                        {
                            string message = data.Substring(0, data.IndexOf("\n"));
                            textBox1.Invoke(new Action(delegate ()
                            {
                                textBox1.AppendText(message+"\n");
                            }));
                            data = data.Substring(data.IndexOf("\n") + 1);
                        }

                    }
                }

                catch (IOException exc)
                {
                    //handleAppSerialError(exc);
                }

                if (serialPort.IsOpen)
                    startReading();

            }, null);

        }
        public void Dispose()
        {
            serialPort.Dispose();
            GC.SuppressFinalize(this);
        }


        public void ClosePort()
        {
            serialPort.BaseStream.Flush();
            serialPort.BaseStream.Close();
            this.serialPort.Close();
            this.Dispose();
            data = null;
            textBox1.AppendText("\n");

        }

        private void button2_Click(object sender, EventArgs e)
        {
            ClosePort();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            data = null;
            Open();
            StartAsyncSerialReading();
        }

        private void ClearButton_Click(object sender, EventArgs e)
        {
            textBox1.Text = String.Empty;
        }
    }
}