reading rdata from serial port using C# in visual basic

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Threading;

namespace WindowsApplication1

{
    
   
    
    public partial class Form1 : Form
    {
        
    
       
        private delegate void SetTextDeleg(string text);
        string data = string.Empty;
        public Form1()
        {
            InitializeComponent();

           
            string[] ports = System.IO.Ports.SerialPort.GetPortNames();
            for (int i = 0; i < ports.Length; i++)
            {
                comboBox1.Items.Add(ports[i]);
            }
        }
private void button1_Click(object sender, EventArgs e)
        {
            try
            {
                
                serialPort1.PortName = "COM1";
                serialPort1.BaudRate = 9600;
                serialPort1.DataBits = 8;
                serialPort1.Parity = Parity.None;
                serialPort1.StopBits = StopBits.One;
                serialPort1.Open();
                serialPort1.ReadTimeout = 2000;
                serialPort1.DataReceived += new System.IO.Ports.SerialDataReceivedEventHandler(serialPort1_DataReceived);
                MessageBox.Show("Success to Connect");
                serialPort1.Close();
               
               
            }
            catch (Exception ex)
            {
                MessageBox.Show("Failed because" + ex.Message);

            }
        }



          private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
        {

              
            Thread.Sleep(500);
            data = serialPort1.ReadLine();
           
            this.BeginInvoke(new SetTextDeleg(si_DataReceived), new object[] { data }); 
            
             
        }

       
        private void si_DataReceived(string data)
        {
            listBox1.Items.Add(data);
        }