serialport1在上下文中不存在

Question

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

namespace WindowsFormsApplication21
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void label1_Click(object sender, EventArgs e)
        {

        }

        private void button2_Click(object sender, EventArgs e)
        {
            button1.BackColor = Color.Red;
            label1.Text = " OCCUPIED";
        }

        private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
        {
          this.Invoke(new EventHandler(DoUpdate));
        }

        private void DoUpdate(object s, EventArgs e)
        {
            string InputString = serialPort1.ReadExisting();
            string[] data = InputString.Split(',');

            textBox1.Text = data[0];
            textBox2.Text = data[1];

           int b;
           int d;

           bool result = Int32.TryParse(data[0], out b);
           bool sonuc = Int32.TryParse(data[1], out d);
           if (result)
           {
               if (b < 224)
               {
                   button1.BackColor = Color.Red;
                   label1.Text = " OCCUPIED";
               }
               else
               {
                   button1.BackColor = Color.Lime;
                   label1.Text = "AVAILABLE";
               }
           }

           if (sonuc)
           {
               if (d< 224)
               {
                   button1.BackColor = Color.Red;
                   label1.Text = " OCCUPIED";
               }
               else
               {
                   button1.BackColor = Color.Lime;
                   label1.Text = "AVAILABLE";
               }
           }

        int b = Int16.Parse(a);
        textBox1.Text= a.ToString();*/

        private void button3_Click(object sender, EventArgs e)
        {
            listBox1.Visible = true;
            listBox1.Items.Add("Değerler alınıyor!");

            if (!serialPort1.IsOpen)
            {
                serialPort1.PortName = "COM11";
                serialPort1.Open();
            }
        }

        private void button4_Click(object sender, EventArgs e)
        {
            serialPort1.Close();
            listBox1.Items.Add("Durduruldu!");
        }
    }
} 

我收到了一个错误：

  

＆＃34; serialport1在上下文中不存在＆＃34;

我能做什么？每当我想编译时，我都会得到上面提到的错误 我是否需要添加任何库？
我正在使用visual Studio 2010