how to write text box values to an excel sheet using c#?

namespace textboxtoexcel
{
    public partial class Form1 : Form
    {
        private bool stop = false;
        private Workbook workbook = null;
        private Worksheet worksheet = null;
        private int rowIndex = 0;
        private String fileName = null;
        public Form1()
        {
            InitializeComponent();
        }
        private void labelSize_TextChanged(object sender, EventArgs e)
        {
            if (stop)
            {
                return;
            }
            String no = String.Format("No. {0}", rowIndex);
            rowIndex++;
            worksheet[rowIndex, 1].Text = no;
            worksheet[rowIndex, 2].Text = this.labelSize.Text;
        }
        private void InitWorkbook()
        {
            workbook = new Workbook();
            workbook.CreateEmptySheets(1);
            worksheet = workbook.Worksheets[0];
            worksheet.Name = "image size";
            worksheet.Range[1, 1].Text = "No";
            worksheet.Range[1, 2].Text = "Size Data";
            rowIndex = 1;
            fileName = String.Format("image-size-{0}.xls", Guid.NewGuid());
        }
        private void btnDemoStart_Click(object sender, EventArgs e)
        {
            this.btnOpenExcel.Enabled = false;
            this.stop = false;
            this.InitWorkbook();
            Random random = new Random();
            new Thread(() =>
            {
                while(!this.stop)
                {
                    int width = random.Next(1024);
                    int height = random.Next(1024);
                    this.Invoke(new Action(() =>
                    {
                        this.labelSize.Text = String.Format("{0}, {1}", width, height);
                    }));
                    Thread.Sleep(1000);
                }
            }).Start();
        }
        private void btnDemoStop_Click(object sender, EventArgs e)
        {
            this.stop = true;
            this.btnOpenExcel.Enabled = true;
            this.workbook.SaveToFile(fileName);
        }
        private void btnOpenExcel_Click(object sender, EventArgs e)
        {
            System.Diagnostics.Process.Start(fileName);
        }
    }
}