backgroundworker上运行异步方法,弹出等待窗口

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

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

        private ChildForm childForm = null;

        private void button1_Click(object sender, EventArgs e)
        {
            backgroundWorker1.WorkerReportsProgress = true;
            backgroundWorker1.WorkerSupportsCancellation = true;
            backgroundWorker1.DoWork += new DoWorkEventHandler(backgroundWorker1_DoWork);
            backgroundWorker1.ProgressChanged += new ProgressChangedEventHandler(backgroundWorker1_ProgressChanged);
            backgroundWorker1.RunWorkerCompleted += new RunWorkerCompletedEventHandler(backgroundWorker1_RunWorkerCompleted);
            childForm = new ChildForm();
            backgroundWorker1.RunWorkerAsync();
            childForm.ShowDialog(this);

        }

        private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            if (e.Error != null)
            {
                MessageBox.Show(e.Error.Message);
                return;
            }
            if (e.Cancelled)
            {
                childForm.label1.Text = "Cancelled!";
                Thread.Sleep(1200);
                backgroundWorker1.CancelAsync();
            }
            else
            {
                childForm.label1.Text = "Completed!";
            }
        }

        private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            childForm.progressBar1.Value = e.ProgressPercentage;//已将子窗体的progressbar设为public;
        }

        private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            Thread.Sleep(0); //等待子窗体建立完毕;
            for (int i = 0; i < 30; i++)
            {
                Thread.Sleep(200);
                backgroundWorker1.ReportProgress(i * 100 / 30);
                if (e.Cancel == true)
                {
                    backgroundWorker1.CancelAsync();
                }
            }
            backgroundWorker1.ReportProgress(100);

            serialPort1.WriteLine("\n");
            Thread.Sleep(2000);
            MessageBox.Show(serialPort1.ReadExisting());
            //这里老是为空.我的串口不用backgroundworker的话(调用一个普通方法)可以测试通过!
            //我在考虑是不是改为同步阻塞读取,因为ReadExisting()是异步读取.

        }
    }
}