BackgroundWorker在单独的线程上执行操作

BackgroundWorker bw;
        //要计算的斐波那契数列的位数
        int numberToComputer = 0;
        //当前完成的比例，按时间来算是不准确的
        int hightest = 0;
        private void Form1_Load(object sender, EventArgs e)
        {
            bw = new BackgroundWorker();
            //是否要报告进度
            bw.WorkerReportsProgress = true;
            //是否允许取消
            bw.WorkerSupportsCancellation = true;
            //工作事件
            bw.DoWork += new DoWorkEventHandler(bw_DoWork);
            //进度变化事件
            bw.ProgressChanged += new ProgressChangedEventHandler(bw_ProgressChanged);
            //运行完成事件
            bw.RunWorkerCompleted += new RunWorkerCompletedEventHandler(bw_RunWorkerCompleted);
        }
        void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
        {
            //如果操作没有被取消，显示结果
            if (e.Cancelled)
            {
                label1.Text = "Cancelled";
            }
            else
            {
                label1.Text = e.Result.ToString();
            }
        }
        void bw_DoWork(object sender, DoWorkEventArgs e)
        {
            //此处要注意不要跨线程操作
            //如果后台操作需要参数，请在调用 RunWorkerAsync 时给出参数。
            //在 DoWork 事件处理程序内部，可以从 
            //oWorkEventArgs.Argument 属性中提取该参数。
            e.Result = Fib((int)e.Argument, bw, e);
        }
        void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
        {
            //显示当前进度
            this.progressBar1.Value = e.ProgressPercentage;
            lblPrecent.Text = e.ProgressPercentage.ToString();
        }
        /// <summary>
        /// 使用递归计算斐波那契数列的指定位数的值
        /// 1,1,2,3,5,8,13
        /// </summary>
        /// <param name="n">要计算的数</param>
        /// <param name="bwr">运行的后台进程</param>
        /// <param name="e">参数</param>
        /// <returns>运算结果</returns>
        long Fib(int n, BackgroundWorker bwr, DoWorkEventArgs e)
        {
            long result = 0;
            //如果已被取消，设置参数值取消为真
            if (bwr.CancellationPending)
            {
                e.Cancel = true;
            }
            else
            {
                if (n < 2)
                {
                    result = 1;
                }
                else
                {
                    result = Fib(n - 1, bwr, e) + Fib(n - 2, bwr, e);
                }
                //计算进度
                int p = (int)((float)n * 100 / (float)numberToComputer);
                //进度比上次有变化
                if (p > hightest)
                {
                    //最高进度为当前进度
                    hightest = p;
                    //报告进度
                    bw.ReportProgress(p);
                }
            }
            return result;
        }
        private void btnStart_Click(object sender, EventArgs e)
        {
            //如果不忙
            if (!bw.IsBusy)
            {
                //初始进度条
                progressBar1.Value = 0;
                //开始时最高进度为0
                hightest = 0;
                //要进行耗时计算的数字
                numberToComputer = Convert.ToInt32(numericUpDown1.Value);
                //异步运行
                bw.RunWorkerAsync(numberToComputer);
            }
            else
            {
                MessageBox.Show("busy");
            }
        }
        private void btnCancel_Click(object sender, EventArgs e)
        {
            //取消正在进行的操作
            bw.CancelAsync();
        }