progressBar如何不阻塞ui線程

                       MethodInvoker mi = new MethodInvoker(() =>
                        {
                            progressBar1.Value += progressBar1.Step;
                            this.lblprass.Text = this.progressBar1.Value.ToString() + "/" + this.progressBar1.Maximum.ToString();
                        });
                        this.BeginInvoke(mi);
                        System.Threading.Thread.Sleep(1000);//暫停1秒