windows 界面与代码分离的问题

  [DllImport("User32.dll", EntryPoint = "SendMessage")]        private static extern int SendMessage(               IntPtr hWnd,　　　// handle to destination window                int Msg,　　　 // message                IntPtr wParam,　// first message parameter                string lParam // second message parameter 
                 ); 
        public enum WindowsMessage
        {
            WM_USER = 0x0400
        }
        const int WM_USER = 0x0400;
        int testBytes = 0;
        string str = "111";
        public Form1()
        {
            InitializeComponent();
           
        }
       
        private delegate void TestDelegate();        private void StartMethod()
        {
            this.BeginInvoke(new TestDelegate(FasongXinxi));
        }
        private void button1_Click(object sender, EventArgs e)
        {
            StartMethod();          
        }        private void FasongXinxi()
        {
            for (int j = 0; j < 30; j++)
            {
            
                testBytes = Encoding.Default.GetByteCount(str);
                SendMessage(this.Handle, Convert.ToInt32(WindowsMessage.WM_USER), IntPtr.Zero, str);
                Thread.Sleep(2000);
                this.progressBar1.Value = j;
            }        }        public void print(string content)
        {
            if ((content != null) || (content != ""))
            {
                this.listBox1.Items.Add(DateTime.Now.ToString() + "  " + content);
                this.listBox1.Refresh();
            }
        }
        protected override void WndProc(ref Message m)
        {
            
            if (m.Msg == Convert.ToInt32(WindowsMessage.WM_USER))
            {                byte[] myBytes = new byte[testBytes];
                Marshal.Copy(m.LParam, myBytes, 0, testBytes);
                string myTestResult = Encoding.Default.GetString(myBytes);
                print(myTestResult);
            }
          
            base.WndProc(ref m);
        }     
    }我想实现界面 与代码分离,代码循环运行 当有需要界面显示的消息,界面listbox添加消息,没有消息时,界面能动,拉滚动条等,但现在这个,它每次都是循环完30次之后,界面才能动,我想程序运行一条2条3条..界面都能拖动,请大家帮忙,我是个初学者,希望帮忙的朋友解释详细点,谢谢