listbox中内容定时刷新时，不会有明显的抖动，且使刷新后的scrollbar保持在刷新前的位置

1、我的程式listbox每秒刷新一次,拖动scrollbar后,刷新后scrollbar会自动回到顶端,怎样才能在刷新后使scrollbar在原来的位置,而不回到listbox顶端?
２、怎样才能在刷新时，listbox不会有明显的抖动
附上源码:  
using  System;  
using  System.Collections.Generic;  
using  System.ComponentModel;  
using  System.Data;  
using  System.Drawing;  
using  System.Text;  
using  System.Windows.Forms;  
using  System.Diagnostics;  
using  System.Collections;  
using  System.Threading;  
 
namespace  ProcessTest  
{  
       public  partial  class  Form1  :  Form  
       {  
               private  ArrayList  alist;  
               private  Process[]  process;  
               private  Thread  thread;  
               private  delegate  void  clear_datasource();  
               private  delegate  void  get_datasource();  
               public  Form1()  
               {  
                       InitializeComponent();  
               }  
 
               private  void  show_process()  
               {  
                       process  =  Process.GetProcesses();  
                       string  process_name;  
                       this.Invoke(new  clear_datasource(clear_list));  
                       alist.Clear();  
                       foreach  (Process  t  in  process)  
                       {  
                               process_name  =  t.ProcessName;  
                               alist.Add(process_name);  
                       }  
                       this.Invoke(new  get_datasource(get_list));  
                       Thread.Sleep(1000);  
                       show_process();  
               }  
 
               private  void  get_list()  
               {  
                       listBox1.DataSource  =  alist;  
               }  
 
               private  void  clear_list()  
               {  
                       listBox1.DataSource  =  null;  
               }  
 
               private  void  Form1_Load(object  sender,  EventArgs  e)  
               {  
                       alist  =  new  ArrayList();  
                       thread  =  new  Thread(new  ThreadStart(show_process));  
                       thread.Start();  
               }  
 
               private  void  Form1_FormClosing(object  sender,  FormClosingEventArgs  e)  
               {  
                       thread.Abort();  
               }  
       }  
}