结合网上的资料，自己记录一下

//1.把字符串转换成数组

string ls_str="122,158,141,236,896,123,122,158,141";

string[] str_num=ls_str.Split(',');

  //2.定义ArrayList,判断数组中重复字段不添加到 ArrayList对象中

   ArrayList al = new ArrayList();
   for (int i = 0; i < str_num.Length; i++)
    {

　　//判断是否已经存在
     if (al.Contains(str_num[i]) == false)
        {
           al.Add(str_num[i]);
         }

    }

  //3.将arrayList转换成数组
   str_num= new String[al.Count];
   str_num= (string[])al.ToArray(typeof(string));