一些简单有用的方法合集

        /// <summary>
        /// 处理过长的显示字符串，只显示前几个字符，后面加上“...”
        /// 
        /// </summary>
        /// <param name="str">要处理的字符串</param>
        /// <param name="size">需要的长度</param>
        /// <returns></returns>
        public static string GetSeveralChar(string str, int size)
        {
            return Encoding.Default.GetBytes(str).Length > size ? Encoding.Default.GetString(Encoding.Default.GetBytes(str).Take(size).ToArray()).Replace("?", String.Empty) + "..." : str;
        }

        /// <summary>
        /// 注册JS
        /// 
        /// </summary>
        /// <param name="page"></param>
        /// <param name="Method"></param>
        public static void RegisterStartupScript(System.Web.UI.Page page, string Method)
        {
            page.ClientScript.RegisterStartupScript(page.GetType(), DateTime.Now.ToString(), "<script type='text/javascript'>" + Method + "</script>");
        }

        /// <summary>
        /// 根据数字得到二进制的字符串
        /// 
        /// </summary>
        /// <param name="num"></param>
        /// <returns></returns>
        public static string GetBlobFromNum(int num)
        {
            int len = sizeof(int) * 8;
            StringBuilder str = new StringBuilder();
            int exmple = 1 << len - 1;
            int tmp = num;
            for (int i = 0; i < len; i++)
            {
                str.Append((tmp & exmple) == 0 ? "0" : "1");
                tmp <<= 1;
            }
            return str.ToString().Substring(str.ToString().Length - 4);
        }
        /// <summary>
        /// 根据二进制获取数字集合
        /// 
        /// </summary>
        /// <param name="blob"></param>
        /// <returns></returns>
        public static string GetNumArrayByBlob(string blob)
        {
            string NumArray = string.Empty;
            for (int i = 0; i < blob.Length; i++)
            {
                if (blob.Substring(i, 1) == "1")
                {
                    NumArray = string.IsNullOrEmpty(NumArray) ? Get2ndPowerNum(blob.Length - i - 1).ToString() : NumArray + "," + Get2ndPowerNum(blob.Length - i - 1).ToString();
                }
            }
            return NumArray;
        }
        /// <summary>
        /// 计算2的N次方的方法
        /// 
        /// </summary>
        /// <param name="lenth"></param>
        /// <returns></returns>
        public static int Get2ndPowerNum(int lenth)
        {
            return lenth == 0 ? 1 : 2 * Get2ndPowerNum(lenth - 1);
        }
        /// <summary>
        /// 将List转换为字符串
        /// </summary>
        /// <param name="coll"></param>
        /// <returns></returns>
        public static string GetListCollectionByStr(List<string> coll)
        {
            string result = string.Empty;
            for (int i = 0; i < coll.Count; i++)
            {
                result = string.IsNullOrEmpty(result) ? coll[i] : result + "," + coll[i];
            }
            return result;

        }
       /// <summary>
        /// 从数组中随机取出多个不重复的项 
        /// 作者：刘仁和
        /// </summary>
        /// <param name="list"></param>
        /// <param name="num"></param>
        /// <returns></returns>
        public static IList<string> getListItems(IList<string> list, int num)
        {
            //新建一个泛型列表,将传入的列表复制过来,用于运算,而不要直接操作传入的列表;    

            //这样写是引用复制,不对啦
            //IList<string> temp_list = list;

            //另外这样写也要注意,也不是深度复制
            IList<string> temp_list = new List<string>(list);

            //取出的项,保存在此列表
            IList<string> return_list = new List<string>();

            //Random random = new Random(unchecked((int)DateTime.Now.Ticks));
            Random random = new Random();

            for (int i = 0; i < num; i++)
            {
                //判断如果列表还有可以取出的项,以防下标越界
                if (temp_list.Count > 0)
                {
                    //在列表中产生一个随机索引
                    int arrIndex = random.Next(0, temp_list.Count);
                    //将此随机索引的对应的列表元素值复制出来
                    return_list.Add(temp_list[arrIndex]);
                    //然后删掉此索引的列表项
                    temp_list.RemoveAt(arrIndex);
                }
                else
                {
                    //列表项取完后,退出循环,比如列表本来只有10项,但要求取出20项.
                    break;
                }
            }
            return return_list;
        }