给string加几个扩展方法

    public static class StringExtend
    {
        public static bool IsNullOrEmpty(this string s)
        {
            return string.IsNullOrEmpty(s);
        }

        public static bool IsInt(this string s)
        {
            int i;
            return int.TryParse(s, out i);
        }

        public static int ToInt(this string s)
        {
            return int.Parse(s);
        }
    }