c#完美截断字符串（中文+非中文）

public static string Truncation(this HtmlHelper htmlHelper, string str, int len){if (str == null || str.Length == 0 || len <= 0){return string.Empty;}int l = str.Length;#region 计算长度int clen = 0;while (clen < len && clen < l){//每遇到一个中文，则将目标长度减一。if ((int)str[clen] > 128) { len--; }clen++;}#endregionif (clen < l){return str.Substring(0, clen) + "...";}else{return str;}}