string resultFileName = MD5Encrypt(NavigateUrl).Replace("=",string.Empty) + ".txt";
string newFilename = string.Empty;
//StringBuilder rBuilder = new StringBuilder(resultFileName);
//foreach (char rInvalidChar in Path.GetInvalidFileNameChars())
//{
// rBuilder.Replace(rInvalidChar.ToString(), string.Empty);
//}
或者使用linq中的Aggregate
var invalidFileName = Path.GetInvalidFileNameChars();
newFilename = invalidFileName.Aggregate(resultFileName, (o, r) => (o.Replace(r.ToString(),string.Empty)));