.net core 時間格式轉換

//string time = "2019-01-18 13:50:38";
string time = "2019-01-18 13:50:38 256";

//倆種格式都能識別
r= DateTime.ParseExact(time, new string[] { "yyyy-MM-dd HH:mm:ss fff", "yyyy-MM-dd HH:mm:ss" }, System.Globalization.CultureInfo.CurrentCulture);