using System.Text.RegularExpressions;
string numberStr = Regex.Match (str, "[0-9]").Value;
参考：
http://answers.unity3d.com/questions/19053/extract-number-from-string.html
ref: https://msdn.microsoft.com/en-us/library/system.text.regularexpressions.match(v=vs.110).aspx
c#, extract number from string
原文：http://www.cnblogs.com/wantnon/p/4598553.html