http://blog.163.com/very_apple/blog/static/2775923620146304190249
List<string>转换成字符串
List<string> list = new List<string>();
list.Add("a");
list.Add("b");
list.Add("c");
string str = string.Join(",", list.ToArray());
字符串转成List<string>
string str = "a,b,c";
List<string> list = new List<string>(str.Split(','));
List<string> list = new List<string>(str.Split(new string[] { "," }, StringSplitOptions.RemoveEmptyEntries)); //转换时不包含空项