C# 将List＜string＞转换为List＜double＞

//string转List
List strList = new List();
strList.Add("100"); strList.Add("500"); strList.Add("700");
List douList = strList.ConvertAll(s => Convert.ToDouble(s));

string str = "600 650 700";
List douList2 = str.Split(' ').ToList().ConvertAll(s => Convert.ToDouble(s));

//List转string
string douStr = string.Join(" ", douList2.ConvertAll(s => Convert.ToString(s)));//douStr : 600 650 700