C# 字符串20210128怎么转成2021-01-28

C# 字符串20210128怎么转成2021-01-28

方法一：在Insert()指定的位置插入" / "或者 " - "变成2021/01/28或者2021-01-28

string timeStr = "20210128";
timeStr = timeStr.Insert(4, "/");
timeStr = timeStr.Insert(7, "/");

方法二：用SubString()重新构造字符串

string timeStr = "20210128";
timeStr = timeStr.Substring(0, 4) + "-" + timeStr.Substring(4, 2) + "-" + timeStr.Substring(6, 2);

方法三：用DateTime.ParseExact(字符串，字符串格式，特定格式信息)

string timeStr = "20210128";
DateTime time = DateTime.ParseExact(timeStr, "yyyyMMdd", null);
timeStr = time.ToString("yyyy-MM-dd");