一、拼接字串的形式 

DateTime dt=Convert.ToDateTime("20220101".Substring(0,4)+"-"+"20220101".Substring(4,2)+"-"+"20220101".Substring(6,2))

二、Convert.ToDateTime(string)

string格式有要求，必須是yyyy-MM-dd hh:mm:ss 

三、Convert.ToDateTime(string, IFormatProvider)

DateTime dt;

DateTimeFormatInfo dtFormat = new System.GlobalizationDateTimeFormatInfo();

dtFormat.ShortDatePattern 
 
= "yyyy/MM/dd";

dt = Convert.ToDateTime("2022/05/26", dtFormat);

四、DateTime.ParseExact()

string dateString = "20220526";

DateTime dt = DateTime.ParseExact(dateString, "yyyyMMdd", System.Globalization.CultureInfo.CurrentCulture);

//或者

DateTime dt = DateTime.ParseExact(dateString, "yyyyMMdd", System.Globalization.CultureInfo.InvariantCulture);

五、DateTime.TryParse(string,out datetime)

https://docs.microsoft.com/zh-cn/dotnet/api/system.datetime.tryparse?view=net-6.0

DateTime.ParseExact

string str = "20220110"; 


 IFormatProvider ifp = new CultureInfo("zh-CN", true); 

DateTime dt = DateTime.ParseExact(str, "yyyyMMdd", ifp); 

MessageBox.Show(dt.ToString(
 
"yyyy-MM-dd")); 

DateTime.TryParseExact

string str = "20220110";

 

DateTime dt; 


IFormatProvider ifp = new CultureInfo("zh-CN", true);


if (DateTime.TryParseExact(str, "yyyyMMdd", ifp, DateTimeStyles.None, out dt)) 

{
      MessageBox.Show(dt.ToString(("yyyy-MM-dd"));

}