为什么 DateTime.TryParseExact 不起作用？

Question

I am reading date from Excel and stored it in a variable In_Date , formats with which the date is to be compared is stored in Valid_Date_Formats

In_Date = "08/01/2020 00:00:00"

Valid_Date_Formats is an array which stores multiple date formats.

I am checking the format in if condition but it always fails.

If(DateTime.TryParseExact(In_Date, Valid_Date_Formats,
    System.Globalization.CultureInfo.InvariantCulture,
    System.Globalization.DateTimeStyles.None,
    DateTime_PlaceHolder))

What am I doing wrong here.

Answer 1

The input string has the following format: dd/MM/yyyy HH:mm:ss , which is missing from Valid_Date_Formats . (I'm assuming the 08 here is the day, because all your other formats start with the date part.)

The following returns the correct date:

DateTime.ParseExact("08/01/2020 00:00:00", new[] { "dd/MM/yyyy HH:mm:ss" }, CultureInfo.InvariantCulture, DateTimeStyles.None)

In response to your comment: I'm not aware of a built-in method that would tell you which exact format string was used. If you really need to find out, I guess you could traverse the formats until you find a match:

string[] formats = new[] { "dd/MM/yyyy", "dd/MM/yyyy HH:mm:ss" };
string input = "08/01/2020 00:00:00";

string usedFormat = null;
DateTime date;

foreach (string format in formats)
{
    if (DateTime.TryParseExact(input, format, CultureInfo.InvariantCulture, DateTimeStyles.None, out date))
    {
        usedFormat = format;
        break;
    }
}