How to validate DateTime format?

user_1459321 0
Viewed 52974

I am suppose to let the user enter a DateTime format, but I need to validate it to check if it is acceptable. The user might enter "yyyy-MM-dd" and it would be fine, but they can also enter "MM/yyyyMM/ddd" or any other combination. Is there a way to validate this?

validation datetime c#
9 Answers

This works for me-

try
{
  String formattedDate = DateTime.Now.ToString(dateFormat);
  DateTime.Parse(formattedDate);
  return true;
}
catch (Exception)
{
  return false;
}
user_91805630 
static private bool IsValidDateFormat(string dateFormat)
{
  try
  {
    DateTime pastDate = DateTime.Now.Date.Subtract(new TimeSpan(10, 0, 0, 0, 0));
    string pastDateString = pastDate.ToString(dateFormat, CultureInfo.InvariantCulture);
    DateTime parsedDate = DateTime.ParseExact(pastDateString, dateFormat, CultureInfo.InvariantCulture);
    if (parsedDate.Date.CompareTo(pastDate.Date) ==0)
    {
      return true;
    }
    return false;
  }
  catch
  {
    return false;
  }
}

I do use this code - it is a modification of shapiro yaacov posting. It looks as "DateTime.ParseExact" does not throw an exception when using an invalid dateformat string - it just returns "DateTime.Now". My approach is to convert a date in the past to string and then check if this is returned by ParseExact()

user_25022010

The answer by ZipXap accepts any format that doesn't throw an exception, yet something like "aaaa" will pass that validation and give the current date at midnight ("26-Apr-22 00:00:00" when writing this).

A better aproach is to use the DateTimeStyles.NoCurrentDateDefault option and compare the result to default:

using System.Globalization;

var format = "aaaaa";
try {
    var dt = DateTime.ParseExact(
        DateTime.Now.ToString(format, CultureInfo.InvariantCulture),
        format,
        CultureInfo.InvariantCulture,
        DateTimeStyles.NoCurrentDateDefault);
    return dt != default;
} catch {
    return false;
}
/*
"aaaaa" -> false
"h" -> false
"hh" -> true
"fff" -> true
"gg" -> false
"yyyy gg" -> true
"'timezone: 'K" -> false
"zzz" -> false
*/
user_114278410
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