CultureInfo & DateTimeInfo: How to check if is 24 hour time?

Question

I'm modifying a globalized web application which uses stored CultureInfo for each logged in user.

The client would like time data entry to be localized. Displaying is not a problem as the formatting is already available. However I need to detect if the current cultureinfo is for 24 hour time or am/pm so I can display the correct input boxes (not just a textfield).

My initial idea was to check the DateTimeInfo property of CultureInfo and see if the ShortTimePattern contained a capital H or a lower case h but this didn't feel robust enough for me.

Is there a better way? I've read the class properties of both but unless I'm missing something, I can't see any existing methods or properties.

Answer 1

I don't think there is a better way to obtain that information. The time pattern for a culture could contain anything (a user could even create a custom culture where the ShortTimePattern is "\hello" and then DateTime.ToString() would return "hello" for any time). In that case how could the framework determine if that CultureInfo is in 24-hour or 12-hour format?

So a "normal" DateTimeFormatInfo.ShortTimePattern will necessarily contain either a 'h' or a 'H', otherwise the hour will not be displayed. I think you can follow your initial idea and check for that. You can also check that the 'h' or 'H' is not escaped with a \ like in my "\hello" example because that would not represent the hour :)

Answer 2

The most robust way is to check if DateTimeFormatInfo.AMDesignator is an empty string.

if (DateTimeFormatInfo.CurrentInfo.AMDesignator == "")
  //24hour format
else
  //12hour format

Answer 3

Checking for 'H'/'h' seems more robust than checking for the AM/PM Designator. A good example is en-gb: The time format string is HH:mm and the AM/PM designators are set to AM/PM Windows will display the time in 24h format! This seems to be an inconsistent definition but checking for 'H' fixed my bug.