DateTime.TryParse issue with dates of yyyy-dd-MM f

问题:

I have the following date in string format "2011-29-01 12:00 am" . Now I am trying to convert that to datetime format with the following code:

DateTime.TryParse(dateTime, out dt); 

But I am alwayws getting dt as {1/1/0001 12:00:00 AM} , Can you please tell me why ? and how can I convert that string to date.

EDIT: I just saw everybody mentioned to use format argument. I will mention now that I can't use the format parameter as I have some setting to select the custom dateformat what user wants, and based on that user is able to get the date in textbox in that format automatically via jQuery datepicker.

回答1:

This should work based on your example "2011-29-01 12:00 am"

DateTime dt;
DateTime.TryParseExact(dateTime, 
                       "yyyy-dd-MM hh:mm tt", 
                       CultureInfo.InvariantCulture, 
                       DateTimeStyles.None, 
                       out dt);

回答2:

You need to use the ParseExact method. This takes a string as its second argument that specifies the format the datetime is in, for example:

// Parse date and time with custom specifier.
dateString = "2011-29-01 12:00 am";
format = "yyyy-dd-MM h:mm tt";
try
{
   result = DateTime.ParseExact(dateString, format, provider);
   Console.WriteLine("{0} converts to {1}.", dateString, result.ToString());
}
catch (FormatException)
{
   Console.WriteLine("{0} is not in the correct format.", dateString);
}

If the user can specify a format in the UI, then you need to translate that to a string you can pass into this method. You can do that by either allowing the user to enter the format string directly - though this means that the conversion is more likely to fail as they will enter an invalid format string - or having a combo box that presents them with the possible choices and you set up the format strings for these choices.

If it's likely that the input will be incorrect (user input for example) it would be better to use TryParseExact rather than use exceptions to handle the error case:

// Parse date and time with custom specifier.
dateString = "2011-29-01 12:00 am";
format = "yyyy-dd-MM h:mm tt";
DateTime result;
if (DateTime.TryParseExact(dateString, format, provider, DateTimeStyles.None, out result))
{
   Console.WriteLine("{0} converts to {1}.", dateString, result.ToString());
}
else
{
   Console.WriteLine("{0} is not in the correct format.", dateString);
}

A better alternative might be to not present the user with a choice of date formats, but use the overload that takes an array of formats:

// A list of possible American date formats - swap M and d for European formats
string[] formats= {"M/d/yyyy h:mm:ss tt", "M/d/yyyy h:mm tt", 
                   "MM/dd/yyyy hh:mm:ss", "M/d/yyyy h:mm:ss", 
                   "M/d/yyyy hh:mm tt", "M/d/yyyy hh tt", 
                   "M/d/yyyy h:mm", "M/d/yyyy h:mm", 
                   "MM/dd/yyyy hh:mm", "M/dd/yyyy hh:mm",
                   "MM/d/yyyy HH:mm:ss.ffffff" };
string dateString; // The string the date gets read into

try
{
    dateValue = DateTime.ParseExact(dateString, formats, 
                                    new CultureInfo("en-US"), 
                                    DateTimeStyles.None);
    Console.WriteLine("Converted '{0}' to {1}.", dateString, dateValue);
}
catch (FormatException)
{
    Console.WriteLine("Unable to convert '{0}' to a date.", dateString);
}                                               

If you read the possible formats out of a configuration file or database then you can add to these as you encounter all the different ways people want to enter dates.

回答3:

From DateTime on msdn:

Type: System.DateTime% When this method returns, contains the DateTime value equivalent to the date and time contained in s, if the conversion succeeded, or MinValue if the conversion failed. The conversion fails if the s parameter is null, is an empty string (""), or does not contain a valid string representation of a date and time. This parameter is passed uninitialized.

Use parseexact with the format string "yyyy-dd-MM hh:mm tt" instead.

回答4:

That works:

DateTime dt = DateTime.ParseExact("2011-29-01 12:00 am", "yyyy-dd-MM hh:mm tt", System.Globalization.CultureInfo.InvariantCulture);

回答5:

Try using safe TryParseExact method

DateTime temp;
string   date = "2011-29-01 12:00 am";

DateTime.TryParseExact(date, "yyyy-dd-MM hh:mm tt", CultureInfo.InvariantCulture, DateTimeStyles.None, out temp);

回答6:

DateTime dt = DateTime.ParseExact("11-22-2012 12:00 am", "MM-dd-yyyy hh:mm tt", System.Globalization.CultureInfo.InvariantCulture);

回答7:

If you give the user the opportunity to change the date/time format, then you'll have to create a corresponding format string to use for parsing. If you know the possible date formats (i.e. the user has to select from a list), then this is much easier because you can create those format strings at compile time.

If you let the user do free-format design of the date/time format, then you'll have to create the corresponding DateTime format strings at runtime.