Regular expression validator for Date(yyyy/MM/dd) or year(yyyy)

Question

I want regular validation expression to validate that only year (yyyy) or date is entered (yyyy-MM-dd).

It must not accept:

21,
23323

Answer 1

You don't need to use regex for that.

I would use DateTime.TryParseExact overload that takes string[] as a parameter.

string s = "2012";
DateTime dt;
var formats = new[] {"yyyy", "yyyy-MM-dd"};
if(DateTime.TryParseExact(s, formats, CultureInfo.InvariantCulture,
                          DateTimeStyles.None, out dt))
{
    // Your string is a valid DateTime for yyyy or yyyy-MM-dd format.
}

You said yyyy-MM-dd in your question but you said yyyy/MM/dd in your title. Add them to your formats array which one you try to validate.