Validate a DateTime in C#

Question

I doubt I am the only one who has come up with this solution, but if you have a better one please post it here. I simply want to leave this question here so I and others can search it later.

I needed to tell whether a valid date had been entered into a text box and this is the code that I came up with. I fire this when focus leaves the text box.

try
{
    DateTime.Parse(startDateTextBox.Text);
}
catch
{
    startDateTextBox.Text = DateTime.Today.ToShortDateString();
}

Answer 1

DateTime.TryParse This I believe is faster and it means you dont have to use ugly try/catches :)

e.g

DateTime temp;
if(DateTime.TryParse(startDateTextBox.Text, out temp))
//yay
else
// :(

Answer 2

I would use the DateTime.TryParse() method: http://msdn.microsoft.com/en-us/library/system.datetime.tryparse.aspx

Answer 3

Don't use exceptions for flow control. Use DateTime.TryParse and DateTime.TryParseExact. Personally I prefer TryParseExact with a specific format, but I guess there are times when TryParse is better. Example use based on your original code:

DateTime value;
if (!DateTime.TryParse(startDateTextBox.Text, out value))
{
    startDateTextox.Text = DateTime.Today.ToShortDateString();
}

Reasons for preferring this approach:

• Clearer code (it says what it wants to do)
• Better performance than catching and swallowing exceptions
• This doesn't catch exceptions inappropriately - e.g. OutOfMemoryException, ThreadInterruptedException. (Your current code could be fixed to avoid this by just catching the relevant exception, but using TryParse would still be better.)

Answer 4

What about using TryParse?

Answer 5

A problem with using DateTime.TryParse is that it doesn't support the very common data-entry use case of dates entered without separators, e.g. 011508.

Here's an example of how to support this. (This is from a framework I'm building, so its signature is a little weird, but the core logic should be usable):

    private static readonly Regex ShortDate = new Regex(@"^\d{6}$");
    private static readonly Regex LongDate = new Regex(@"^\d{8}$");

    public object Parse(object value, out string message)
    {
        msg = null;
        string s = value.ToString().Trim();
        if (s.Trim() == "")
        {
            return null;
        }
        else
        {
            if (ShortDate.Match(s).Success)
            {
                s = s.Substring(0, 2) + "/" + s.Substring(2, 2) + "/" + s.Substring(4, 2);
            }
            if (LongDate.Match(s).Success)
            {
                s = s.Substring(0, 2) + "/" + s.Substring(2, 2) + "/" + s.Substring(4, 4);
            }
            DateTime d = DateTime.MinValue;
            if (DateTime.TryParse(s, out d))
            {
                return d;
            }
            else
            {
                message = String.Format("\"{0}\" is not a valid date.", s);
                return null;
            }
        }

    }