How to Validate a DateTime in C#?

Question

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
{
  // Aww.. :(
}

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.)

Here's another variation of the solution that returns true if the string can be converted to a DateTime type, and false otherwise.

public static bool IsDateTime(string txtDate)
{
    DateTime tempDate;
    return DateTime.TryParse(txtDate, out tempDate);
}

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

What about using TryParse?

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;
            }
        }

    }