Parsing dates from a webpage

Question

I have two inputs (TextBox) on my front end.

The following code parses them from their string representation to aDateTime object. If it fails, it then sets default values.

DateTime dateFrom;
DateTime dateTo;
if (!DateTime.TryParse(txtDateFrom.Text, out dateFrom)) { dateFrom = DateTime.Today.AddDays(-7); }
if (!DateTime.TryParse(txtDateTo.Text, out dateTo)) { dateTo = DateTime.Now; }

However, the code looks bulky. Is there a better way to write it?

Answer 1

If you're doing this a lot, you could consider a custom method for it:

public static DateTime TryParse(object from, Func<DateTime> failureResult)
{
 DateTime result;
 if (!DateTime.TryParse(from, out result))
 {
 result = failureResult();
 }
 return result;
}

Or (for when you're not accessing time-sensitive DateTime values (i.e. not DateTime.Now()):

public static DateTime TryParse(object from, DateTime failureResult)
{
 DateTime result;
 if (!DateTime.TryParse(from, out result))
 {
 result = failureResult;
 }
 return result;
}

This calls the failureResult delegate that will return your DateTime if DateTime's TryParse fails.

Your usage would be:

DateTime dateFrom = TryParse(txtDateFrom.Text, ()=>DateTime.Today.AddDays(-7));
DateTime dateTo = TryParse(txtDateTo.Text, ()=> DateTime.Now);

Or with the second snippet:

DateTime dateFrom = TryParse(txtDateFrom.Text, DateTime.Today.AddDays(-7));
DateTime dateTo = TryParse(txtDateTo.Text, DateTime.Now);

Sadly you cannot make a static extension method so this will have to exist somewhere else (although you could make it an extension of string).

Answer 2

You won't be able to change the bulkiness much but there are a few things you can do:

• indent your code. It will take more space but it will also be more readable:

DateTime dateFrom;
DateTime dateTo;
if (!DateTime.TryParse(txtDateFrom.Text, out dateFrom)) 
{ 
 dateFrom = DateTime.Today.AddDays(-7); 
}
if (!DateTime.TryParse(txtDateTo.Text, out dateTo)) 
{ 
 dateTo = DateTime.Now; 
}

• Wait for C# 6 which has inline-out-variables. This will make it possible to write the TryParse like this:

if (!DateTime.TryParse(txtDateFrom.Text, out DateTime dateFrom))

or even

if (!DateTime.TryParse(txtDateFrom.Text, out var dateFrom))

• Use DateTime.UtcNow. By using DateTime.Now you're dependent on the location of your server which might be a problem some time in the future when you host it elsewhere.

• Consider making a datetime picker available in the frontend instead of a textbox. It's a lot more user-friendly and it will avoid invalid dates.

Answer 3

I like Nick Udell's concept, but I prefer using extension methods in this case and avoiding using negative cases - I find these more confusing at 2 AM, when something is broken, than using the positive case.

public static DateTime TryParse(this DateTime defaultValue, string TextToParse) 
{
 DateTime.TryParse(TextToParse, out defaultValue);
 return defaultValue;
}

Usage:

DateTime dateFrom = DateTime.Today.AddDays(-7).TryParse(txtDateFrom.Text); 
DateTime dateTo = DateTime.Now.TryParse(txtDateTo.Text);

• Nick Udell: Could simply be preference but DateTime.Today.AddDays(-7).TryParse(txtDateFrom.Text); would make me think I'm trying to get last week to do the parsing of the text, for some reason.
• AWinkle: @NickUdell, I see what you mean. I would probably switch the method name to something like "TryReplaceWith" to give better clarity.