Dates in C# 2005 Express - Conversion, Validation and Comparison

[jcrcarmo]

Hi everybody,

Heres a few lines of code for a task that nearly drove me insane: convert, validate and compare dates from two different unbound MaskedTextBoxes. I hope it helps you guys out there... Special thanks to Cags and Marble Eater!

By for now,

JC


//------------------------------------------------------------------------------------------------------------------

class DateTimeUtils
{

public static bool IsDate(string strDate)
{
DateTime dtDate;
bool bValid = true;
try
{
dtDate = DateTime.Parse(strDate);
}
catch (FormatException)
{
MessageBox.Show("You have entered an invalid date. ", "Atention", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
bValid = false;
}
return bValid;
}

}


//------------------------------------------------------------------------------------------------------------------

private void DateIni_KeyUp(object sender, KeyEventArgs e)
{
if (this.DateIni.MaskCompleted)
{
string myDI = DateIni.Text;

if (DateTimeUtils.IsDate(myDI))
{
DateFin.Focus();
}
else
{
DateIni.Text = "";
DateIni.Focus();
}
}
}

//------------------------------------------------------------------------------------------------------------------

private void DateFin_KeyUp(object sender, KeyEventArgs e)
{
if (this.DateFin.MaskCompleted)
{
string myDI = DateIni.Text;
string myDF = DateFin.Text;

if (DateTimeUtils.IsDate(myDF))
{
DateTime DI = DateTime.Parse(myDI);
DateTime DF = DateTime.Parse(myDF);

if (DateTime.Compare(DI, DF) < 0)
{
EnableButtons();
}
else
{
MessageBox.Show("The final date value has to be bigger than the initial date value. ", "Atention", MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
DisableButtons();
DateFin.Text = "";
DateFin.Focus();
}
}
}
}


//------------------------------------------------------------------------------------------------------------------

 

[snarfblam]

I pointed this out in your other post as an edit, but Ill put it here too. Code like this is a bad thing...

		public bool IsDate(object inValue)
		{
			bool bValid;
 
			try 
			{
				DateTime myDT = DateTime.Parse(inValue);
				bValid = true;
			}
			catch (FormatException e) 
			{
				bValid = false;
			}
 
			return bValid;
		}

The reason is that it uses exception handling as a means of validation, which is not what exceptions are meant for. If exceptions can be avoided in a perfectly logical manner they should be. This means that we should not assume dates are formatted correctly, which the DateTime.Parse function does (unless we have a good reason to make such an assumption), but rather use a function that does not make such an assumption: DateTime.TryParse. This way, we can save the use of exceptions for what they are meant for: catastophic, exceptional, unexpected situations. If your code expects an exception, you did something wrong.

 

[jcrcarmo]

Hi MarbleEater,

I think understand what you mean, but the code I posted above is a tweaked version of your code and it was the only way I could make it work in my application. Everything else I tried failed... Lets suppose the user enters an incorrect date value by mistake, like for example 30/02/2005 (Feb 30). The TryParse method would make the app halt. How would you rewrite that code? Thanks in advance for your help.

Bye for now,

JC

 

[Cags]

Using the method marble_eater suggests you dont need an IsDate function at all you would just do the following...

bool bValid;
DateTime myDate;
string sDate;

bValid = DateTime.TryParse(sDate, out myDate);

if(bValid)
{
   MessageBox.Show("Valid");
   // any other code...
}
else
{
   MessageBox.Show("InValid");
   // any other code...
}

On a side note, I believe this is a 2.0 feature only as my VisualStudio does not support the TryParse() method and as far as I know there isnt a better way of doing it in 1.1 than the one I suggest. I realise the exception would be expensive but am un-aware of any way round the problem.

 

[snarfblam]

According to MSDN, TryParse is only available for the Double data type in versions 1.0 and 1.1 of the .Net framework. It is available for Int16/32/64, UInt8/16/32/64, byte, single (float), double, DateTime, etc. in version 2.0.