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

[jcrcarmo]

Hi everybody,

 

Here's 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 I'll 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... Let's 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 :)

Edited December 19, 2005 by jcrcarmo

[Cags]

Using the method marble_eater suggests you don't 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 isn't 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.