how to convert datetime? to datetime

Question

I have filed txtb_dateOfService is required to complete the form but if txtb_dateOfService is emapty return null if not TryParse the date > I had this error I don't know how to fix it

The best overloaded method match for 'System.DateTime.TryParse(string, out System.DateTime)' has some invalid arguments

    DateTime? dateOfService= null;
    if (string.IsNullOrEmpty(txtb_dateOfService.Text))
    {
        dateOfService = null;

    }
    else
        if (DateTime.TryParse(txtb_dateOfService.Text, out dateOfService))
        {

        }

Is there a reason you're using the nullable in the first place? This code looks like it could very easily be rewritten without nullables. — Joel Etherton, Jan 03 '13 at 17:59
You can also use the ?? operator in C# to "dereference" a nullable (and provide a default value if the nullable is in fact null). — ravuya, Jan 03 '13 at 18:01
What do you want to do if `txtb_dateOfService.Text` is not empty but not a valid (parseable) date/time value? — D Stanley, Jan 03 '13 at 18:10

score 6 · Accepted Answer · answered Jan 03 '13 at 17:59

6

You cannot pass a reference to DateTime? into a method expecting DateTime. You can solve this by introducing a temporary variable, like this:

else { // <<=== This is the final "else" from your code
    DateTime tmp;
    if (DateTime.TryParse(txtb_dateOfService.Text, out tmp))
    {
        dateOfService = tmp;
    } else {
        dateOfService = null;
    }
}

answered Jan 03 '13 at 17:59

Sergey Kalinichenko

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Shouldn't that be `dateOfService.Value = tmp`? – Joel Etherton Jan 03 '13 at 18:00
1

@JoelEtherton C# takes care of this automatically. – Sergey Kalinichenko Jan 03 '13 at 18:01
This will not work, check my answer. – Benjamin Toueg Jan 03 '13 at 18:19
@BenjaminToueg It looks like it did work for the OP, no? – Sergey Kalinichenko Jan 03 '13 at 18:21
It is actually not necessary to test for null or empty before. `TryParse` will handle these cases automatically by returning `false` and does not throw an exception. – Olivier Jacot-Descombes Jan 03 '13 at 18:32

Preston Guillot · Answer 2 · 2017-12-16T16:38:50.223

1

Your problem is converting DateTime? to DateTime, not vice versa. The DateTime.TryParse method's out parameter is not nullable; in the event TryParse fails the out parameter will be assigned DateTime.MinValue as its value. There is no reason to declare your dateOfService variable as a nullable type from this snippet.

edited Dec 16 '17 at 16:38

answered Jan 03 '13 at 18:00

Preston Guillot

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D Stanley · Answer 3 · 2013-01-03T18:09:46.780

You can either throw an exception if the parse fails:

DateTime? dateOfService= null;
if (string.IsNullOrEmpty(txtb_dateOfService.Text))
{
    dateOfService = null;
}
else
{
    // will throw an exception if the text is not parseable
    dateOfService = DateTime.Parse(txtb_dateOfService.Text);  
}

or use an intermediate DateTime to store the parsed result:

DateTime? dateOfService= null;
if (string.IsNullOrEmpty(txtb_dateOfService.Text))
{
    dateOfService = null;

}
else
{
    DateTime temp;
    if (DateTime.TryParse(txtb_dateOfService.Text, out temp))
    {
        dateOfService = temp;
    } 
    else 
    {
        dateOfService = null;
    }
}

Either of these can be logically simplified; I'm showing the full breakout to convey the logic.

score 0 · Answer 4 · answered Jan 03 '13 at 18:02

You can try to convert your string in a DateTime

DateTime? dataOfService = null;
DateTime output;

if (DateTime.TryParse(txtb_dateOfService.Text, out output))
   dataOfService = output;

now you can use dataOfService as a Nullable<DateTime> and check if it has a valid data converted using HasValue and Value properties.

score 0 · Answer 5 · answered Jan 03 '13 at 18:02

you need to create a temp value to hold the out parameter of TryParse:

DateTime tmp;
if (DateTime.TryParse(txtb_dateOfService.Text, out tmp)) {
    dateOfService = tmp;
} else{
    dateOfService = null;
}

A more terse example

DateTime tmp;
DateTime? dateOfService = DateTime.TryParse(txtb_dateOfService.Text, out tmp)
   ? tmp
   : (DateTime?)null;

score 0 · Answer 6 · answered Jan 03 '13 at 18:19

0

try out dateOfService.Value, this should work (I think)

answered Jan 03 '13 at 18:19

It'sNotALie.

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1

You can't pass properties as an out parameter, see: http://stackoverflow.com/questions/1370238/passing-a-property-as-an-out-parameter-in-c-sharp – Preston Guillot Jan 03 '13 at 18:25

how to convert datetime? to datetime

6 Answers6