Random "InvalidOperationException" when changing date in CalendarView [UWP]

Question

The code

private void DateChanged(CalendarView sender, CalendarViewSelectedDatesChangedEventArgs args)
{
    var myDate = args.AddedDates.First();
    string parsedDate = myDate.ToString();
}

randomly causes this exception

System.InvalidOperationException: 'Sequence contains no elements'

How can I avoid it?

You should check that args.AddedDates contains some elements before tying to get the first one and converting it. — swatsonpicken, Aug 08 '17 at 16:26

score 0 · Answer 1 · answered Aug 08 '17 at 16:30

This is because you are calling .First() on something which doesn't contain anything/is empty. A better idea would be to call FirstOrDefault() which returns null instead of an exception if you call it on an empty collection.

var myDate = args.AddedDates.FirstOrDefault();
if(myDate != null)
    MyButton.Content = myDate.ToString();

score 0 · Answer 2 · edited Aug 08 '17 at 16:38

0

It means that args.AddedDates is NULL or empty. So to avoid this error, you'll need to check if it's not null or empty.

private void DateChanged(CalendarView sender, CalendarViewSelectedDatesChangedEventArgs args)
{
    if (args.AddedDates != null && args.AddedDates.Count > 0)
    {
        var myDate = args.AddedDates.First();
        string parsedDate = myDate.ToString();
    }
}

edited Aug 08 '17 at 16:38

Michael Coxon

4,806
1
21
49

answered Aug 08 '17 at 16:31

Stef Geysels

957
10
23

score 0 · Answer 3 · answered Aug 08 '17 at 16:32

There is a couple things you can do here...

First you can allow for an empty collection..

private void DateChanged(CalendarView sender, CalendarViewSelectedDatesChangedEventArgs args)
{
    var myDate = args.AddedDates.FirstOrDefault();
    if (myDate != null)
    {
        string parsedDate = myDate.ToString();
    }
}

Secondly you could check the collection beforehand...

private void DateChanged(CalendarView sender, CalendarViewSelectedDatesChangedEventArgs args)
{
    if(args.AddedDates != null || args.AddedDates.Any())
    {
        var myDate = args.AddedDates.First();
        string parsedDate = myDate.ToString();
    }
}

Some simple debugging would have told you that the issue is probably in the AddedDates property.

swatsonpicken · Accepted Answer · 2017-08-08T16:40:18.543

0

Similar to other answers, but args could also be null so I would use:

if (args?.AddedDates != null && args.AddedDates.Any())
{
    var myDate = args.AddedDates.First();
    string parsedDate = myDate.ToString();
}

EDIT:

As has been pointed out, the above only works in C# 6.0 or higher. An alternative that will work in all versions is:

if (args != null && args.AddedDates != null && args.AddedDates.Any())
{
    var myDate = args.AddedDates.First();
    string parsedDate = myDate.ToString();
}

edited Aug 08 '17 at 16:40

answered Aug 08 '17 at 16:34

swatsonpicken

631
1
4
18

1

I would add in a clause here to say that this (null conditions) will only work on c# 6+. – Michael Coxon Aug 08 '17 at 16:37
Fair point @Michael Coxon. Edited accordingly. – swatsonpicken Aug 08 '17 at 16:40

Random "InvalidOperationException" when changing date in CalendarView [UWP]

4 Answers4