What's wrong with the following method call?

Question

Possible Duplicate:
What is a NullReferenceException in .NET?

I have a Model (ASP.NET MVC 4, C#) Called HoursOfOperation:

public class HoursOfOperation
{
    public List<DayTimes> Monday { get; set; }
    public List<DayTimes> Tuesday { get; set; }
    public List<DayTimes> Wednesday { get; set; }
    public List<DayTimes> Thursday { get; set; }
    public List<DayTimes> Friday { get; set; }
    public List<DayTimes> Saturday { get; set; }
    public List<DayTimes> Sunday { get; set; }
}

and a DayTimes

public class DayTimes
{
    public int Status { get; set; }
    public string From { get; set; }
    public string To { get; set; }
}

now I'm trying to add a new set to the Monday entity like below:

var _vm = new HoursOfOperation();

_vm.Monday.Add(new DayTimes{
      From = day.From.ToString(),
      To = day.To.ToString(),
      Status = (int)day.Status
});

as soon as the above statement is excecuted I'm getting a "Object reference not set to an instance of an object." Exception

Now I have checked and day.From.ToString() has a "08:00:00", day.To.ToString() has "09:30:00" and day.Status has a 1 at the time at which this statement throws the exception.

Any Ideas?

Almost all cases of NullReferenceException are the same. Please see "[What is a NullReferenceException in .NET?](http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-in-net)" for some hints. — John Saunders, Jan 18 '13 at 03:07

score 5 · Accepted Answer · answered Jan 18 '13 at 03:08

5

That's because Monday is not instantiated.

You should do something like

_vm.Monday = new List<DayTimes>();

or alternatively, make all instantiations in HoursOfOperation's constructor like so:

public HoursOfOperation()
{
   Monday = new List<DayTimes>(),
   Tuesday = new List<DayTimes>(),
   Wednesday = new List<DayTimes>(),
   Thursday = new List<DayTimes>(),
   Friday = new List<DayTimes>(),
   Saturday = new List<DayTimes>(),
   Sunday = new List<DayTimes>()
};

answered Jan 18 '13 at 03:08

Ofer Zelig

15,893
7
52
89

Wow, I'm very new to C# and OOP but I actually knew that and missed it. Thank you, and Thank you all for your response. – hjavaher Jan 18 '13 at 03:15

score 2 · Answer 2 · answered Jan 18 '13 at 03:09

2

Your lists are null at this point. So

_vm.Monday

..will throw an exception. You have to new them up in the constructor:

public HoursOfOperation() {
    Monday = new List<DayTimes>();
    // ...etc
}

answered Jan 18 '13 at 03:09

Simon Whitehead

57,414
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93
127

score 0 · Answer 3 · answered Jan 18 '13 at 03:08

0

The various List properties are not being initialised; you need to add

_vm.Monday = new List<DayTime>();

answered Jan 18 '13 at 03:08

RJ Lohan

6,257
3
30
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score 0 · Answer 4 · answered Jan 18 '13 at 03:09

You need to create instances of the lists of day times:

var hoursOfOperation = new HoursOfOperation
{
   Monday = new List<DayTimes>(),
   Tuesday = new List<DayTimes>(),
   Wednesday = new List<DayTimes>(),
   Thursday = new List<DayTimes>(),
   Friday = new List<DayTimes>(),
   Saturday = new List<DayTimes>(),
   Sunday = new List<DayTimes>()
};

What's wrong with the following method call?

4 Answers4