System.ArgumentNullException: Value cannot be null. Parameter name: source

Question

here my code is its showing the parameter you have passed is null:-

[HttpPost]
public String Indexhome( IEnumerable<Seat>  Seats )
{
     if (Seats.Count(x => x.IsSelected) == 0)
     {
            return "you didnt select any seats";
     }
     else
     {
           StringBuilder sb = new StringBuilder();
           sb.Append("you selected");
           foreach (Seat seat in Seats)
           {
               if (seat.IsSelected)
               {
                   sb.Append(seat.Name + " ,");
               }
            }
           sb.Remove(sb.ToString().LastIndexOf(","), 1);
           return sb.ToString();
     }   
}

MakePeaceGreatAgain · Answer 1 · 2016-10-20T08:46:02.540

The exception appears because - as Lucero already mentions - Seats is null. In contrast to a usual method you don´t get a NullReferenceException here because Count is an extension-method:

public static int Count(this IEnumerable<T> source)
{
    if (source == null) throw new ArgumentNullException("source");
}

So as you see the method throws an ArgumentNullException instead of a NullReferenceException if source is null.

As an aside don´t use Count to check if your collection has items, use Any instead, as it doesn´t enumerate the complete collection and returns when the very first matching the condition was found.

EDIT: If You´d about to use another method which is a normal instance-method you´d get an NRE however:

Seats.DoSomething(); // throws NRE when Seats = null

So check if the argument is null before using it:

[HttpPost]
public String Indexhome( IEnumerable<Seat>  Seats )
{
    if (Seats == null || !Seats.Any(x=> x.IsSelected))
        return "you didnt select any seats";
}

Lucero · Accepted Answer · 2016-10-20T08:42:14.063

2

Seats will be null if you call the method without matching data / query argument. You need to also check that, like so for instance:

[HttpPost]
public String Indexhome( IEnumerable<Seat>  Seats )
{
     if ((Seats == null) || !Seats.Any(s => s.IsSelected))
     {
            return "you didnt select any seats";
     }
     else
     {
           return "you selected " + string.Join(", ", Seats.Where(s => s.IsSelected).Select(s => s.Name));
     }   
}

edited Oct 20 '16 at 08:42

answered Oct 20 '16 at 08:22

Lucero

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Yup its shows you didn't select any seats while m selecting seats !! – Debashish Dwivedi Oct 20 '16 at 08:49
@DebashishDwivedi Yes, you need to check the format of the data you're sending, it doesn't match. – Lucero Oct 20 '16 at 08:51
I am selecting seats bt its showing u didnt select any seats – Debashish Dwivedi Oct 20 '16 at 08:55
actually IsSelected is boolean type value – Debashish Dwivedi Oct 20 '16 at 08:57
@DebashishDwivedi Yes I got that... but since you don't show how and what data you send to the controller it's impossible to tell where the problem is on the client side. The data binder doesn't find the "Seats" in the data posted - way before it tries to deserialize. I suggest you open *another question* with the client-side code and show the data sent to the server (you can get this through the developer console network tab). – Lucero Oct 20 '16 at 08:58
okay thanks @lucero – Debashish Dwivedi Oct 20 '16 at 09:02
this my view page – Debashish Dwivedi Oct 20 '16 at 09:35

System.ArgumentNullException: Value cannot be null. Parameter name: source

2 Answers2