MVC Controller throws null reference error

Question

On My DB context class I have code like this

  modelBuilder.Entity("WebApplication10.Data.JobCategory", b =>
            {
                b.Property<int>("ID")
                    .ValueGeneratedOnAdd();

                b.Property<string>("JobCategoryName");

                b.Property<int>("JobCategoryParentID");

                b.Property<string>("jobCategoryDetails");

                b.HasKey("ID");

                b.ToTable("JobCategory");
            });

And on my controller

 private readonly ApplicationDbContext _context;

    public IActionResult Index()
    {
        return View( _context.JobCategory.ToList());
    }

but on my controller class I get an error like this

An exception of type 'System.NullReferenceException' occurred in WebApplication10.dll but was not handled in user code

Additional information: Object reference not set to an instance of an object. Can anyone point out what i am doing wrong?

put a breakpoint and inspect your variables(Ex:_context) and see whether it (or a property which you are accessing) is null — Shyju, Jul 05 '16 at 20:17
suggestion: Practice placing debug point, in order to debug issues.It helps a lot and some time solution is in the error itself. .net framework is very smart, and uses meaningful names. — Saket Choubey, Jul 05 '16 at 20:27

user3378165 · Accepted Answer · 2016-07-06T05:03:22.523

1

It seems like your _context variable has never been initialized so how can you access its JobCategory property?

The runtime throwing a NullReferenceException always means the same thing: you are trying to use a reference. The reference is not initialized (or it was initialized, but is no longer initialized).

This means the reference is null, and you cannot access members through a null reference. The simplest case:

string foo = null;
foo.ToUpper();

This will throw a NullReferenceException at the second line, because you can't call the instance method ToUpper() on a string reference pointing to null.

Initial your variable like this:

private readonly ApplicationDbContext _context = new ApplicationDbContext();

edited Jul 06 '16 at 05:03

answered Jul 05 '16 at 20:19

user3378165

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Can you show me, How I could make that? – None Jul 05 '16 at 20:29
I edited my question. – user3378165 Jul 06 '16 at 05:13
Thanks, But I have already done this before like this private readonly ApplicationDbContext _context; But its still not working – None Jul 06 '16 at 17:50
Have you added the initialization part: `= new ApplicationDbContext()`? – user3378165 Jul 06 '16 at 20:50

MVC Controller throws null reference error

1 Answers1