List of object is null even after calling constructor

Question

I have the following viewmodel with a constructor:

public class ActivitiesReportViewModel
{

    public ActivitiesReportViewModel()
    {
        List<ActivityType> ActivityTypeList = new List<ActivityType>();
        List<Activity> ActivityList = new List<Activity>();
        List<Client> ClientList = new List<Client>();
        List<List<ActivityCounter>> ActivityCounterList = new List<List<ActivityCounter>>();
    }

    [DisplayName("Responsável")]
    public string UserName { get; set; }

    [DisplayName("Data Inicial")]
    [Required]
    public DateTime DateFrom { get; set; }

    [DisplayName("Data Final")]
    [Required]
    public DateTime DateTo { get; set; }

    [DisplayName("Tipos de Atividade")]
    public virtual List<ActivityType> ActivityTypeList { get; set; }

    [DisplayName("Atividades")]
    public virtual List<Activity> ActivityList { get; set; }

    [DisplayName("Clientes")]
    public virtual List<Client> ClientList { get; set; }

    public List<List<ActivityCounter>> ActivityCounterList { get; set; }

}

And my ActionResult:

 public ActionResult ActivityReport()
    {
      var model = new ActivitiesReportViewModel();
      return View(model);
    }

But after initializing model, all lists are null as bellow:

I debugged the execution of the code and seems like the constructor is being correctly called, I just can't understand why all lists are still null after this.

I'm new to C#, so maybe I'm just missing something basic here and will be very grateful for any help you could provide.

Thank you in advance.

Ps: the problem with this situation is that I get a null refference exception because my lists are null when used in my view.

Hello techspider! All lists will be populated after the user sets the filters in my view and submit it to the other ActionResult ( ActionResult ActivityReport(ActivitiesReportViewModel model)). In this case I just want to show the view with no data on it. Thanks! — Diego Gomes Santos, May 09 '16 at 19:51

score 3 · Accepted Answer · answered May 09 '16 at 19:49

3

You're declaring new local variables in the constructor and assigning to them, not to the properties in your class.

Change the constructor to:

public ActivitiesReportViewModel()
{
    ActivityTypeList = new List<ActivityType>();
    ActivityList = new List<Activity>();
    ClientList = new List<Client>();
    ActivityCounterList = new List<List<ActivityCounter>>();
}

Duplicate names like that is allowed, but can make things confusing.

answered May 09 '16 at 19:49

Chris

5,442
17
30

Thank you Chris, you were right. It is working now. – Diego Gomes Santos May 09 '16 at 19:54

score 0 · Answer 2 · answered May 09 '16 at 19:47

0

You've not assigned any values within your constructor. You need to add another constructor with all your fields and then assign them. Then add the fields in your instantiation

answered May 09 '16 at 19:47

TechnicalTophat

1,655
1
15
37

score 0 · Answer 3 · answered May 09 '16 at 19:47

Your initialization is wrong. You are creating another variable instead of instantiating instance members

    public class ActivitiesReportViewModel
{

    public ActivitiesReportViewModel()
    {
        ActivityTypeList = new List<ActivityType>();
        ActivityList = new List<Activity>();
        ClientList = new List<Client>();
        ActivityCounterList = new List<List<ActivityCounter>>();
    }

    [DisplayName("Responsável")]
    public string UserName { get; set; }

    [DisplayName("Data Inicial")]
    [Required]
    public DateTime DateFrom { get; set; }

    [DisplayName("Data Final")]
    [Required]
    public DateTime DateTo { get; set; }

    [DisplayName("Tipos de Atividade")]
    public virtual List<ActivityType> ActivityTypeList { get; set; }

    [DisplayName("Atividades")]
    public virtual List<Activity> ActivityList { get; set; }

    [DisplayName("Clientes")]
    public virtual List<Client> ClientList { get; set; }

    public List<List<ActivityCounter>> ActivityCounterList { get; set; }

}

mihkov · Answer 4 · 2016-05-09T19:56:07.353

0

public ActivitiesReportViewModel()
{
    this.ActivityTypeList = new List<ActivityType>();
    this.ActivityList = new List<Activity>();
    this.ClientList = new List<Client>();
    this.ActivityCounterList = new List<List<ActivityCounter>>();
}

You are forgot to initialize your properties.

edited May 09 '16 at 19:56

answered May 09 '16 at 19:49

mihkov

1,171
13
37

I know using always `this` keyword is better practice. Or maybe it's only my preference – mihkov May 09 '16 at 19:53
While this answer solves the problem, a good answer also includes explanation about what is wrong. That being said: this type of issue is so incredibly common that you shouldn't do all that and instead just flag the question as a duplicate of the canonical Q&A on the topic. – Jeroen Vannevel May 09 '16 at 19:53

List of object is null even after calling constructor

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