Get "Object reference not set to an instance" when trying to add element to list

Question

I have a created this model;

namespace gantt.Models
{
    public class ganttModels
    {
        public IList<ganttModel> allGantt { get; set; }

    }

    public class ganttModel
    {
        public string projectName { get; set; }
        public IEnumerable<ResourcesSet> rescource { get; set; }
    }
}

Now my plan is to add items to this model, i have done this in a repository like this;

namespace gantt.Models
{
    public class GantDataRepository
    {
        GantEntities dbContext = new GantEntities();
        ganttModels returnModels = new ganttModels();
        ganttModel tempganttModel = new ganttModel();

        public GantDataRepository()
        {
            foreach (var item in dbContext.WorkPlans)
            {
                tempganttModel.projectName = item.Product;
                tempganttModel.rescource = item.ResourcesSets;
                returnModels.allGantt.Add(tempganttModel);   // Here i get the error     
            }   
        }

        public ganttModels getGant()
        {
            return returnModels;
        }    
    }
}

The repositor finds the data and add it. As i see it i have instansiate the returnModels already

but dont it fall under "returnModels"? Do i have to instansiate all the underlaying variables in a class? — Tim
– Tim, Commented Apr 18, 2013 at 11:22
@Tim Yes you do. The default value for reference types is null. Interfaces, as well as classes and delegates, are declared as reference types. — Conrad Clark
– Conrad Clark, Commented Apr 18, 2013 at 11:28
Arun, for 2-3 hours, im sorry but im pretty new to this world and all i could find on the matter was to instansiate it.And i do admit im abit ashamed. — Tim
– Tim, Commented Apr 18, 2013 at 11:37

Conrad Clark · Accepted Answer · 2013-04-18 11:21:56Z

9

returnModels is initialized.

returnModels.allGantt is not.

You can do this:

public class ganttModels
{
    public IList<ganttModel> allGantt { get; set; }
    public ganttModels()
    {
        allGantt = new List<ganttModel>();
    }
}

Or something.

answered Apr 18, 2013 at 11:21

Conrad Clark

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1 Comment

Tim Over a year ago

Ah, i see.. Sorry... This was really stupid of me, i stared myself blind on the main datatype :/

Prabhu Murthy · Accepted Answer · 2013-04-18 11:23:42Z

1

You are not instantiating your list inside ganttModels Class.

public class ganttModels
{
    public ganttModels(){
      allGantt = new List<ganttModel>();      
    }

    public IList<ganttModel> allGantt { get; set; }

}

answered Apr 18, 2013 at 11:23

Prabhu Murthy

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Comments

James Kyburz · Accepted Answer · 2013-04-18 11:23:57Z

1

returnModels.allGantt in null when you try to add to it.

Either creat an instance of List in the constructor of gantModels or

prior to the Add call

returnModels.allGantt = new List<gantModel>();

answered Apr 18, 2013 at 11:23

James Kyburz

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Community · Accepted Answer · 2017-05-23 12:23:37Z

1

You can either define a constructor as Conrad has it in the answer, or you can get rid of auto implemented property and do:

private IList<ganttModel> _allGantt = new List<ganttModel>();

public IList<ganttModel> AllGantt
{
    get { return _allGantt; }
    set { _allGantt = value; }
}

edited May 23, 2017 at 12:23

CommunityBot

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answered Apr 18, 2013 at 11:25

Habib

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Comments

Trevor Pilley · Accepted Answer · 2013-04-18 11:27:09Z

You need to define your ganttModels class as follows:

public class GanttModels // use correct casing!
{
    public GanttModels() { this.AllGantt = new List<GanttMode>(); }
    public IList<GanttModel> AllGantt { get; private set; }
}

You are also re-using the same reference in your repository so you should do this instead:

public class GantDataRepository
{
    GantEntities dbContext = new GantEntities();
    GanttModels returnModels = new GanttModels();

    public GantDataRepository()
    {
        foreach (var item in dbContext.WorkPlans)
        {
            returnModels.AllGantt.Add(new GanttModel 
            {
                ProjectName = item.Product,
                Rescource = item.ResourcesSets
            });
        }
    }

A.T. · Accepted Answer · 2013-04-20 09:08:55Z

0

you need to initilize allGantt....

    private IList<ganttModel> _allGantt;
    public IList<ganttModel> allGantt { 
          get{ return _allGantt ?? (_allGantt = new new List<ganttModel>()); } 
          set{ _allGantt = value;} 
     }

edited Apr 20, 2013 at 9:08

answered Apr 18, 2013 at 11:31

A.T.

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