Appending values to list of class inside viewmodel

Question

I need to append values to a list of Class Category.

I have tried several combinations including appending 1 row at the time or append a range.

marticle.ListOfCategories.Add(crow); THiS DID NOT WORK
  // marticle.ListOfCategories(ccarticle); THiS DID NOT WORK

I get the following error:

Object reference not set to an instance of an object.

Here is my category class:

public class Category
{
    public int ID { get; set; }

    [Required]
    public string Title { get; set; }
}

And here is my view model

public class ArticleEditViewModel
    {
        public int ID { get; set; }

        [Required]
        public Boolean Active { get; set; }

        [Required]
        public string Title { get; set; }

        public List<Category> ListOfCategories { get; set; }
    }

And here is my recordset append(s) plural

 public ArticleEditViewModel ArticleSelectById(int? id)
        {
            ArticleEditViewModel marticle = new ArticleEditViewModel();
            string connString =
                System.Configuration.ConfigurationManager.ConnectionStrings["mydb"].ConnectionString;
            using (SqlConnection conn = new SqlConnection(connString))
            {
                conn.Open();
                using (SqlCommand cmd = new SqlCommand())
                {
                    cmd.Connection = conn;
                    cmd.CommandType = System.Data.CommandType.StoredProcedure;
                    cmd.CommandText = "content.Article_Select_ById";
                    cmd.Parameters.Add("@ID", SqlDbType.Int).Value = id;
                    using (SqlDataReader rdr = cmd.ExecuteReader())
                    {
                        while (rdr.Read())
                        {
                            if (rdr["ID"] != DBNull.Value)
                            {
                                marticle.ID = Convert.ToInt32(rdr["ID"]);
                            }
                            if (rdr["Title"] != DBNull.Value)
                            {
                                marticle.Title = rdr["Title"].ToString();
                            }                            
                        }
                    }
                }
                conn.Close();

                //Append the list of categories

                 List<Category> ccarticle = new List<Category>();
                conn.Open();
                using (SqlCommand cmd = new SqlCommand())
                {
                    cmd.Connection = conn;
                    cmd.CommandType = System.Data.CommandType.StoredProcedure;
                    cmd.CommandText = "dbo.Category_SelectAllActive";

                    using (SqlDataReader rdr = cmd.ExecuteReader())
                    {
                        while (rdr.Read())
                        {
                            Category crow = new Category();
                            if (rdr["ID"] != DBNull.Value)
                            {
                                crow.ID= Convert.ToInt32(rdr["ID"]);
                            }
                            if (rdr["Description"] != DBNull.Value)
                            {
                                crow.Description = rdr["Description"].ToString();
                            }
                            crow.Active = true;
                            ccarticle.Add(crow);
                            marticle.ListOfCategories.Add(crow); //THiS DID NOT WORK
                        }
                    }
                }
               // marticle.ListOfCategories(ccarticle); THiS DID NOT WORK
            }
            return marticle;
        }

Matt Bodily · Accepted Answer · 2014-05-28 01:11:03Z

2

you don't show what crow as defined as. Here is a short hand way of adding it

marticle.ListOfCategories.Add(new Category() { ID = YourID, Title = YourTitle });

just replace yourid and yourtitle with your database values. Since it is a list of Class you need to define an object of that type and add that to the list.

Edit:

before setting a list you need to initialize it

marticle.ListOfCategories = new List<Category>();

I would recommend setting this in a constructor in your class

public ArticleEditViewModel(){
    ListOfCategories = new List<Category>();
}

this way everytime you create a new instance of your viewmodel the list will be automatically initialized

Edit2:

the constructor goes in the class like this

public class ArticleEditViewModel
{
    public ArticleEditViewModel(){
        ListOfCategories = new List<Category>();
    }
    public int ID { get; set; }

    [Required]
    public Boolean Active { get; set; }

    [Required]
    public string Title { get; set; }

    public List<Category> ListOfCategories { get; set; }
}

edited May 28, 2014 at 1:11

answered May 28, 2014 at 0:31

Matt Bodily

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4 Comments

Internet Engineer Over a year ago

Sure I do. CROW is defined as Category crow = new Category();

Internet Engineer Over a year ago

I tried your solution and it gives me the same error: Object reference not set to an instance of an object.

Internet Engineer Over a year ago

There is one problem with this solution. Now ListOfCategories is not accessible in the view....

Matt Bodily Over a year ago

I put the constructor in your class so you can see what it looks like together. let me know if you have any questions.

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