Problems with DropdownList ASP.net MVC5

Question

I'm having so much problems for this basic thing in regards to dropdownlist I did so many methods described in stackoverflow and all didn't work I will sum the code like this. I just want to simple create a dropdownlist that is saved to the database.

Here is what I did DefaultModel

public class DefaultModel
  {
    public int Id {get; set;}
    //other things
    public CountryList SelectedCountry {get; set;}
  }
  public DefaultDbContext : DbContext
   {
      public DbSet<DefaultModel> DefaultModels {get; set;}
      public DbSet<CountrtyList> CountryLists {get; set;}
   }

CountryList Model

public class CountryList
  {
    public byte Id {get; set;}
    public string name {get; set;} //country name
    public DefaultModel DefaultModel {get; set;}
  }

ViewModel

 public class CountryListViewModel
 {
   public byte Id {get; set;}
   public List<CountryList> CountryList {get; set;}

DefaultController Not Home Controller

 private DefaultDbContext = db;
 public HomeController
 {
   db = new DefaultDbContext;
 }

 public ActionResult Index()
  {
        var countryLists= _context.CountryLists.ToList();
        var viewModel = new CountryListViewModel
        {
            Default = new DefaultModel(),
            CountryLists = countrylists
        };

        return View(viewModel);
  }

View

 @model Default.ViewModels.CountryListViewModel
 <div class="form-group">
 @Html.LabelFor(model => 
  model.TransactionModel.SelectedCountry.CountryLists
   , new { @class = "control-label col-md-2" })
    <div class="col-md-10">
   @Html.DropDownListFor(
   model =>    model.TransactionModel.SelectedCountry.CountryLists
   , new     SelectList(Model.CountryList, "Id, Name"), "Select Country")
    </div>
</div>
 <div class="form-group">
    <div class="col-md-offset-2 col-md-10">
        <input type="submit" value="Create" class="btn btn-default" />
    </div>
</div>

Migration adding Countries

 Sql("INSERT INTO COUNTRYLISTS (Id, Name) VALUES(1, UK)");

Error

System.NullReferenceException: 'Object reference not set to an instance of an object.'

I'm just trying to learn how to create a dropdownlist in MVC5 from scratch and I wasted allot of hours & constantly failing at multiple attempts. I see tutorials that use ways that simply don't work I have no idea what is wrong or what I should do.

Answer 1

Modal

namespace WebApp.Models
{
    public class CountryList
    {
        public byte Id { get; set; }
        public string name { get; set; } //country name
        //public DefaultModel DefaultModel { get; set; }
    }
    public class CountryListViewModel
    {
        public string CountryLists { get; set; }
        public List<CountryList> CountryList { get; set; }
    }
}

Controller

`

        List<CountryList> countrylists = new List<CountryList>();

        //I am using static list items. Just change this to get data from entity framework;

        countrylists.Add(new CountryList  //pass one default list Item here so that your list is never null.
        {
            Id = 0,
            name = "Select Country"
        });

        countrylists.Add(new CountryList
        {
            Id = 1,
            name = "UK"
        });
        var viewModel = new CountryListViewModel
        {
            //Default = new DefaultModel(),
            CountryList=countrylists,
            CountryLists="Country List"
        };

        return View(viewModel);`

View

<div class="content">
    @Html.LabelFor(model => model.CountryList, new { @class = "control-label col-md-2" })

    <div class="col-md-10">

        @Html.DropDownListFor(model => model.CountryList, new SelectList(Model.CountryList, "id", "name"))

    </div>

    <br />
    <br />
    <br />
    <a href="http://helpmepal.org">Help Me Pal</a>
</div>