MVC DropDownList lagging - asp.net-mvc

Question

I am posting the id of a dropdownlist back to the index (index2 view). but is lagging behind. After a second time pressing Select it shows me the correct list.
http://www.jeroenchristens.be/CountriesWorld
(the first page is only for showing the complete list, after selecting from the dropdownlist,, it gets to index2, a shorter list) And then after choosing another Selection from the dropdownlist, you have to try this twice each time.
I successfully copied this from the id the value and pass this on, why is it lagging behind.
Index2 Viewpage
#using System.Collections
#using System.Web.UI.WebControls
#model IEnumerable<CVtje.Models.Countries>
<h2>Index</h2>
#using (Html.BeginForm("Index2", "CountriesWorld", new { #id = Request.Form["SelectedContinent"] }, FormMethod.Post))
{
<div class="form-group">
#Html.DropDownList("SelectedContinent",
new SelectList((IEnumerable) ViewData["continentsList"], "Continent", "Continentomschrijving"))
<button type="submit" class="btn btn-primary">Select</button>
</div>
}
<table id="countriesworld" class="table table-active table-hover">
<thead>
<tr>
<th>Vlag</th>
<th>
Code
</th>
<th>
Land
</th>
<th>Continent</th>
</tr>
</thead>
#foreach (var item in Model)
{
<tr>
<td>
<img src="#string.Format("../../images/countries/{0}.png", item.Code)" width="25" HEIGHT="15" />
</td>
<td>
#item.Code
</td>
<td>
#item.Country
#*#Html.ActionLink("Details", "Index", "ReizensDetails", new { id = item.ReizenId }, null)*#
#*|
#Html.ActionLink("Details", "Details", new { id = item.Id }) |
<button data-myprofile-id="#item.Id" class="btn-link js-delete">Delete</button>*#
</td>
<td>#item.Continents.Continentomschrijving</td>
</tr>
}
</table>
my controller:
public ActionResult Index(int? id)
{
List<Continents> continentsList = new List<Continents>();
continentsList = _context.Continents.ToList();
ViewData["continentsList"] = continentsList;
var countriesWorld = _context.Countries.OrderBy(e => e.Country).ToList();
return View(countriesWorld);
}
[HttpPost]
public ActionResult Index2(int id)
{
//return View(db.MyProfiles.ToList());
List<Continents> continentsList = new List<Continents>();
continentsList = _context.Continents.ToList();
ViewData["SelectedContinent"] = id.ToString();
ViewData["continentsList"] = continentsList;
var countriesWorld = _context.Countries.Where(e => e.Continent == id).OrderBy(e => e.Country).ToList();
return View(countriesWorld);

Answer 1

You have added a route value using new { #id = Request.Form["SelectedContinent"] } in your BeginForm() method.
Assuming the initial value is 0, then it generates action = "/CountriesWorld/Index2/0". Lets assume you select the option with value="1" and you now post the form. The id attribute is bound to 0 and you filter the Countries based on .Where(e => e.Continent == 0) - no where have you ever used the value of the selected option which is bound to a non-existent property named SelectedContinent.
Now you return the view and the forms action attribute is now action = "/CountriesWorld/Index2/1" (because Request.Form["SelectedContinent"] is 1). If you select the option with value="2", the same thing occurs - you ignore the value of the selected option and the filter the Countries based on .Where(e => e.Continent == 1) because the id parameter is 1.
Always bind to a model, which in your case will be
public class CountriesVM
{
public int? SelectedContinent { get; set }
public IEnumerable<SelectListItem> ContinentsList { get; set; }
public IEnumerable<Country> Countries { get; set; }
}
and in the view, strongly bind to your model (note the FormMethod.Get and the 3rd parameter in DropDownListFor())
#model CountriesVM
#using (Html.BeginForm("Index", "CountriesWorld", FormMethod.Get))
{
#Html.DropDownListFor(m => m.SelectedContinent, Model.ContinentsList, "All")
<button type="submit" class="btn btn-primary">Select</button>
}
<table ... >
....
#foreach(var country in Model.Countries)
{
....
}
</table>
and you need only one method
public ActionResult Index(int? selectedContinent)
{
var countries = _context.Countries.OrderBy(e => e.Country);
if (selectedContinent.HasValue)
{
countries = countries.Where(e => e.Continent == selectedContinent.Value);
}
continentsList = _context.Continents.Select(x => new SelectListItem
{
Value = x.Continent.ToString(),
Text = x.Continentomschrijving
});
var model = new CountriesVM
{
SelectedContinent = selectedContinent,
ContinentsList = continentsList,
Countries = countries
};
return View(model);
}
Note you might also want to consider caching the Continents to avoid repeated database calls assuming they do not change often (and invalidate the cache if their values are updated)