更改MVC SelectList选择的值

Question

SelectList dropdown = DropDown;
foreach (var item in dropdown)
    {
     var modelValue = property.GetValue(Model.FormModel);
     if (String.Equals(item.Value, modelValue))
              {
                   item.Selected = true;
                   System.Diagnostics.Debug.WriteLine(item.Selected);
               }
     }

foreach (var item in dropdown)
      {
       var modelValue = property.GetValue(Model.FormModel);
       if (String.Equals(item.Value, modelValue))
             {
                    System.Diagnostics.Debug.WriteLine(item.Selected);
              }
       }

Logically, the code above should output either nothing or true, true unless magic magnetic fields are changing bits in the computer between one foreach loop and the other.

And yet, I get true, false . How is this even remotely possible? With the debugger, I saw 'item' gets correctly parsed and item.Selected = true gets correctly called on the item I'd like. The second loop is just for debugging purpose.

---

this is how I build the DropDown. I can't touch this code as the dropdown returned should always be generic.

var prov = (from country in Service.GetCountries()
         select new
          {
           Id = country.Id.ToString(),
           CountryName = Localizator.CountryNames[(CountryCodes)Enum.Parse(typeof(CountryCodes), country.Code)],
           }).Distinct().ToList().OrderBy(l => l.CountryName).ToList();
           prov.Insert(0, new { Id = String.Empty, CountryName = Localizator.Messages[MessageIndex.LabelSelectAll] });
  _customerCountrySelectionList = new SelectList(prov, "Id", "CountryName");

Answer 1

if you iterate through a collection using foreach you can not modify its contents. therefore the 2nd iteration will access the same unmodified list...

use Linq to create a list of "SelectListItems" directly and then assign that list to the dropdownhelper

from x in y where ... select new SelectListItem { value = ..., text = ..., selected = ... }

using your code... you might want to create something like

var modelValue = property.GetValue(Model.FormModel);
IEnumerable<SelectListItem> itemslist = 
         (from country in Service.GetCountries()
          select new SelectListItem {
          {
            value = country.Id.ToString(),
            text  = Localizator
                      .CountryNames[
                          (CountryCodes)Enum
                                         .Parse(typeof(CountryCodes),
                          country.Code)
                       ],
            selected = country.Id.ToString().Equals(modelValue)
           }).Distinct().ToList().OrderBy(l => l.text);

... havent tested that in VS though, so play around with it and see if you can get it to work

Answer 2

item.Selected = true; is set to true on first loop.