DropDownListFor in EditorTemplate not selecting value

Solution 1:

We also solved the solution by populating a new SelectList that has the appropriate SelectListItem selected, but created this extension method to keep the call to DropDownListFor a little cleaner:

public static SelectList MakeSelection(this SelectList list, object selection)
{
    return new SelectList(list.Items, list.DataValueField, list.DataTextField, selection);
}

Then your DropDownListFor call becomes:

<%= Html.DropDownListFor(m => m.DocumentCategoryType, Model.DocumentCategoryTypeList.MakeSelection(Model.DocumentCategoryType)) %>

Solution 2:

Looking through the ASP.NET MVC 2 source code reveals some solutions to this problem. Essentially, any SelectListItem in the SelectList passed in the helper extension method that has the Selected property set to true does not have any bearing over the <option> element rendered with the selected attribute applied for the item.

The selected attribute on <option> elements is determined by

1) checking that the helper extension method was passed a SelectList. If this is null, the framework will look in the ViewData for a value corresponding to the key that is the view model property for which you wish to render the drop down list for. If the value is a SelectList, this will be used to render the <select> including taking any selected values, so long as the model state for the model property is null.

2) If a SelectList has been passed in the helper extension method and the model state for the model property is null, the framework will look in the ViewData for a default value, using the model property name as the key. The value in view data is converted to a string and any items in the SelectList passed to the helper extension method that have a value (if no value is set, then the Text will be checked) that matches the default value will have the Selected property set to true which in turn will render an <option> with the attribute selected="selected".

Putting this together, there are two plausible options that I can see to have an option selected and use the strongly typed DropDownListFor:

Using the following view model

public class CategoriesViewModel
{
    public string SelectedCategory { get; private set ; }
    public ICollection<string> Categories { get; private set; }

    public CategoriesViewModel(string selectedCategory, ICollection<string> categories)
    {
        SelectedCategory = selectedCategory;
        Categories = categories;
    }
}

Option 1

Set a value in the ViewData in the controller rendering your view keyed against the property name of the collection used to render the dropdown

the controller action

public class CategoriesController
{
    [HttpGet]
    public ViewResult Select()
    {
        /* some code that gets data from a datasource to populate the view model  */
        ICollection<string> categories = repository.getCategoriesForUser();
        string selectedCategory = repository.getUsersSelectedCategory();

        CategoriesViewModel model = new CategoriesViewModel(selectedCategory, categories);
        this.ViewData["Categories"] = selectedCategory;        

        return View(model);
    }

    [HttpPost]
    public ActionResult Select(CategoriesViewModel model)
    {
        /* some code that does something */
    }
}

and in the strongly typed view

<%: Html.DropDownListFor(m => m.Categories, Model.Categories.Select(c => new SelectListItem { Text = c, Value = c }), new { @class = "my-css-class" }) %>

Option 2

Render the dropdown using the name of the property of the selected item(s)

the controller action

public class CategoriesController
{
    [HttpGet]
    public ViewResult Select()
    {
        /* some code that gets data from a datasource to populate the view model  */
        ICollection<string> categories = repository.getCategoriesForUser();
        string selectedCategory = repository.getUsersSelectedCategory();

        CategoriesViewModel model = new CategoriesViewModel(selectedCategory, categories);

        return View(model);
    }

    [HttpPost]
    public ActionResult Select(CategoriesViewModel model)
    {
        /* some code that does something */
    }
}

and in the strongly typed view

<%: Html.DropDownListFor(m => m.SelectedCategory, Model.Categories.Select(c => new SelectListItem { Text = c, Value = c }), new { @class = "my-css-class" }) %>

Solution 3:

It is confirmed as a bug @ aspnet.codeplex.com and only behaves like this for strongly typed views.

Workaround: populate your SelectList in the view code

<%= Html.DropDown("DocumentCategoryType", new SelectList(Model.Categories,"id","Name",Model.SelectedCategory")) =>

Solution 4:

Yuck. I ended up solving it like this. I hope this gets fixed for RTM.

   <%if(Model!=null){ %>
        <%= Html.DropDownListFor(m => m.DocumentCategoryType, new SelectList(Model.DocumentCategoryTypeList,"Value","Text", Model.DocumentCategoryType))%>
        <%}else{%>
            <%=Html.DropDownListFor(m => m.DocumentCategoryType, Model.DocumentCategoryTypeList) %>
        <%}%>

Solution 5:

Make sure you have a value assigned to m.DocumentCategoryType when you send it to the view.

Generally this value will get reset when you do a post back so you just need to specify the value when returning to your view.

When creating a drop down list you need to pass it two values. 1. This is where you will store the selected value 2. Is the actual List

Example

<%=Html.DropDownListFor(m => m.DocumentCategoryType, Model.DocumentCategoryTypeList) %>

I made the mistake of setting the select list item Selected value to True. This won't do anything. Instead just assign a value to m.DocumentCategoryType in your controller and this will actually do the selection for you.