Question

I know this has been asked a few times before, but the existing solutions look like hacks rather than a proper pattern.

I have a simple drop down list. I am trying to populate it with data and have a item pre selected. I am succeeding at the ‘populate it with data part’ but failing to get my preferred item pre-selected.

I am using ASP.NET MVC 3 RC2.

The important code bits:

{
    // Bunch of code
    CategoryOptions = new SelectList(categories, "Id", "Slug", article.Category.Id);
}

Now… the CategoryOptions is being passed to the Html helper like so:

@Html.DropDownListFor(a => a.Category, Model.CategoryOptions)

I have looked at the values being passed into the helper and have confirmed that one of the items has the selected value set to true:

However, it is not reflecting in the Html being generated by the helper. None of the … tags have the selected=”selected” attribute.

I used Reflector to examine the code a bit, and this line (SelectExtensions.SelectInternal) looks dicey:

item.Selected = (item.Value != null) ? set.Contains(item.Value) : set.Contains(item.Text);

Am I doing something wrong here? Or is the framework (ASP.NET MVC 3 RC2) at fault here.

Answer 1

Ok… I just fixed it.

I changed around my view model to use a CategoryId instead of a Category slug. So now, my view looks like:

@Html.DropDownListFor(a => a.CategoryId, Model.CategoryOptions, new { @class = "ask-category-field" })

I think the model value being select (in this case, a => a.CategoryId) has to have the same type as the selected ‘value.’ (I will refine this explanation when I get more time to go over the framework code.) But clever coding indeed 🙂 Hats of to ASP.NET MVC devs.

Now, it works perfectly as expect and also retains changes to the selected item across a PRG lifecycle.

Hope this helps someone.