MVC4 binding drop down list in a list (bug)

问题

I have the below code in a view. (index.cshtml)

Binding Problem

The first drop down selects the correct value, based on the 'ChildItem' editor template.
The second example using an inline drop down list does not work I don't want to create an editor template just to display drop down values.
The odd thing is that TextBoxFor will show the correct value. This seems to be an issue just with the drop down list.

How do I fix the binding so that the second drop down works? I debugged it. It would appear that ViewData.Eval is not picking up the correct value from _.Children[i].ChooseId.

Update (bug)
This is a confirmed bug (low priority, how?) in the MVC framework http://aspnet.codeplex.com/workitem/8311

@using (Html.BeginForm())
{
    for (int i = 0; i < Model.Children.Count(); i++)
    {
       <p>A: @Html.EditorFor(_ => _.Children[i], "ChildItem")</p>
       <p>B: @Html.DropDownListFor(_ => _.Children[i].ChooseId, TestModel.PeopleSelect)</p>
    }
    <button type="submit">GO</button>
}

I have tried using DropDownListFor(_ => Model.Children[i].ChooseId), same result.
using TextBoxFor(_ => _.Children[i].ChooseId) shows the correct value, wierd?

For reference here is ChildItem.cshtml

@using dropdown.Controllers
@using dropdown.Models
@model dropdown.Models.TestPerson
@Html.DropDownListFor(_ => _.ChooseId, TestModel.PeopleSelect)

It looks like this:

回答1:

I have subsequently found this: http://aspnet.codeplex.com/workitem/8311 It's a confirmed bug.

The only workaround i have found is this.

Mark Selected Item

@Html.DropDownListFor(_ => _.Children[i].ChooseId, Mark(TestModel.PeopleSelect, Model.Children[i].ChooseId))

Mark Function / Extension Method

@functions {
    private IEnumerable<SelectListItem> Mark(IEnumerable<SelectListItem> items, object Id)
    {
        foreach (var item in items)
            if (string.CompareOrdinal(item.Value, Convert.ToString(Id)) == 0)
                item.Selected = true;
        return items;
    }
}

回答2:

You could put the items into a partial view and load that for your child objects, OR...

You could opt to do a foreach loop on the child collection, and use it like this:

foreach (var itm in Model.Children)
{
    @Html.DropDownListFor(modelItem => itm.ChooseId,
          new SelectList( (IEnumerable<SelectListItem>)TestModel.PeopleSelect, "Value", "Text", itm.ChooseId),
          htmlAttributes: new { @class = "form-control" }
    )
}

This assumes that TestModel.PeopleSelect has been created as a SelectListItem[] or IEnumerable<SelectListItem>. Code to do that properly is in my answer on a related question: ASP.NET MVC4 Model's Child Collection Drop Down List not binding properly

Doing a for loop on the child collection gave me the error:

Cannot apply indexing with [] to an expression of type 'ICollection<Children>'

So I wouldn't recommend that.

来源：https://stackoverflow.com/questions/14951544/mvc4-binding-drop-down-list-in-a-list-bug

标签

asp.net-mvc

razor

binding

html.dropdownlistfor