CODEWITHSUNDEEP
c#asp.net-mvcmodel-bindinghtml.dropdownlistfor
janhartmann
janhartmann

Reputation: 15003

Using DropDownList(For) with model binding on nested class

I am relying heavily on EditorTemplates in my application, but I've run into a problem which I can not seem to solve, without not moving away from EditorTemplates for drop down lists.

Consider this (View)Model:

public class CreateStudentViewModel
{
    public DropDownList StudentTypes { get; set; }
    public CreateStudent Command { get; set; }
}

public class DropDownList {
    public string SelectedValue { get; set; }
    public IList<SelectListItem> Items { get; set; }
}

public class CreateStudent {
    public string Name { get; set; }
    public int StudentTypeId { get; set; }
}

I use this to provide a way for the frontend user to set the student type, this is done with the following EditorTemplate:

@model DropDownList
<div class="form-group@(Html.ValidationErrorFor(m => m.SelectedValue, " has-error"))">
    @Html.LabelFor(m => m)
    @Html.DropDownListFor(m => m.SelectedValue, Model.Items)
    @Html.ValidationMessageFor(m => m.SelectedValue, null)
</div>

And used within my view:

@Html.EditorFor(m => m.StudentTypes)

Now this EditorTemplate is binding to the StudentTypes.SelectedValue on DropDownList, which is good in some cases - but I need to bind this to my Model.Command.StudentTypeId here.

I know I can move all this code directly to the view and directly bind it, instead of having it inside a EditorTemplate, but I will try my best to avoid this.

Ideally I am thinking of extending the EditorFor to provide a way like:

@Html.EditorFor(m => m.StudentTypes, new { selectedValue = Model.Command.StudentTypeId });

But I can not seem to translate this to something like:

@Html.DropDownList(@ViewBag.selectedValue.ToString(), Model.Items);

As this just places the value (int) as the field name. Any suggestions is welcome! :-)

Upvotes: 1

Views: 1454

Answers (1)

Chris Pratt
Chris Pratt

Reputation: 239430

Your chief problem here is encapsulating your drop down list in a class in order to rely on the C# type editor template convention. Instead, just use your model directly and use UIHint to tell Razor to use a particular template. Here's a simplified version of what I use:

View Model

[UIHint("Choice")]
public int SelectedFoo { get; set; }

public IEnumerable<SelectListItem> FooChoices { get; set; }

Views\Shared\EditorTemplates\Choice.cshtml

@{
    var choices = ViewData["choices"] as IEnumerable<SelectListItem> ?? new List<SelectListItem>();

    if (typeof(System.Collections.IEnumerable).IsAssignableFrom(ViewData.ModelMetadata.ModelType) && ViewData.ModelMetadata.ModelType != typeof(string))
    {
        @Html.ListBox("", choices)
    }
    else
    {
        @Html.DropDownList("", choices)
    }
}

View

@Html.EditorFor(m => m.SelectedFoo, new { choices = Model.FooChoices })

In case it's not obvious, the conditional in the editor template determines if the property is a value or list type, and either uses a drop down list control or listbox control, respectively.

Upvotes: 1

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