Question

Based on Darin’s answer to my question Ho to display multiple checkbox selection based on user's selection from dropdown?
I am displaying multiple checkboxes based on dropdown selection.

Now, once the user post the form (with multiple inputs) that i have on my page, i collect all the data using FormCollection. And the problem i have is how can i pull those selected checkbox values from formcollection? The number of checkbox will change on different selection from the drop-down, so i think requesting each checkbox value will not work.

Can anyone help me with this problem.

The flow is as shown below:

Properties in Model

public class Subcategory
{
    public string Name { get; set; }
    public int ID { get; set; }
    public bool Flag { get; set; }
}

Displaying PartialView in actual view where other form inputs are there:

 <div id="checkboxlist">
      @if (Model.SubCategories != null)
      {
           @Html.Partial("SubCategories", Model.SubCategories)
      }
 </div>    

PartialView SubCategories.cshtml

@model IEnumerable<MyProject.Entities.Subcategory>
@{
// we change the HTML field prefix so that input elements
// such as checkboxes have correct names in order to be able
// to POST the values back 
ViewData.TemplateInfo.HtmlFieldPrefix = "checkboxlist";
}
<span>subcategory</span>
<div id="subcategories" style="margin-left: 130px;margin-top: -20px;" data-role="fieldcontain">
   <fieldset data-role="controlgroup">
      @Html.EditorForModel()
   </fieldset>
</div> 

EditorTemplates Subcategory.cshtml

@model MyProject.Entities.Subcategory
<div class="editor-label">
   @Html.CheckBoxFor(c => c.Flag, new { type = "checkbox" })
   <label for="@Model.ID">@Model.Name</label>
   @Html.HiddenFor(c => c.Flag)
   @Html.HiddenFor(c => c.ID)
   @Html.HiddenFor(c => c.Name)
</div>

jquery to display checkboxes based on dropdown selection:

 $('#Category').change(function () {
    var subcategoriesUrl = $(this).data('subcategoriesurl');
    var categoryId = $(this).val();
    $('#checkboxlist').load(subcategoriesUrl, { category: categoryId });
 });

Answer 1

Don’t use FormCollection. That’s weakly typed. Use view models. Like this:

[HttpPost]
public ActionResult Foo(MyViewModel model)
{
    // model.BusinessSubCategories should contain a list of Subcategory
    // where for each element you could use the Flag property to see if
    // it was selected or not
    ...
}

Also notice that you have an inconsistency between the field prefix that you are using in your partial:

ViewData.TemplateInfo.HtmlFieldPrefix = "checkboxlist";

and the view model collection property: Model.BusinessSubCategories. So make sure you fix the prefix to use the correct property name if you want the default model binder to be able to populate this property when you post back.