MVC 4, Checkbox list and me - asp.net-mvc

Question

Morning all.
I can see this has been discussed elsewhere but was wondering if anything had change or things made simpler in MVC 4 for simpletons like me?!
Scenario
I have the following,edited, model:
public class CorporateDetails
{
public Guid? Id { get; set; }
[Key]
public int CorporateDetailId { get; set; }
public int? EmsId { get; set; }
public string EmsName { get; set; }
public virtual EmsType EmsType { get; set; }
}
public class EmsType
{
[Key]
public int? EmsId { get; set; }
public string EmsName { get; set; }
public virtual ICollection<EmsType> EmsTypes { get; set; }
}
With the following standard create view:
<fieldset>
<legend>CorporateDetails</legend>
<div class="editor-label">
#Html.LabelFor(model => model.EmsId, "EmsType")
</div>
<div class="editor-field">
#Html.DropDownList("EmsId", String.Empty)
#Html.ValidationMessageFor(model => model.EmsId)
</div>
<div class="editor-label">
#Html.LabelFor(model => model.EmsName)
</div>
<div class="editor-field">
#Html.EditorFor(model => model.EmsName)
#Html.ValidationMessageFor(model => model.EmsName)
</div>
<p>
<input type="submit" value="Create" />
</p>
</fieldset>
This gives me, out of the box, a beautiful drop down list a la Scott Gu's blog
Now my real question is this - how can I effectively convert this drop down box to what will effectively be a multi select,checkbox list?
Again, apologies for going over trodden ground but I was just testing the water to see if any updates have occurred.
Please note, first MVC project so go gently, I'm feeling very thick again :'(

Answer 1

Right ok, I have got it sorted - hurrah! As you can see from the comments, there were a few issues that came up but please find below the complete solution which DOES work :D
Model
public class CorporateDetails
{
public Guid? Id { get; set; }
[Key]
public int CorporateDetailId { get; set; }
public int[] EmsId { get; set; }
}
public class EmsType
{
[Key]
public int EmsId { get; set; }
public string EmsName { get; set; }
public virtual ICollection<EmsType> EmsTypes { get; set; }
}
Controller
public ActionResult Create()
{
CorporateDetails corporatedetails = new CorporateDetails();
ViewBag.EmsId = new MultiSelectList(db.EmsTypes, "EmsId", "EmsName");
return View(corporatedetails);
}
Extension (placed in a folder in the root of the project)
public static MvcHtmlString CheckBoxListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty[]>> expression, MultiSelectList multiSelectList, object htmlAttributes = null)
{
//Derive property name for checkbox name
MemberExpression body = expression.Body as MemberExpression;
string propertyName = body.Member.Name;
//Get currently select values from the ViewData model
TProperty[] list = expression.Compile().Invoke(htmlHelper.ViewData.Model);
//Convert selected value list to a List<string> for easy manipulation
List<string> selectedValues = new List<string>();
if (list != null)
{
selectedValues = new List<TProperty>(list).ConvertAll<string>(delegate(TProperty i) { return i.ToString(); });
}
//Create div
TagBuilder divTag = new TagBuilder("div");
divTag.MergeAttributes(new RouteValueDictionary(htmlAttributes), true);
//Add checkboxes
foreach (SelectListItem item in multiSelectList)
{
divTag.InnerHtml += String.Format("<div><input type=\"checkbox\" name=\"{0}\" id=\"{0}_{1}\" " +
"value=\"{1}\" {2} /><label for=\"{0}_{1}\">{3}</label></div>",
propertyName,
item.Value,
selectedValues.Contains(item.Value) ? "checked=\"checked\"" : "",
item.Text);
}
return MvcHtmlString.Create(divTag.ToString());
}
Extension registered in web config of the Views
<pages pageBaseType="System.Web.Mvc.WebViewPage">
<namespaces>
<add namespace="System.Web.Mvc" />
<add namespace="System.Web.Mvc.Ajax" />
<add namespace="System.Web.Mvc.Html" />
<add namespace="System.Web.Optimization"/>
<add namespace="System.Web.Routing" />
<add namespace="MyProject.Extensions" />
</namespaces>
</pages>
View
#model Valpak.Websites.HealthChecker.Models.CorporateDetails
#{
ViewBag.Title = "Create";
}
<h2>Create</h2>
#using (Html.BeginForm())
{
#Html.ValidationSummary(true)
<fieldset>
<legend>CorporateDetails</legend>
<div class="editor-label">
#Html.CheckBoxListFor(model => model.EmsId, (MultiSelectList) ViewBag.EmsId)
</div>
<p>
<input type="submit" value="Create" />
</p>
</fieldset>
}
<div>
#Html.ActionLink("Back to List", "Index")
</div>
#section Scripts {
#Scripts.Render("~/bundles/jqueryval")
}
Which gives me a lovely list of check boxes. Hurrah!
Thanks Darin for your help, I've marked this as the answer but +50 for your time and effort.

Answer 2

Nice solution -
Just for others reference - I, like you, had run into a need for a checkboxlist - I have been using this here:
http://www.codeproject.com/Articles/292050/CheckBoxList-For-a-missing-MVC-extension
It works great... very well written - hope this can help someone.
Loren

Answer 3

No changes occurred in ASP.NET MVC 4 RC in this aspect and are unlikely to occur when it hits RTM.
But you could still implement a custom helper to achieve that. And you could even improve this helper so that it takes a lambda expression as first argument instead of a string in order to have strongly typed version.
And if you are not using enums here's another example.

Answer 4

If you pass selected value to MultiSelected (parameter #4)
ViewBag.VfonctionIds = new MultiSelectList(db.tbIntervenantFonctionTypes, "intervenantFonctionType_id", "Nom", fonctionSelected);
Change the Helper to
public static MvcHtmlString CheckBoxListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty[]>> expression, MultiSelectList multiSelectList, object htmlAttributes = null)
{
//Derive property name for checkbox name
MemberExpression body = expression.Body as MemberExpression;
string propertyName = body.Member.Name;
//Create div
TagBuilder divTag = new TagBuilder("div");
divTag.MergeAttributes(new RouteValueDictionary(htmlAttributes), true);
//Add checkboxes
foreach (SelectListItem item in multiSelectList)
{
divTag.InnerHtml += String.Format("<div><input type=\"checkbox\" name=\"{0}\" id=\"{0}_{1}\" " +
"value=\"{1}\" {2} /><label for=\"{0}_{1}\">{3}</label></div>",
propertyName,
item.Value,
(item.Selected) ? "checked=\"checked\"" : "",
item.Text);
}
return MvcHtmlString.Create(divTag.ToString());
}