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POMVC 3 CheckboxList and me...Part 3. Try specifying the type arguments explicitly
 

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  1. POMVC 3 CheckboxList and me...Part 3. Try specifying the type arguments explicitly
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    <p>This IS fun.</p> <p>Ok, I have the following <strong>model(s)</strong>:</p> <pre><code>public class My : BusinessCategory { [Display(Name = "What types of energy do you use?")] public List&lt;MyTypes&gt; MyTypeList { get; set; } public bool? FirstOption { get; set; } public bool? SecondOption{ get; set; } public bool? ThirdOption{ get; set; } public bool? FourthOption { get; set; } </code></pre> <p>}</p> <p>Where MyTypes:</p> <pre><code>public class MyTypes { public int MyTypeId { get; set; } public string MyTypeName { get; set; } public bool? MyTypeValue { get; set; } } </code></pre> <p>My controller is as follows:</p> <pre><code>public ActionResult My(Guid id) { try { var model = Model(id); SetMyTypeList(model.My); ViewBag.MyTypeMe = new MultiSelectList(model.My.MyTypeList, "MyTypeValue", "MyTypeName"); return View(model.My); } catch (Exception ex) { ExceptionHelper.WriteLog(ex); return RedirectToAction("Error"); } } private void SetMyTypeList(My model) { model.MyTypeList = new List&lt;MyTypes&gt;(); model.MyTypeList.Add(new MyTypes { MyTypeId = 1, MyTypeName = GetName.GetDisplayName(model, m =&gt; m.FirstOption), MyTypeValue = model.FirstOption }); model.MyTypeList.Add(new MyTypes { MyTypeId = 2, MyTypeName = GetName.GetDisplayName(model, m =&gt; m.SecondOption), MyTypeValue = model.SecondOption}); model.MyTypeList.Add(new MyTypes { MyTypeId = 3, MyTypeName = GetName.GetDisplayName(model, m =&gt; m.ThirdOption), MyTypeValue = model.ThirdOption}); model.MyTypeList.Add(new MyTypes { MyTypeId = 4, MyTypeName = GetName.GetDisplayName(model, m =&gt; m.FourthOption), MyTypeValue = model.FourthOption }); } public static string GetDisplayName&lt;TModel, TProperty&gt;(TModel model, Expression&lt;Func&lt;TModel, TProperty&gt;&gt; expression) { return ModelMetadata.FromLambdaExpression&lt;TModel, TProperty&gt;(expression, new ViewDataDictionary&lt;TModel&gt;(model)).DisplayName; } </code></pre> <p>And finally the view is as follows:</p> <pre><code>@model Valpak.Websites.HealthChecker.Models.My @{ ViewBag.Title = "My"; } &lt;h2&gt; My&lt;/h2&gt; @using (Html.BeginForm()) { @Html.ValidationSummary(true) &lt;fieldset&gt; &lt;legend&gt;My Management&lt;/legend&gt; &lt;div style="text-align: left; padding-left: 47%;"&gt; @Html.ListBoxFor(model =&gt; model.MyTypeList, ViewBag.MyTypeMe as MultiSelectList) @Html.CheckBoxListFor(model =&gt; model.MyTypeList, ViewBag.EnergyTypeMe as MultiSelectList, Model.ReviewId) &lt;/div&gt; &lt;p&gt; &lt;input type="submit" value="Continue" /&gt; &lt;/p&gt; &lt;/fieldset&gt; } &lt;div&gt; @Html.ActionLink("Cancel and return to categories", "BusinessSummary", new { id = Model.ReviewId }) &lt;/div&gt; </code></pre> <p>CheckboxListFor, if it was working, would use the following extension:</p> <pre><code>public static class HtmlHelper { //Extension public static MvcHtmlString CheckBoxListFor&lt;TModel, TProperty&gt;(this HtmlHelper&lt;TModel&gt; htmlHelper, Expression&lt;Func&lt;TModel, TProperty[]&gt;&gt; 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&lt;string&gt; for easy manipulation List&lt;string&gt; selectedValues = new List&lt;string&gt;(); if (list != null) { selectedValues = new List&lt;TProperty&gt;(list).ConvertAll&lt;string&gt;(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("&lt;div&gt;&lt;input type=\"checkbox\" name=\"{0}\" id=\"{0}_{1}\" " + "value=\"{1}\" {2} /&gt;&lt;label for=\"{0}_{1}\"&gt;{3}&lt;/label&gt;&lt;/div&gt;", propertyName, item.Value, selectedValues.Contains(item.Value) ? "checked=\"checked\"" : "", item.Text); } return MvcHtmlString.Create(divTag.ToString()); } } </code></pre> <p>Can someone you explain in very simplistic terms (I’m a bit dense) why I can use the ListBoxFor example but this dies and gives me the following error when I use the checkbox?</p> <pre><code>CS0411: The type arguments for method 'Extensions.HtmlHelper.CheckBoxListFor&lt;TModel,TProperty&gt;(System.Web.Mvc.HtmlHelper&lt;TModel&gt;, System.Linq.Expressions.Expression&lt;System.Func&lt;TModel,TProperty[]&gt;&gt;, System.Web.Mvc.MultiSelectList, System.Guid, object)' cannot be inferred from the usage. Try specifying the type arguments explicitly. </code></pre> <p>Can anyone offer any sort of work around as I’d quite like to use my :’(</p> <p>As always, apologies for my ignorance.</p>
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