Correcting checkbox element such that it maintains postback state.

This fixes the issue where a checkbox would lose its checked state after posting back and a model validation occurs.

src/Orchard.Web/Modules/Orchard.DynamicForms/Elements/FormElement.cs

@@ -26,11 +26,19 @@ namespace Orchard.DynamicForms.Elements {
             get { return State.Get("Value"); }
         }
 
+        /// <summary>
+        /// The runtime value for this element. This is either the default value, or the submitted value.
+        /// </summary>
         public string RuntimeValue {
             get { return _runtimeValue.Value; }
             set { _runtimeValue = new Lazy<string>(() => value); }
         }
 
+        /// <summary>
+        /// The value posted back for this element.
+        /// </summary>
+        public string PostedValue { get; set; }
+
         public string FormBindingContentType {
             get { return State.Get("FormBindingContentType"); }
             set { State["FormBindingContentType"] = value; }

src/Orchard.Web/Modules/Orchard.DynamicForms/Handlers/ReadFormValuesHandler.cs

@@ -22,6 +22,7 @@ namespace Orchard.DynamicForms.Handlers {
             var combinedValues = String.Join(",", items);
             context.Output[key] = combinedValues;
             element.RuntimeValue = combinedValues;
+            element.PostedValue = combinedValues;
         }
     }
 }

src/Orchard.Web/Modules/Orchard.DynamicForms/Views/Element-Form-Checkbox.cshtml

@@ -9,6 +9,10 @@
     tagBuilder.Attributes["name"] = element.Name;
     tagBuilder.Attributes["value"] = Model.TokenizedValue;
     tagBuilder.AddClientValidationAttributes((IDictionary<string, string>)Model.ClientValidationAttributes);
+
+    if (!String.IsNullOrWhiteSpace(element.PostedValue)) {
+        tagBuilder.Attributes["checked"] = "checked";
+    }
 }
 @if (element.ShowLabel) {
     <label>