Added HtmlHelper extesions for creating dependent HTMLHelper against …

…sub-property or a random model type (with and without instance)

Partially addresses #95 and #107

ChameleonForms/ChameleonForms.csproj

@@ -91,6 +91,7 @@
     <Compile Include="Enums\TextInputType.cs" />
     <Compile Include="Extensions.cs" />
     <Compile Include="PartialViewForm.cs" />
+    <Compile Include="HtmlHelperExtensions.cs" />
     <Compile Include="PartialViewSection.cs" />
     <Compile Include="ReSharper\ReSharperAnnotations.cs" />
     <Compile Include="Templates\TwitterBootstrap3\ButtonSize.cs" />

ChameleonForms/HtmlHelperExtensions.cs

@@ -0,0 +1,91 @@
+using System;
+using System.Linq.Expressions;
+using System.Web.Mvc;
+using System.Web.Routing;
+
+namespace ChameleonForms
+{
+    /// <summary>
+    /// Extension methods against HtmlHelper.
+    /// </summary>
+    // http://maxtoroq.github.io/2012/07/patterns-for-aspnet-mvc-plugins-viewmodels.html
+    public static class HtmlHelperExtensions
+    {
+        /// <summary>
+        /// Creates a HTML helper from a parent model to use a sub-property as it's model.
+        /// </summary>
+        /// <typeparam name="TParentModel">The model of the parent type</typeparam>
+        /// <typeparam name="TChildModel">The model of the sub-property to use</typeparam>
+        /// <param name="helper">The parent HTML helper</param>
+        /// <param name="propertyFor">The sub-property to use</param>
+        /// <param name="bindFieldsToParent">Whether to set field names to bind to the parent model type (true) or the sub-property type (false)</param>
+        /// <returns>A HTML helper against the sub-property</returns>
+        public static DisposableHtmlHelper<TChildModel> For<TParentModel, TChildModel>(this HtmlHelper<TParentModel> helper,
+            Expression<Func<TParentModel, TChildModel>> propertyFor, bool bindFieldsToParent)
+        {
+            return helper.For(propertyFor.Compile().Invoke(helper.ViewData.Model),
+                bindFieldsToParent ? ExpressionHelper.GetExpressionText(propertyFor) : null);
+        }
+
+        /// <summary>
+        /// Creates a HTML helper based on another HTML helper against a different model type.
+        /// </summary>
+        /// <typeparam name="TModel">The model type to create a helper for</typeparam>
+        /// <param name="htmlHelper">The original HTML helper</param>
+        /// <param name="model">An instance of the model type to use as the model</param>
+        /// <param name="htmlFieldPrefix">A prefix value to use for field names</param>
+        /// <returns>The HTML helper against the other model type</returns>
+        public static DisposableHtmlHelper<TModel> For<TModel>(this HtmlHelper htmlHelper, TModel model = default(TModel), string htmlFieldPrefix = null)
+        {
+            var viewDataContainer = CreateViewDataContainer(htmlHelper.ViewData, model);
+
+            var templateInfo = viewDataContainer.ViewData.TemplateInfo;
+
+            if (!String.IsNullOrEmpty(htmlFieldPrefix))
+                templateInfo.HtmlFieldPrefix = templateInfo.GetFullHtmlFieldName(htmlFieldPrefix);
+
+            var viewContext = htmlHelper.ViewContext;
+            var newViewContext = new ViewContext(viewContext.Controller.ControllerContext, viewContext.View, viewDataContainer.ViewData, viewContext.TempData, viewContext.Writer);
+
+            return new DisposableHtmlHelper<TModel>(newViewContext, viewDataContainer, htmlHelper.RouteCollection);
+        }
+
+        static IViewDataContainer CreateViewDataContainer(ViewDataDictionary viewData, object model)
+        {
+
+            var newViewData = new ViewDataDictionary(viewData)
+            {
+                Model = model
+            };
+
+            newViewData.TemplateInfo = new TemplateInfo
+            {
+                HtmlFieldPrefix = newViewData.TemplateInfo.HtmlFieldPrefix
+            };
+
+            return new ViewDataContainer
+            {
+                ViewData = newViewData
+            };
+        }
+
+        class ViewDataContainer : IViewDataContainer
+        {
+
+            public ViewDataDictionary ViewData { get; set; }
+        }
+    }
+
+    /// <summary>
+    /// HTML helper that can be created in a using block.
+    /// </summary>
+    /// <typeparam name="TModel">The model type of the HTML helper</typeparam>
+    public class DisposableHtmlHelper<TModel> : HtmlHelper<TModel>, IDisposable
+    {
+        /// <inheritdoc />
+        public DisposableHtmlHelper(ViewContext viewContext, IViewDataContainer viewDataContainer) : base(viewContext, viewDataContainer) {}
+        /// <inheritdoc />
+        public DisposableHtmlHelper(ViewContext viewContext, IViewDataContainer viewDataContainer, RouteCollection routeCollection) : base(viewContext, viewDataContainer, routeCollection) {}
+        public void Dispose() {}
+    }
+}