Remove HTML helpers with `IDictionary<string, object>` parameters

- see line 2 of #874
- focus on `TextBox[For]()` and `ValidationSummary()`

related fixes included here:
- `TextArea[For]()` documentation incorrectly indicated their `htmlAttributes` parameters were dictionaries
- handle `htmlAttributes` parameters more consistently; create a dictionary only when necessary

src/Microsoft.AspNet.Mvc.Core/Rendering/Html/HtmlHelper.cs

@@ -115,7 +115,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
             object htmlAttributes)
         {
             var url = _urlHelper.Action(actionName, controllerName, routeValues);
-            return GenerateLink(linkText, url, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes));
+            return GenerateLink(linkText, url, GetHtmlAttributeDictionaryOrNull(htmlAttributes));
         }
 
         /// <summary>
@@ -186,13 +186,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
         public MvcForm BeginForm(string actionName, string controllerName, object routeValues, FormMethod method,
                                  object htmlAttributes)
         {
-            // Only need a dictionary if htmlAttributes is non-null. TagBuilder.MergeAttributes() is fine with null.
+            var htmlAttributeDictionary = GetHtmlAttributeDictionaryOrNull(htmlAttributes);
-            IDictionary<string, object> htmlAttributeDictionary = null;
-            if (htmlAttributes != null)
-            {
-                htmlAttributeDictionary = HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes);
-            }
-
             return GenerateForm(actionName, controllerName, routeValues, method, htmlAttributeDictionary);
         }
 
@@ -427,7 +421,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
             object htmlAttributes)
         {
             var url = _urlHelper.RouteUrl(routeName, routeValues, protocol, hostName, fragment);
-            return GenerateLink(linkText, url, HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes));
+            return GenerateLink(linkText, url, GetHtmlAttributeDictionaryOrNull(htmlAttributes));
         }
 
         /// <inheritdoc />
@@ -437,12 +431,17 @@ namespace Microsoft.AspNet.Mvc.Rendering
         }
 
         /// <inheritdoc />
-        public HtmlString ValidationSummary(bool excludePropertyErrors,
+        public HtmlString ValidationSummary(
+            bool excludePropertyErrors,
             string message,
-            IDictionary<string, object> htmlAttributes,
+            object htmlAttributes,
             string tag)
         {
-            return GenerateValidationSummary(excludePropertyErrors, message, htmlAttributes, tag);
+            return GenerateValidationSummary(
+                excludePropertyErrors,
+                message,
+                GetHtmlAttributeDictionaryOrNull(htmlAttributes),
+                tag);
         }
 
         /// <summary>
@@ -476,7 +475,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
         }
 
         /// <inheritdoc />
-        public HtmlString TextBox(string name, object value, string format, IDictionary<string, object> htmlAttributes)
+        public HtmlString TextBox(string name, object value, string format, object htmlAttributes)
         {
             return GenerateTextBox(metadata: null, name: name, value: value, format: format,
                 htmlAttributes: htmlAttributes);
@@ -563,17 +562,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
                 }
             }
 
-            // Only need a dictionary if htmlAttributes is non-null. TagBuilder.MergeAttributes() is fine with null.
+            var htmlAttributeDictionary = GetHtmlAttributeDictionaryOrNull(htmlAttributes);
-            IDictionary<string, object> htmlAttributeDictionary = null;
-            if (htmlAttributes != null)
-            {
-                htmlAttributeDictionary = htmlAttributes as IDictionary<string, object>;
-                if (htmlAttributeDictionary == null)
-                {
-                    htmlAttributeDictionary = AnonymousObjectToHtmlAttributes(htmlAttributes);
-                }
-            }
-
             var explicitValue = isChecked.HasValue;
             if (explicitValue && htmlAttributeDictionary != null)
             {
@@ -691,17 +680,6 @@ namespace Microsoft.AspNet.Mvc.Rendering
             bool useViewData,
             object htmlAttributes)
         {
-            // Only need a dictionary if htmlAttributes is non-null. TagBuilder.MergeAttributes() is fine with null.
-            IDictionary<string, object> htmlAttributeDictionary = null;
-            if (htmlAttributes != null)
-            {
-                htmlAttributeDictionary = htmlAttributes as IDictionary<string, object>;
-                if (htmlAttributeDictionary == null)
-                {
-                    htmlAttributeDictionary = AnonymousObjectToHtmlAttributes(htmlAttributes);
-                }
-            }
-
             // Special-case opaque values and arbitrary binary data.
             var byteArrayValue = value as byte[];
             if (byteArrayValue != null)
@@ -709,6 +687,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
                 value = Convert.ToBase64String(byteArrayValue);
             }
 
+            var htmlAttributeDictionary = GetHtmlAttributeDictionaryOrNull(htmlAttributes);
             return GenerateInput(InputType.Hidden,
                 metadata,
                 name,
@@ -750,7 +729,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
                                         ViewData.TemplateInfo.GetFullHtmlFieldName(htmlFieldName),
                                         IdAttributeDotReplacement));
             tag.SetInnerText(resolvedLabelText);
-            tag.MergeAttributes(AnonymousObjectToHtmlAttributes(htmlAttributes), replaceExisting: true);
+            tag.MergeAttributes(GetHtmlAttributeDictionaryOrNull(htmlAttributes), replaceExisting: true);
             return tag.ToHtmlString(TagRenderMode.Normal);
         }
 
@@ -794,17 +773,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
         protected virtual HtmlString GeneratePassword(ModelMetadata metadata, string name, object value,
             object htmlAttributes)
         {
-            // Only need a dictionary if htmlAttributes is non-null. TagBuilder.MergeAttributes() is fine with null.
+            var htmlAttributeDictionary = GetHtmlAttributeDictionaryOrNull(htmlAttributes);
-            IDictionary<string, object> htmlAttributeDictionary = null;
-            if (htmlAttributes != null)
-            {
-                htmlAttributeDictionary = htmlAttributes as IDictionary<string, object>;
-                if (htmlAttributeDictionary == null)
-                {
-                    htmlAttributeDictionary = AnonymousObjectToHtmlAttributes(htmlAttributes);
-                }
-            }
-
             return GenerateInput(InputType.Password,
                 metadata,
                 name,
@@ -820,17 +789,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
         protected virtual HtmlString GenerateRadioButton(ModelMetadata metadata, string name, object value,
             bool? isChecked, object htmlAttributes)
         {
-            // Only need a dictionary if htmlAttributes is non-null. TagBuilder.MergeAttributes() is fine with null.
+            var htmlAttributeDictionary = GetHtmlAttributeDictionaryOrNull(htmlAttributes);
-            IDictionary<string, object> htmlAttributeDictionary = null;
-            if (htmlAttributes != null)
-            {
-                htmlAttributeDictionary = htmlAttributes as IDictionary<string, object>;
-                if (htmlAttributeDictionary == null)
-                {
-                    htmlAttributeDictionary = AnonymousObjectToHtmlAttributes(htmlAttributes);
-                }
-            }
-
             if (metadata == null)
             {
                 // RadioButton() case. Do not override checked attribute if isChecked is implicit.
@@ -941,7 +900,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
             {
                 InnerHtml = listItemBuilder.ToString()
             };
-            tagBuilder.MergeAttributes(AnonymousObjectToHtmlAttributes(htmlAttributes));
+            tagBuilder.MergeAttributes(GetHtmlAttributeDictionaryOrNull(htmlAttributes));
             tagBuilder.MergeAttribute("name", fullName, true /* replaceExisting */);
             tagBuilder.GenerateId(fullName, IdAttributeDotReplacement);
             if (allowMultiple)
@@ -998,7 +957,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
 
             var tagBuilder = new TagBuilder("textarea");
             tagBuilder.GenerateId(fullName, IdAttributeDotReplacement);
-            tagBuilder.MergeAttributes(AnonymousObjectToHtmlAttributes(htmlAttributes), true);
+            tagBuilder.MergeAttributes(GetHtmlAttributeDictionaryOrNull(htmlAttributes), true);
             if (rows > 0)
             {
                 tagBuilder.MergeAttribute("rows", rows.ToString(CultureInfo.InvariantCulture), true);
@@ -1026,8 +985,9 @@ namespace Microsoft.AspNet.Mvc.Rendering
         }
 
         protected virtual HtmlString GenerateTextBox(ModelMetadata metadata, string name, object value, string format,
-            IDictionary<string, object> htmlAttributes)
+            object htmlAttributes)
         {
+            var htmlAttributeDictionary = GetHtmlAttributeDictionaryOrNull(htmlAttributes);
             return GenerateInput(InputType.Text,
                 metadata,
                 name,
@@ -1037,7 +997,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
                 setId: true,
                 isExplicitValue: true,
                 format: format,
-                htmlAttributes: htmlAttributes);
+                htmlAttributes: htmlAttributeDictionary);
         }
 
         protected virtual HtmlString GenerateInput(InputType inputType, ModelMetadata metadata, string name,
@@ -1189,7 +1149,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
                 tag = ViewContext.ValidationMessageElement;
             }
             var builder = new TagBuilder(tag);
-            builder.MergeAttributes(AnonymousObjectToHtmlAttributes(htmlAttributes));
+            builder.MergeAttributes(GetHtmlAttributeDictionaryOrNull(htmlAttributes));
 
             // Only the style of the span is changed according to the errors if message is null or empty.
             // Otherwise the content and style is handled by the client-side validation.
@@ -1349,6 +1309,22 @@ namespace Microsoft.AspNet.Mvc.Rendering
                     new ClientModelValidationContext(metadata, MetadataProvider)));
         }
 
+        // Only need a dictionary if htmlAttributes is non-null. TagBuilder.MergeAttributes() is fine with null.
+        private static IDictionary<string, object> GetHtmlAttributeDictionaryOrNull(object htmlAttributes)
+        {
+            IDictionary<string, object> htmlAttributeDictionary = null;
+            if (htmlAttributes != null)
+            {
+                htmlAttributeDictionary = htmlAttributes as IDictionary<string, object>;
+                if (htmlAttributeDictionary == null)
+                {
+                    htmlAttributeDictionary = AnonymousObjectToHtmlAttributes(htmlAttributes);
+                }
+            }
+
+            return htmlAttributeDictionary;
+        }
+
         private static string GetInputTypeString(InputType inputType)
         {
             switch (inputType)

src/Microsoft.AspNet.Mvc.Core/Rendering/Html/HtmlHelperOfT.cs

@@ -206,7 +206,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
 
         /// <inheritdoc />
         public HtmlString TextBoxFor<TProperty>([NotNull] Expression<Func<TModel, TProperty>> expression,
-            string format, IDictionary<string, object> htmlAttributes)
+            string format, object htmlAttributes)
         {
             var metadata = GetModelMetadata(expression);
             return GenerateTextBox(metadata, GetExpressionName(expression), metadata.Model, format, htmlAttributes);

src/Microsoft.AspNet.Mvc.Core/Rendering/HtmlHelperInputExtensions.cs

@@ -144,17 +144,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
             string format,
             object htmlAttributes)
         {
-            return htmlHelper.TextBox(name, value, format,
+            return htmlHelper.TextBox(name, value, format, htmlAttributes);
-                HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes));
-        }
-
-        public static HtmlString TextBox(
-            [NotNull] this IHtmlHelper htmlHelper,
-            string name,
-            object value,
-            IDictionary<string, object> htmlAttributes)
-        {
-            return htmlHelper.TextBox(name, value, format: null, htmlAttributes: htmlAttributes);
         }
 
         public static HtmlString TextBoxFor<TModel, TProperty>([NotNull] this IHtmlHelper<TModel> htmlHelper,
@@ -178,14 +168,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
         public static HtmlString TextBoxFor<TModel, TProperty>([NotNull] this IHtmlHelper<TModel> htmlHelper,
             [NotNull] Expression<Func<TModel, TProperty>> expression, string format, object htmlAttributes)
         {
-            return htmlHelper.TextBoxFor(expression, format: format,
+            return htmlHelper.TextBoxFor(expression, format: format, htmlAttributes: htmlAttributes);
-                htmlAttributes: HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes));
-        }
-
-        public static HtmlString TextBoxFor<TModel, TProperty>([NotNull] this IHtmlHelper<TModel> htmlHelper,
-            [NotNull] Expression<Func<TModel, TProperty>> expression, IDictionary<string, object> htmlAttributes)
-        {
-            return htmlHelper.TextBoxFor(expression, format: null, htmlAttributes: htmlAttributes);
         }
 
         public static HtmlString TextArea([NotNull] this IHtmlHelper htmlHelper,

src/Microsoft.AspNet.Mvc.Core/Rendering/HtmlHelperValidationExtensions.cs

@@ -138,10 +138,8 @@ namespace Microsoft.AspNet.Mvc.Rendering
             string message,
             object htmlAttributes)
         {
-            return htmlHelper.ValidationSummary(excludePropertyErrors: false,
+            return htmlHelper.ValidationSummary(
-                message: message,
+                excludePropertyErrors: false, message: message, htmlAttributes: htmlAttributes, tag: null);
-                htmlAttributes: HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes),
-                tag: null);
         }
 
         public static HtmlString ValidationSummary([NotNull] this IHtmlHelper htmlHelper,
@@ -149,10 +147,8 @@ namespace Microsoft.AspNet.Mvc.Rendering
             object htmlAttributes,
             string tag)
         {
-            return htmlHelper.ValidationSummary(excludePropertyErrors: false,
+            return htmlHelper.ValidationSummary(
-                message: message,
+                excludePropertyErrors: false, message: message, htmlAttributes: htmlAttributes, tag: tag);
-                htmlAttributes: HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes),
-                tag: tag);
         }
 
         public static HtmlString ValidationSummary([NotNull] this IHtmlHelper htmlHelper,
@@ -171,10 +167,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
             string message,
             object htmlAttributes)
         {
-            return htmlHelper.ValidationSummary(excludePropertyErrors,
+            return htmlHelper.ValidationSummary(excludePropertyErrors, message, htmlAttributes, tag: null);
-                message,
-                HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes),
-                tag: null);
         }
 
         public static HtmlString ValidationSummary([NotNull] this IHtmlHelper htmlHelper,
@@ -183,31 +176,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
             object htmlAttributes,
             string tag)
         {
-            return htmlHelper.ValidationSummary(excludePropertyErrors,
+            return htmlHelper.ValidationSummary(excludePropertyErrors, message, htmlAttributes, tag);
-                message,
-                HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes),
-                tag);
-        }
-
-        public static HtmlString ValidationSummary([NotNull] this IHtmlHelper htmlHelper,
-            string message,
-            IDictionary<string, object> htmlAttributes)
-        {
-            return htmlHelper.ValidationSummary(excludePropertyErrors: false,
-                message: message,
-                htmlAttributes: htmlAttributes,
-                tag: null);
-        }
-
-        public static HtmlString ValidationSummary([NotNull] this IHtmlHelper htmlHelper,
-            string message,
-            IDictionary<string, object> htmlAttributes,
-            string tag)
-        {
-            return htmlHelper.ValidationSummary(excludePropertyErrors: false,
-                message: message,
-                htmlAttributes: htmlAttributes,
-                tag: tag);
         }
     }
 }

src/Microsoft.AspNet.Mvc.Core/Rendering/IHtmlHelper.cs

@@ -414,8 +414,8 @@ namespace Microsoft.AspNet.Mvc.Rendering
         /// </param>
         /// <param name="rows">Number of rows in the textarea.</param>
         /// <param name="columns">Number of columns in the textarea.</param>
-        /// <param name="htmlAttributes">
+        /// <param name="htmlAttributes">An object that contains the HTML attributes to set for the element.
-        /// <see cref="IDictionary{string, object}"/> containing additional HTML attributes.
+        /// Alternatively, an <see cref="IDictionary{string, object}"/> instance containing the HTML attributes.
         /// </param>
         /// <returns>New <see cref="HtmlString"/> containing the rendered HTML.</returns>
         HtmlString TextArea(string name, string value, int rows, int columns, object htmlAttributes);
@@ -431,11 +431,11 @@ namespace Microsoft.AspNet.Mvc.Rendering
         /// If non-<c>null</c>, value to include in the element. Ignore if named value is found in submitted data.
         /// </param>
         /// <param name="format"></param>
-        /// <param name="htmlAttributes">
+        /// <param name="htmlAttributes">An object that contains the HTML attributes to set for the element.
-        /// <see cref="IDictionary{string, object}"/> containing additional HTML attributes.
+        /// Alternatively, an <see cref="IDictionary{string, object}"/> instance containing the HTML attributes.
         /// </param>
         /// <returns>New <see cref="HtmlString"/> containing the rendered HTML.</returns>
-        HtmlString TextBox(string name, object value, string format, IDictionary<string, object> htmlAttributes);
+        HtmlString TextBox(string name, object value, string format, object htmlAttributes);
 
         /// <summary>
         /// Returns the validation message if an error exists in the <see cref="ModelStateDictionary"/> object.
@@ -458,7 +458,9 @@ namespace Microsoft.AspNet.Mvc.Rendering
         /// <param name="excludePropertyErrors">true to have the summary display model-level errors only, or false to
         /// have the summary display all errors.</param>
         /// <param name="message">The message to display with the validation summary.</param>
-        /// <param name="htmlAttributes">A dictionary that contains the HTML attributes for the element.</param>
+        /// <param name="htmlAttributes">An object that contains the HTML attributes to set for the element.
+        /// Alternatively, an <see cref="IDictionary{string, object}"/> instance containing the HTML attributes.
+        /// </param>
         /// <param name="tag">The tag to wrap the <paramref name="message"/> in the generated HTML.
         /// Its default value is <see cref="ViewContext.ValidationMessageElement" />.</param>
         /// <returns>An <see cref="HtmlString"/> that contains an unordered list (ul element) of validation messages.
@@ -466,7 +468,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
         HtmlString ValidationSummary(
             bool excludePropertyErrors,
             string message,
-            IDictionary<string, object> htmlAttributes,
+            object htmlAttributes,
             string tag);
 
         /// <summary>

src/Microsoft.AspNet.Mvc.Core/Rendering/IHtmlHelperOfT.cs

@@ -223,8 +223,8 @@ namespace Microsoft.AspNet.Mvc.Rendering
         /// <param name="expression">An expression, relative to the current model.</param>
         /// <param name="rows">Number of rows in the textarea.</param>
         /// <param name="columns">Number of columns in the textarea.</param>
-        /// <param name="htmlAttributes">
+        /// <param name="htmlAttributes">An object that contains the HTML attributes to set for the element.
-        /// <see cref="IDictionary{string, object}"/> containing additional HTML attributes.
+        /// Alternatively, an <see cref="IDictionary{string, object}"/> instance containing the HTML attributes.
         /// </param>
         /// <returns>New <see cref="HtmlString"/> containing the rendered HTML.</returns>
         HtmlString TextAreaFor<TProperty>([NotNull] Expression<Func<TModel, TProperty>> expression,
@@ -237,12 +237,12 @@ namespace Microsoft.AspNet.Mvc.Rendering
         /// An expression that identifies the object that contains the properties to render.
         /// </param>
         /// <param name="format"></param>
-        /// <param name="htmlAttributes">
+        /// <param name="htmlAttributes">An object that contains the HTML attributes to set for the element.
-        /// <see cref="IDictionary{string, object}"/> containing additional HTML attributes.
+        /// Alternatively, an <see cref="IDictionary{string, object}"/> instance containing the HTML attributes.
         /// </param>
         /// <returns>New <see cref="HtmlString"/> containing the rendered HTML.</returns>
         HtmlString TextBoxFor<TProperty>([NotNull] Expression<Func<TModel, TProperty>> expression, string format,
-            IDictionary<string, object> htmlAttributes);
+            object htmlAttributes);
 
         /// <summary>
         /// Returns the validation message for the specified expression