Making the HtmlHelper.GetEnumSelectList take DisplayAttribute.GroupNa…

…me into account to create select groups.

samples/MvcSample.Web/Models/TestEnum.cs

@@ -0,0 +1,21 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using System.Linq;
+using System.Threading.Tasks;
+
+namespace MvcSample.Web.Models
+{
+    public enum TestEnum
+    {
+        Zero = 0,
+        [Display(GroupName = "Primes")]
+        One = 1,
+        [Display(GroupName = "Evens", Name = "Dos")]
+        Two = 2,
+        [Display(GroupName = "Primes")]
+        Three = 3,
+        [Display(Name = "4th")]
+        Four = 4
+    }
+}

samples/MvcSample.Web/Models/User.cs

@@ -29,6 +29,7 @@ public User()
         public string About { get; set; }
         public string Log { get; set; }
         public IEnumerable<string> OwnedAddresses { get; private set; }
+        public TestEnum EnumInformation { get; set; }
 
         // This does not bind correctly. Only gets highest value.
         public List<int> ParentsAges { get; private set; }

samples/MvcSample.Web/Views/Home/Create.cshtml

@@ -105,12 +105,22 @@
                         @Html.ListBoxFor(model => model.ParentsAges, (IEnumerable<SelectListItem>)ViewBag.Ages, htmlAttributes: new { @class = "form-control" })
                     </td>
                 </tr>
+                <tr>
+                    <td>
+                        <label class="control-label col-md-2" for="Name">Model.EnumInformation</label>
+                    </td>
+                    <td>
+                        @Html.DropDownList("EnumInformation", Html.GetEnumSelectList<TestEnum>())
+                    </td>
+                    <td></td>
+                </tr>
                 <tr>
                     <td>
                         <input type="submit" value="Save" class="btn btn-default" style="margin-left: 10px" />
                     </td>
                     <td></td>
                 </tr>
+
             </table>
         }
     </div>

src/Microsoft.AspNet.Mvc.Abstractions/ModelBinding/EnumGroupAndName.cs

@@ -0,0 +1,44 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+
+namespace Microsoft.AspNet.Mvc.ModelBinding
+{
+    /// <summary>
+    /// An abstraction used when grouping enum values for <see cref="ModelMetadata.EnumGroupedDisplayNamesAndValues"/>.
+    /// </summary>
+    public struct EnumGroupAndName
+    {
+        /// <summary>
+        /// Initializes a new instance of the EnumGroupAndName structure.
+        /// </summary>
+        /// <param name="group">The group name.</param>
+        /// <param name="name">The name.</param>
+        public EnumGroupAndName(string group, string name)
+        {
+            if (group == null)
+            {
+                throw new ArgumentNullException(nameof(group));
+            }
+
+            if (name == null)
+            {
+                throw new ArgumentNullException(nameof(name));
+            }
+
+            Group = group;
+            Name = name;
+        }
+
+        /// <summary>
+        /// Gets the Group name.
+        /// </summary>
+        public string Group { get; }
+
+        /// <summary>
+        /// Gets the name.
+        /// </summary>
+        public string Name { get; }
+    }
+}

src/Microsoft.AspNet.Mvc.Abstractions/ModelBinding/ModelMetadata.cs

@@ -139,14 +139,14 @@ public string PropertyName
         public abstract ModelMetadata ElementMetadata { get; }
 
         /// <summary>
-        /// Gets the ordered display names and values of all <see cref="Enum"/> values in
+        /// Gets the ordered and grouped display names and values of all <see cref="Enum"/> values in
         /// <see cref="UnderlyingOrModelType"/>.
         /// </summary>
         /// <value>
-        /// An <see cref="IEnumerable{KeyValuePair{string, string}}"/> of mappings between <see cref="Enum"/> field names
-        /// and values. <c>null</c> if <see cref="IsEnum"/> is <c>false</c>.
+        /// An <see cref="IEnumerable{KeyValuePair{EnumGroupAndName, string}"/> of mappings between
+        /// <see cref="Enum"/> field groups, names and values. <c>null</c> if <see cref="IsEnum"/> is <c>false</c>.
         /// </value>
-        public abstract IEnumerable<KeyValuePair<string, string>> EnumDisplayNamesAndValues { get; }
+        public abstract IEnumerable<KeyValuePair<EnumGroupAndName, string>> EnumGroupedDisplayNamesAndValues { get; }
 
         /// <summary>
         /// Gets the names and values of all <see cref="Enum"/> values in <see cref="UnderlyingOrModelType"/>.

src/Microsoft.AspNet.Mvc.Core/ModelBinding/Metadata/DefaultModelMetadata.cs

@@ -272,11 +272,11 @@ public override ModelMetadata ElementMetadata
         }
 
         /// <inheritdoc />
-        public override IEnumerable<KeyValuePair<string, string>> EnumDisplayNamesAndValues
+        public override IEnumerable<KeyValuePair<EnumGroupAndName, string>> EnumGroupedDisplayNamesAndValues
         {
             get
             {
-                return DisplayMetadata.EnumDisplayNamesAndValues;
+                return DisplayMetadata.EnumGroupedDisplayNamesAndValues;
             }
         }
 

src/Microsoft.AspNet.Mvc.Core/ModelBinding/Metadata/DisplayMetadata.cs

@@ -57,11 +57,11 @@ public class DisplayMetadata
         public string EditFormatString { get; set; }
 
         /// <summary>
-        /// Gets the ordered display names and values of all <see cref="System.Enum"/> values in
+        /// Gets the ordered and grouped display names and values of all <see cref="System.Enum"/> values in
         /// <see cref="ModelMetadata.UnderlyingOrModelType"/>. See
-        /// <see cref="ModelMetadata.EnumDisplayNamesAndValues"/>.
+        /// <see cref="ModelMetadata.EnumGroupedDisplayNamesAndValues"/>.
         /// </summary>
-        public IEnumerable<KeyValuePair<string, string>> EnumDisplayNamesAndValues { get; set; }
+        public IEnumerable<KeyValuePair<EnumGroupAndName, string>> EnumGroupedDisplayNamesAndValues { get; set; }
 
         /// <summary>
         /// Gets the names and values of all <see cref="System.Enum"/> values in

src/Microsoft.AspNet.Mvc.DataAnnotations/DataAnnotationsMetadataProvider.cs

@@ -120,19 +120,20 @@ public void GetDisplayMetadata(DisplayMetadataProviderContext context)
                 // Order EnumDisplayNamesAndValues to match Enum.GetNames(). That method orders by absolute value,
                 // then its behavior is undefined (but hopefully stable). Add to EnumNamesAndValues in same order but
                 // Dictionary does not guarantee order will be preserved.
-                var displayNamesAndValues = new List<KeyValuePair<string, string>>();
+                var groupedDisplayNamesAndValues = new List<KeyValuePair<EnumGroupAndName, string>>();
                 var namesAndValues = new Dictionary<string, string>();
                 foreach (var name in Enum.GetNames(underlyingType))
                 {
                     var field = underlyingType.GetField(name);
                     var displayName = GetDisplayName(field);
+                    var groupName = GetDisplayGroup(field);
                     var value = ((Enum)field.GetValue(obj: null)).ToString("d");
 
-                    displayNamesAndValues.Add(new KeyValuePair<string, string>(displayName, value));
+                    groupedDisplayNamesAndValues.Add(new KeyValuePair<EnumGroupAndName, string>(new EnumGroupAndName(groupName, displayName), value));
                     namesAndValues.Add(name, value);
                 }
 
-                displayMetadata.EnumDisplayNamesAndValues = displayNamesAndValues;
+                displayMetadata.EnumGroupedDisplayNamesAndValues = groupedDisplayNamesAndValues;
                 displayMetadata.EnumNamesAndValues = namesAndValues;
             }
 
@@ -258,5 +259,22 @@ private static string GetDisplayName(FieldInfo field)
 
             return field.Name;
         }
+
+        // Return non-empty group specified in a [Display] attribute for a field, if any; string.Empty otherwise.
+        private static string GetDisplayGroup(FieldInfo field)
+        {
+            var display = field.GetCustomAttribute<DisplayAttribute>(inherit: false);
+            if (display != null)
+            {
+                // Note [Display(Group = "")] is allowed.
+                var group = display.GetGroupName();
+                if (group != null)
+                {
+                    return group;
+                }
+            }
+
+            return string.Empty;
+        }
     }
 }

src/Microsoft.AspNet.Mvc.ViewFeatures/ViewFeatures/HtmlHelper.cs

@@ -1168,14 +1168,25 @@ protected virtual IEnumerable<SelectListItem> GetEnumSelectList(ModelMetadata me
             }
 
             var selectList = new List<SelectListItem>();
-            foreach (var keyValuePair in metadata.EnumDisplayNamesAndValues)
+            var groupList = new Dictionary<string, SelectListGroup>();
+            foreach (var keyValuePair in metadata.EnumGroupedDisplayNamesAndValues)
             {
                 var selectListItem = new SelectListItem
                 {
-                    Text = keyValuePair.Key,
+                    Text = keyValuePair.Key.Name,
                     Value = keyValuePair.Value,
                 };
 
+                if (!string.IsNullOrEmpty(keyValuePair.Key.Group))
+                {
+                    if (!groupList.ContainsKey(keyValuePair.Key.Group))
+                    {
+                        groupList[keyValuePair.Key.Group] = new SelectListGroup() { Name = keyValuePair.Key.Group };
+                    }
+
+                    selectListItem.Group = groupList[keyValuePair.Key.Group];
+                }
+
                 selectList.Add(selectListItem);
             }
 

test/Microsoft.AspNet.Mvc.Abstractions.Test/ModelBinding/ModelMetadataTest.cs

@@ -369,7 +369,7 @@ public override ModelMetadata ElementMetadata
                 }
             }
 
-            public override IEnumerable<KeyValuePair<string, string>> EnumDisplayNamesAndValues
+            public override IEnumerable<KeyValuePair<EnumGroupAndName, string>> EnumGroupedDisplayNamesAndValues
             {
                 get
                 {

test/Microsoft.AspNet.Mvc.Core.Test/ModelBinding/Metadata/DefaultModelMetadataTest.cs

@@ -57,7 +57,7 @@ public void DefaultValues()
             Assert.Null(metadata.DisplayName);
             Assert.Null(metadata.EditFormatString);
             Assert.Null(metadata.ElementMetadata);
-            Assert.Null(metadata.EnumDisplayNamesAndValues);
+            Assert.Null(metadata.EnumGroupedDisplayNamesAndValues);
             Assert.Null(metadata.EnumNamesAndValues);
             Assert.Null(metadata.NullDisplayText);
             Assert.Null(metadata.TemplateHint);