Allow the use of the Prompt property of DisplayAttribute for the placeholder attribute of input fields (addresses #3723)

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

@@ -258,6 +258,11 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// <value>The order value of the current metadata.</value>
         public abstract int Order { get; }
 
+        /// <summary>
+        /// Gets the text to display as a placeholder value for an editor.
+        /// </summary>
+        public abstract string Placeholder { get; }
+
         /// <summary>
         /// Gets the text to display when the model is <c>null</c>.
         /// </summary>

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

@@ -432,6 +432,20 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
             }
         }
 
+        /// <inheritdoc />
+        public override string Placeholder
+        {
+            get
+            {
+                if (DisplayMetadata.Placeholder == null)
+                {
+                    return null;
+                }
+
+                return DisplayMetadata.Placeholder();
+            }
+        }
+
         /// <inheritdoc />
         public override ModelPropertyCollection Properties
         {

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

@@ -115,6 +115,12 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
         /// </summary>
         public int Order { get; set; } = 10000;
 
+        /// <summary>
+        /// Gets or sets a delegate which is used to get a value for the
+        /// model's placeholder text. See <see cref="ModelMetadata.Placeholder"/>.
+        /// </summary>
+        public Func<string> Placeholder { get; set; }
+
         /// <summary>
         /// Gets or sets a value indicating whether or not to include in the model value in display.
         /// See <see cref="ModelMetadata.ShowForDisplay"/>

src/Microsoft.AspNetCore.Mvc.DataAnnotations/Internal/DataAnnotationsMetadataProvider.cs

@@ -84,6 +84,7 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             if (displayAttribute != null)
             {
                 displayMetadata.Description = () => displayAttribute.GetDescription();
+                displayMetadata.Placeholder = () => displayAttribute.GetPrompt();
             }
 
             // DisplayFormatString

src/Microsoft.AspNetCore.Mvc.ViewFeatures/ViewFeatures/DefaultHtmlGenerator.cs

@@ -26,6 +26,10 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
         private static readonly MethodInfo ConvertEnumFromStringMethod =
             typeof(DefaultHtmlGenerator).GetTypeInfo().GetDeclaredMethod(nameof(ConvertEnumFromString));
 
+        // See: (http://www.w3.org/TR/html5/forms.html#the-input-element)
+        private static readonly string[] _placeholderInputTypes =
+            new[] { "text", "search", "url", "tel", "email", "password", "number" };
+
         private readonly IAntiforgery _antiforgery;
         private readonly IClientModelValidatorProvider _clientModelValidatorProvider;
         private readonly IModelMetadataProvider _metadataProvider;
@@ -1134,12 +1138,24 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
                     nameof(expression));
             }
 
+            var inputTypeString = GetInputTypeString(inputType);
             var tagBuilder = new TagBuilder("input");
             tagBuilder.TagRenderMode = TagRenderMode.SelfClosing;
             tagBuilder.MergeAttributes(htmlAttributes);
-            tagBuilder.MergeAttribute("type", GetInputTypeString(inputType));
+            tagBuilder.MergeAttribute("type", inputTypeString);
             tagBuilder.MergeAttribute("name", fullName, replaceExisting: true);
 
+            var suppliedTypeString = tagBuilder.Attributes["type"];
+            if (_placeholderInputTypes.Contains(suppliedTypeString))
+            {
+                modelExplorer = modelExplorer ?? ExpressionMetadataProvider.FromStringExpression(expression, viewContext.ViewData, _metadataProvider);
+                var placeholder = modelExplorer.Metadata.Placeholder;
+                if (!string.IsNullOrEmpty(placeholder))
+                {
+                    tagBuilder.MergeAttribute("placeholder", placeholder);
+                }
+            }
+
             var valueParameter = FormatValue(value, format);
             var usedModelState = false;
             switch (inputType)

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

@@ -520,6 +520,14 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
                 }
             }
 
+            public override string Placeholder
+            {
+                get
+                {
+                    throw new NotImplementedException();
+                }
+            }
+
             public override ModelPropertyCollection Properties
             {
                 get

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

@@ -62,6 +62,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
             Assert.Null(metadata.NullDisplayText);
             Assert.Null(metadata.TemplateHint);
             Assert.Null(metadata.SimpleDisplayProperty);
+            Assert.Null(metadata.Placeholder);
 
             Assert.Equal(10000, ModelMetadata.DefaultOrder);
             Assert.Equal(ModelMetadata.DefaultOrder, metadata.Order);

test/Microsoft.AspNetCore.Mvc.DataAnnotations.Test/Internal/DataAnnotationsMetadataProviderTest.cs

@@ -26,6 +26,7 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
                     { new DisplayAttribute() { Description = "d" }, d => d.Description(), "d" },
                     { new DisplayAttribute() { Name = "DN" }, d => d.DisplayName(), "DN" },
                     { new DisplayAttribute() { Order = 3 }, d => d.Order, 3 },
+                    { new DisplayAttribute() { Prompt = "Enter Value" }, d => d.Placeholder(), "Enter Value" },
 
                     { new DisplayColumnAttribute("Property"), d => d.SimpleDisplayProperty, "Property" },
 

test/Microsoft.AspNetCore.Mvc.DataAnnotations.Test/Internal/ModelMetadataProviderTest.cs

@@ -194,6 +194,9 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
                     {
                         new DisplayAttribute { Name = "value" }, metadata => metadata.DisplayName
                     },
+                    {
+                        new DisplayAttribute { Prompt = "value" }, metadata => metadata.Placeholder
+                    },
                     {
                         new DisplayFormatAttribute { DataFormatString = "value" },
                         metadata => metadata.DisplayFormatString
@@ -422,6 +425,22 @@ namespace Microsoft.AspNetCore.Mvc.DataAnnotations.Internal
             Assert.Equal("description", result);
         }
 
+        [Fact]
+        public void DisplayAttribute_PromptAsPlaceholder()
+        {
+            // Arrange
+            var display = new DisplayAttribute() { Prompt = "prompt" };
+            var provider = CreateProvider(new[] { display });
+
+            var metadata = provider.GetMetadataForType(typeof(string));
+
+            // Act
+            var result = metadata.Placeholder;
+
+            // Assert
+            Assert.Equal("prompt", result);
+        }
+
         [Fact]
         public void DisplayName_FromResources_GetsRecomputed()
         {

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/Rendering/HtmlHelperPasswordTest.cs

@@ -399,6 +399,21 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
                 HtmlContentUtilities.HtmlContentToString(passwordResult));
         }
 
+        [Fact]
+        public void PasswordFor_GeneratesPlaceholderAttribute_WhenDisplayAttributePromptIsSet()
+        {
+            // Arrange
+            var expected = @"<input id=""HtmlEncode[[Property7]]"" name=""HtmlEncode[[Property7]]"" placeholder=""HtmlEncode[[placeholder]]"" type=""HtmlEncode[[password]]"" />";
+            var model = new PasswordModel();
+            var helper = DefaultTemplatesUtilities.GetHtmlHelper(model);
+
+            // Act
+            var result = helper.PasswordFor(m => m.Property7, htmlAttributes: null);
+
+            // Assert
+            Assert.Equal(expected, HtmlContentUtilities.HtmlContentToString(result));
+        }
+
         private static ViewDataDictionary<PasswordModel> GetViewDataWithNullModelAndNonEmptyViewData()
         {
             return new ViewDataDictionary<PasswordModel>(new EmptyModelMetadataProvider())
@@ -443,6 +458,9 @@ namespace Microsoft.AspNetCore.Mvc.Rendering
             public Dictionary<string, string> Property3 { get; } = new Dictionary<string, string>();
 
             public NestedClass Property4 { get; } = new NestedClass();
+
+            [Display(Prompt = "placeholder")]
+            public string Property7 { get; set; }
         }
 
         public class NestedClass

test/Microsoft.AspNetCore.Mvc.ViewFeatures.Test/Rendering/HtmlHelperTextBoxTest.cs

@@ -0,0 +1,64 @@
+// 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 Microsoft.AspNetCore.Mvc.TestCommon;
+using System.ComponentModel.DataAnnotations;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Mvc.Rendering
+{
+    public class HtmlHelperTextBoxTest
+    {
+        [Theory]
+        [InlineData("text")]
+        [InlineData("search")]
+        [InlineData("url")]
+        [InlineData("tel")]
+        [InlineData("email")]
+        [InlineData("number")]
+        public void TextBoxFor_GeneratesPlaceholderAttribute_WhenDisplayAttributePromptIsSetAndTypeIsValid(string type)
+        {
+            // Arrange            
+            var model = new TextBoxModel();
+            var helper = DefaultTemplatesUtilities.GetHtmlHelper(model);
+
+            // Act
+            var result = HtmlContentUtilities.HtmlContentToString(helper.TextBoxFor(m => m.Property1, new { type }));
+
+            // Assert
+            Assert.True(result.Contains(@"placeholder=""HtmlEncode[[placeholder]]"""));
+        }
+
+        [Theory]
+        [InlineData("hidden")]
+        [InlineData("date")]
+        [InlineData("time")]
+        [InlineData("range")]
+        [InlineData("color")]
+        [InlineData("checkbox")]
+        [InlineData("radio")]
+        [InlineData("submit")]
+        [InlineData("reset")]
+        [InlineData("button")]
+        [InlineData("image")]
+        [InlineData("file")]
+        public void TextBoxFor_DoesNotGeneratePlaceholderAttribute_WhenDisplayAttributePromptIsSetAndTypeIsInvalid(string type)
+        {
+            // Arrange            
+            var model = new TextBoxModel();
+            var helper = DefaultTemplatesUtilities.GetHtmlHelper(model);
+
+            // Act
+            var result = HtmlContentUtilities.HtmlContentToString(helper.TextBoxFor(m => m.Property1, new { type }));
+
+            // Assert
+            Assert.False(result.Contains(@"placeholder=""HtmlEncode[[placeholder]]"""));
+        }
+
+        private class TextBoxModel
+        {
+            [Display(Prompt = "placeholder")]
+            public string Property1 { get; set; }
+        }
+    }
+}