如何显示 DisplayAttribute. Description 属性值？

我有一个模型类，其属性如下:

[Display(Name = "Phone", Description="Hello World!")]
public string Phone1 { get; set; }

在我的视图中显示标签和呈现输入文本框非常简单:

@Html.LabelFor(model => model.Organization.Phone1)
@Html.EditorFor(model => model.Organization.Phone1)
@Html.ValidationMessageFor(model => model.Organization.Phone1)

但是如何呈现 Description 注释属性的值，即“ Hello World!”？

51652 次浏览
小开

您必须编写一个自定义助手，它将反映您的模型，以给予 Description 属性值。

小开 
var attrib = (DisplayAttribute)Attribute.GetCustomAttribute(
member, typeof(DisplayAttribute));
var desc = attrib == null ? "" : attrib.GetDescription()
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最佳答案

我最后得到了这样一个帮手:

using System;
using System.Linq.Expressions;
using System.Web.Mvc;


public static class MvcHtmlHelpers
{
public static MvcHtmlString DescriptionFor<TModel, TValue>(this HtmlHelper<TModel> self, Expression<Func<TModel, TValue>> expression)
{
var metadata = ModelMetadata.FromLambdaExpression(expression, self.ViewData);
var description = metadata.Description;


return MvcHtmlString.Create(string.Format(@"<span>{0}</span>", description));
}
}

感谢那些引导我走向正确方向的人:)

小开

使用本文中关于如何使用 显示窗体中字段的可视提示的技术，您可以通过以下方式访问该值:

@Html.TextBoxFor(
model => model.Email ,
new { title = ModelMetadata.FromLambdaExpression<RegisterModel , string>(
model => model.Email , ViewData ).Description } )
小开

我本来打算使用 接受的答案，但是它不适用于 ASP.NET Core 1/2(也就是 MVC 6) ，因为 ModelMetadata.FromLambdaExpression已经不存在了，而且已经被移到了 ExpressionMetadataProvider(使用方式也略有改变)。

这是一个更新后的扩展方法，你可以在 ASP.NET Core 1.1 & 2中使用:

using System;
using System.Linq.Expressions;
using Microsoft.AspNetCore.Html;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures.Internal;


public static class HtmlExtensions
{
public static IHtmlContent DescriptionFor<TModel, TValue>(this IHtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression)
{
if (html == null) throw new ArgumentNullException(nameof(html));
if (expression == null) throw new ArgumentNullException(nameof(expression));


var modelExplorer = ExpressionMetadataProvider.FromLambdaExpression(expression, html.ViewData, html.MetadataProvider);
if (modelExplorer == null) throw new InvalidOperationException($"Failed to get model explorer for {ExpressionHelper.GetExpressionText(expression)}");


return new HtmlString(modelExplorer.Metadata.Description);
}
}

ASP.NET Core 1

对于 ASP.NET Core 1，同样的代码可以工作，但是需要不同的名称空间 usings:

using System;
using System.Linq.Expressions;
using Microsoft.AspNet.Html.Abstractions;
using Microsoft.AspNet.Mvc.ViewFeatures;

用法

@Html.DescriptionFor(model => model.Phone1)
小开

除了雅各布•盖德(Jakob Gade)的一个很棒的回答:

如果您需要支持 DescriptionAttribute而不是 DisplayAttribute，那么如果我们覆盖 MetadataProvider，他伟大的解决方案仍然可以工作:

public class ExtendedModelMetadataProvider : DataAnnotationsModelMetadataProvider
{
protected override ModelMetadata CreateMetadata(IEnumerable<System.Attribute> attributes, Type containerType, Func<object> modelAccessor, Type modelType, string propertyName)
{
//Possible Multiple Enumerations on IEnumerable fix
var attributeList = attributes as IList<System.Attribute> ?? attributes.ToList();


//Default behavior
var data = base.CreateMetadata(attributeList, containerType, modelAccessor, modelType, propertyName);


//Bind DescriptionAttribute
var description = attributeList.SingleOrDefault(a => typeof(DescriptionAttribute) == a.GetType());
if (description != null)
{
data.Description = ((DescriptionAttribute)description).Description;
}


return data;
}
}

这需要在 Global.asax.cs的 Application_Start方法中注册:

ModelMetadataProviders.Current = new ExtendedModelMetadataProvider();
小开 
@ViewData.ModelMetadata.Properties
.Where(m => m.PropertyName == "Phone1").FirstOrDefault().Description

所以，如果你使用自举程序，比如

<div class="form-group col-sm-6">
@Html.LabelFor(m => m.Organization.Phone1)
@Html.EditorFor(m => m.Organization.Phone1)
<p class="help-block">
@ViewData.ModelMetadata.Properties
.Where(m => m.PropertyName == "DayCount").FirstOrDefault().Description
</p>
</div>
小开

在 ASP.NET MVC 核心中，你可以使用新的标记帮助器，这使你的 HTML 看起来像... HTML:)

像这样:

<div class="form-group row">
<label asp-for="Name" class="col-md-2 form-control-label"></label>
<div class="col-md-10">
<input asp-for="Name" class="form-control" aria-describedby="Name-description" />
<span asp-description-for="Name" class="form-text text-muted" />
<span asp-validation-for="Name" class="text-danger" />
</div>
</div>

注意1: 可以在 input 元素中使用 aria-describedby属性，因为 id 将在 span 元素中使用 asp-description-for属性自动创建。

注意2: 在 Bootstrap 4中，类 form-text和 text-muted替换了块级帮助文本的 v3 help-block类。

要实现这个奇迹，只需创建一个新的标记帮助器:

using System;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Razor.TagHelpers;


/// <summary>
/// <see cref="ITagHelper"/> implementation targeting &lt;span&gt; elements with an <c>asp-description-for</c> attribute.
/// Adds an <c>id</c> attribute and sets the content of the &lt;span&gt; with the Description property from the model data annotation DisplayAttribute.
/// </summary>
[HtmlTargetElement("span", Attributes = DescriptionForAttributeName)]
public class SpanDescriptionTagHelper : TagHelper
{
private const string DescriptionForAttributeName = "asp-description-for";


/// <summary>
/// Creates a new <see cref="SpanDescriptionTagHelper"/>.
/// </summary>
/// <param name="generator">The <see cref="IHtmlGenerator"/>.</param>
public SpanDescriptionTagHelper(IHtmlGenerator generator)
{
Generator = generator;
}


/// <inheritdoc />
public override int Order
{
get
{
return -1000;
}
}


[HtmlAttributeNotBound]
[ViewContext]
public ViewContext ViewContext { get; set; }


protected IHtmlGenerator Generator { get; }


/// <summary>
/// An expression to be evaluated against the current model.
/// </summary>
[HtmlAttributeName(DescriptionForAttributeName)]
public ModelExpression DescriptionFor { get; set; }


/// <inheritdoc />
/// <remarks>Does nothing if <see cref="DescriptionFor"/> is <c>null</c>.</remarks>
public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
{
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}


if (output == null)
{
throw new ArgumentNullException(nameof(output));
}


var metadata = DescriptionFor.Metadata;


if (metadata == null)
{
throw new InvalidOperationException(string.Format("No provided metadata ({0})", DescriptionForAttributeName));
}


output.Attributes.SetAttribute("id", metadata.PropertyName + "-description");


if( !string.IsNullOrWhiteSpace( metadata.Description))
{
output.Content.SetContent(metadata.Description);
output.TagMode = TagMode.StartTagAndEndTag;
}
}
}

并使你的标签助手可用于我们所有的 Razor 视图:

@addTagHelper "*, YourAssemblyName"

注意1: 用项目的程序集名称替换 YourAssemblyName。

注2: 对于所有的标记帮助器，您只需要执行一次此操作！

更多有关标签助手的资料(只提供英文版本) : Https://docs.asp.net/en/latest/mvc/views/tag-helpers/intro.html

就是这样! 祝你和新的标签助手玩得开心！

小开

... 如果你喜欢把描述作为表单标签中的工具提示，添加一个标签助手如下:

using System;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Razor.TagHelpers;


/// <summary>
/// <see cref="ITagHelper"/> implementation targeting &lt;label&gt; elements with an <c>asp-for</c> attribute.
/// Adds a <c>title</c> attribute to the &lt;label&gt; with the Description property from the model data annotation DisplayAttribute.
/// </summary>
[HtmlTargetElement("label", Attributes = ForAttributeName)]
public class LabelTitleTagHelper : TagHelper
{
private const string ForAttributeName = "asp-for";


/// <summary>
/// Creates a new <see cref="LabelTitleTagHelper"/>.
/// </summary>
/// <param name="generator">The <see cref="IHtmlGenerator"/>.</param>
public LabelTitleTagHelper(IHtmlGenerator generator)
{
Generator = generator;
}


/// <inheritdoc />
public override int Order
{
get
{
return -1000;
}
}


[HtmlAttributeNotBound]
[ViewContext]
public ViewContext ViewContext { get; set; }


protected IHtmlGenerator Generator { get; }


/// <summary>
/// An expression to be evaluated against the current model.
/// </summary>
[HtmlAttributeName(ForAttributeName)]
public ModelExpression TitleFor { get; set; }


/// <inheritdoc />
/// <remarks>Does nothing if <see cref="TitleFor"/> is <c>null</c>.</remarks>
public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
{
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}


if (output == null)
{
throw new ArgumentNullException(nameof(output));
}


var metadata = TitleFor.Metadata;


if (metadata == null)
{
throw new InvalidOperationException(string.Format("No provided metadata ({0})", ForAttributeName));
}


if (!string.IsNullOrWhiteSpace(metadata.Description))
output.Attributes.SetAttribute("title", metadata.Description);
}
}

这将从模型的数据注释 DisplayAttribute中创建一个具有 Description属性的新 title属性。

美丽的部分是，您不需要触摸您生成的搭建的视图！因为这个标签帮助器的目标是 label元素的 asp-for属性，而这个属性已经存在了！

小开

HANDL 的回答，为 ASP.NET Core 2.0更新

using System;
using System.Linq.Expressions;
using Microsoft.AspNetCore.Html;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures.Internal;


public static class HtmlExtensions
{
public static IHtmlContent DescriptionFor<TModel, TValue>(this IHtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression)
{
if (html == null) throw new ArgumentNullException(nameof(html));
if (expression == null) throw new ArgumentNullException(nameof(expression));


var modelExplorer = ExpressionMetadataProvider.FromLambdaExpression(expression, html.ViewData, html.MetadataProvider);
if (modelExplorer == null) throw new InvalidOperationException($"Failed to get model explorer for {ExpressionHelper.GetExpressionText(expression)}");


return new HtmlString(modelExplorer.Metadata.Description);
}
}
小开

您总是可以创建自己的自定义扩展，如下所示:

    public static MvcHtmlString ToolTipLabel (string resourceKey, string text, bool isRequired, string labelFor = "", string labelId = "",string className="")
{
string tooltip = string.Empty;


StringBuilder sb = new StringBuilder();


if (!string.IsNullOrEmpty(resourceKey))
{
var resources = GetAllResourceValues();


if (resources.ContainsKey(resourceKey))
{
tooltip = resources[resourceKey].Value;
}
}


sb.Append("<label");


if (!string.IsNullOrEmpty(labelFor))
{
sb.AppendFormat(" for=\"{0}\"", labelFor);
}


if (!string.IsNullOrEmpty(labelId))
{
sb.AppendFormat(" Id=\"{0}\"", labelId);
}


if (!string.IsNullOrEmpty(className))
{
sb.AppendFormat(" class=\"{0}\"", className);
}


if (!string.IsNullOrEmpty(tooltip))
{


sb.AppendFormat(" data-toggle='tooltip' data-placement='auto left' title=\"{0}\"",tooltip);


}
if (isRequired)
{
sb.AppendFormat("><em class='required'>*</em> {0} </label></br>", text);
}
else
{
sb.AppendFormat(">{0}</label></br>", text);
}
return MvcHtmlString.Create(sb.ToString());
}

并且可以像这样看到它:

@HtmlExtension.ToolTipLabel(" "," ",true," "," "," ")
小开

如果有人想知道如何使用 接受的答案

1-在您的解决方案资源管理器 > 添加新文件夹 > 命名为“ Helpers”，例如
2-添加一个新类，例如将其命名为“ CustomHtmlHelpers”
粘贴代码: < br/> 

public static class MvcHtmlHelpers
{
public static string DescriptionFor<TModel, TValue>(this HtmlHelper<TModel> self, Expression<Func<TModel, TValue>> expression)
{
var metadata = ModelMetadata.FromLambdaExpression(expression, self.ViewData);
var description = metadata.Description;


return string.IsNullOrWhiteSpace(description) ? "" : description;
}
}

4-在你的模型或视图中使用它:

[Display(Name = "User Name", Description = "Enter your User Name")]
public string FullName { get; set; }

5-在 Razor 视图中，在@model 之后，键入这一行

@using YOUR_PROJECT.Helpers

6-像下面这样显示描述:

@Html.DescriptionFor(m => m.FullName)

你可能需要使用描述来在输入占位符中显示文本:

@Html.DisplayNameFor(m => m.FullName)
@Html.TextBoxFor(m => m.FullName, new { @class = "form-control", placeholder = Html.DescriptionFor(m => m.FullName) })

谢谢

小开

下面是 ASP.NET Core 3.1和5的更新版本:

public static class HtmlExtensions
{
public static IHtmlContent DescriptionFor<TModel, TValue>(this IHtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression)
{
if (html == null) throw new ArgumentNullException(nameof(html));
if (expression == null) throw new ArgumentNullException(nameof(expression));


var expressionProvider = html.ViewContext?.HttpContext?.RequestServices?.GetService<ModelExpressionProvider>()
?? new ModelExpressionProvider(html.MetadataProvider);
var modelExpression = expressionProvider.CreateModelExpression(html.ViewData, expression);


return new HtmlString(modelExpression.Metadata.Description);
}
}

我们必须通过 ModelExpressionProvider现在 ExpressionMetadataProvider是标记内部。

ModelExpressionProvider.CreateModelExpression()在内部呼叫 ExpressionMetadataProvider.FromLambdaExpression():

Https://github.com/aspnet/Mvc/blob/04ce6cae44fb0cb11470c21769d41e3f8088e8aa/src/microsoft ，AspNetCore，Mvc，ViewFeatures/ modelexpressionprovider.cs # l42


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