如何显示 DisplayAttribute.Description 属性值
本文关键字:DisplayAttribute Description 属性 显示 何显示 | 更新日期: 2023-09-27 18:01:01
我有一个模型类,具有这样的属性:
[Display(Name = "Phone", Description="Hello World!")]
public string Phone1 { get; set; }
在我的视图中显示标签并呈现文本框以供输入非常简单:
@Html.LabelFor(model => model.Organization.Phone1)
@Html.EditorFor(model => model.Organization.Phone1)
@Html.ValidationMessageFor(model => model.Organization.Phone1)
但是如何呈现描述注释属性的值,即"Hello World!"??
我最终得到了一个这样的助手:
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));
}
}
感谢那些带领我走向正确方向的人。 :)
使用本文中有关如何显示表单中字段的视觉提示的技术,可以通过以下方法访问该值:
@Html.TextBoxFor(
model => model.Email ,
new { title = ModelMetadata.FromLambdaExpression<RegisterModel , string>(
model => model.Email , ViewData ).Description } )
在 ASP.NET MVC Core中,您可以使用新的标记帮助程序,这使您的HTML看起来像...网页:)
喜欢这个:
<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:您可以在输入元素中使用 aria-describedby
属性,因为该 id 将在具有 asp-description-for
属性的 span 元素中自动创建。
注意 2:在 Bootstrap 4 中,类form-text
和text-muted
替换块级帮助文本的 v3 help-block
类。
要实现这种魔术,您只需创建一个新的标记帮助程序:
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 <span> elements with an <c>asp-description-for</c> attribute.
/// Adds an <c>id</c> attribute and sets the content of the <span> 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;
}
}
}
并使您的标签帮助程序可用于我们所有的 Razor 视图。将 addTagHelper 指令添加到Views/_ViewImports.cshtml
文件:
@addTagHelper "*, YourAssemblyName"
注意 1:将YourAssemblyName
替换为项目的程序集名称。
注意2:您只需要为所有标记助手执行此操作一次!
有关标记帮助程序的详细信息,请参阅此处:https://docs.asp.net/en/latest/mvc/views/tag-helpers/intro.html
就是这样!与新的标签助手一起玩得开心!
我正要使用接受的答案,但它不适用于 ASP.NET Core 1/2(又名 MVC 6(,ModelMetadata.FromLambdaExpression
因为它不再存在并且已移至ExpressionMetadataProvider
(用法也略有改变(。
这是可用于 ASP.NET Core 1.1和2的更新扩展方法:
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 核心 1
对于 ASP.NET Core 1,相同的代码有效,但您需要不同的命名空间usings
:
using System;
using System.Linq.Expressions;
using Microsoft.AspNet.Html.Abstractions;
using Microsoft.AspNet.Mvc.ViewFeatures;
用法
@Html.DescriptionFor(model => model.Phone1)
如果有人想知道如何使用接受的答案
1-在解决方案资源管理器中,>添加新文件夹>将其命名为"帮助程序",例如
2-添加一个新类,将其命名为"CustomHtmlHelpers",例如
3-粘贴代码:
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-在您的模型或视图中使用它的模型:
[Display(Name = "User Name", Description = "Enter your User Name")]
public string FullName { get; set; }
5-在Razor视图中,在@model之后,键入此行
@using YOUR_PROJECT.Helpers
6-显示如下描述:
@Html.DescriptionFor(m => m.FullName)
7-您可能希望使用描述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
var attrib = (DisplayAttribute)Attribute.GetCustomAttribute(
member, typeof(DisplayAttribute));
var desc = attrib == null ? "" : attrib.GetDescription()
以下是 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
,因为ExpressionMetadataProvider
被标记为内部。
无论如何,ModelExpressionProvider.CreateModelExpression()
内部调用ExpressionMetadataProvider.FromLambdaExpression()
:
https://github.com/aspnet/Mvc/blob/04ce6cae44fb0cb11470c21769d41e3f8088e8aa/src/Microsoft.AspNetCore.Mvc.ViewFeatures/ModelExpressionProvider.cs#L42
@ViewData.ModelMetadata.Properties
.Where(m => m.PropertyName == "Phone1").FirstOrDefault().Description
所以,如果你使用的是引导程序,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>
您必须编写一个自定义帮助程序来反映您的模型,以提供 Description 属性值。
...如果您希望将描述作为表单标签中的工具提示,请添加如下所示的标记帮助程序:
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 <label> elements with an <c>asp-for</c> attribute.
/// Adds a <c>title</c> attribute to the <label> 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);
}
}
这将创建一个新的title
属性,其中包含模型的数据注释DisplayAttribute
中的 Description
属性。
美丽的部分是您无需触摸生成的脚手架视图!因为此标记帮助程序的目标是已经存在的label
元素的asp-for
属性!
除了Jakob Gade'一个很好的答案:
如果您需要 支持DescriptionAttribute
而不是DisplayAttribute
,如果我们覆盖元数据提供程序,他的出色解决方案仍然有效:
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
方法中寄存器:
ModelMetadataProviders.Current = new ExtendedModelMetadataProvider();
HANDL的答案,针对 ASP.NET 核心2.0进行了更新
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);
}
}
您始终可以像这样创建自己的自定义扩展:
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());
}
并且可以像这样查看它:
@HtmlExtension.ToolTipLabel(" "," ",true," "," "," ")