为什么Razor页面脚手架将HTML帮助器(而不是标签帮助器)用于索引，详细信息和删除页面?

问题描述

我最近使用Razor Pages开始了我的第一个项目，我使用的是EF Core，并将我的所有模型都放入CRUD Razor Pages中.我注意到的是，生成的创建和编辑剃刀页面"使用标签助手"来显示数据.即

I recently started my first project using Razor Pages, I am using EF Core and have scaffolded all of my models into CRUD Razor Pages. Something I noticed was that the Create and Edit Razor Pages that are generated use Tag Helpers to display the data. i.e.

        <div class="form-group">
            <label asp-for="ViewModel.Name" class="control-label"></label>
            <input asp-for="ViewModel.Name" class="form-control" />
            <span asp-validation-for="ViewModel.Name" class="text-danger"></span>
        </div>

索引，详细信息和删除页面使用Html帮助器显示数据.即

Whereas the Index, Details, and Delete Pages use Html Helpers to display the data. i.e.

    <dt>
        @Html.DisplayNameFor(model => model.ViewModel.Name)
    </dt>
    <dd>
        @Html.DisplayFor(model => model.ViewModel.Name)
    </dd>

此 Microsoft的链接说:标记助手减少了Razor视图中HTML和C#之间的显式转换.在许多情况下，HTML助手为特定的标记助手提供了另一种方法，但重要的是要认识到标记助手不会替换HTML Helper，并且每个HTML Helper都没有一个Tag Helper.".

This link from Microsoft says that "Tag Helpers reduce the explicit transitions between HTML and C# in Razor views. In many cases, HTML Helpers provide an alternative approach to a specific Tag Helper, but it's important to recognize that Tag Helpers don't replace HTML Helpers and there's not a Tag Helper for each HTML Helper.".

但是这些基本显示字段当然可以与Tag Helpers一起显示.在我看来，这似乎是一个相当琐碎的不一致之处，我认为最好是仅在绝对需要时才使用Tag Helpers和Html Helpers，这是更好的做法.

But certainly these basic display fields could be displayed with Tag Helpers. This seems to me like a rather frivolous inconsistency and I would think that it would be better practice to use Tag Helpers primarily and Html Helpers only when absolutely neccecary.

我认为开发人员有这样做的理由，但是我可能没有想到.有人可以帮我照一下吗?

I assume that the developers had a reason for doing it this way, but what that might be escapes me. Could anyone please shine some light on this for me please?

推荐答案

简单:没有标签助手可以显示.

Simple: there's no tag helpers for display.

展开:

为输入之类的东西配备标签助手是很有意义的:与之关联的是特定的HTML标签.显示会使事情变得更加模糊.每个开发人员都可能希望使用不同的标签来显示:span，strong，th，dt等.这里没有一种适合的尺寸.您甚至可能根本不需要标签.默认情况下，Html.DisplayFor和Html.DisplayNameFor仅输出值，不带任何标签.

Having tag helpers for things like inputs makes sense: there's specific HTML tags associated with that. Things get a lot more blurry with display. Each individual developer might want to use different tags for display: span, strong, th, dt, etc. There's no one-size fits all here. You might not even want a tag at all. By default Html.DisplayFor and Html.DisplayNameFor just output the values, without any tags.

此外，这些都是模板化的帮助程序，这意味着您作为开发人员可以实际将模板添加到Views\Shared\DisplayTemplates并自定义事物的显示方式.例如，您可以在String.cshtml视图中输入类似以下内容:

Also, these are templated helpers, which means you as a developer can actually add templates to Views\Shared\DisplayTemplates and customize how things are displayed. For example, you could at a String.cshtml view there, with something like:

@model string
<strong>@Model</strong>

现在，使用Html.DisplayFor显示的任何字符串属性都将包装在strong标记中.标签助手无法实现这种级别的自定义.

And now, any string property displayed using Html.DisplayFor would be wrapped in strong tags. This level of customization wouldn't be possible with tag helpers.

编辑

FWIW，如果您真的想使用标签助手，则可以添加自己的标签助手.例如:

FWIW, if you really want to use tag helpers, you can just add your own. For example:

public class DisplayNameTagHelper : TagHelper
{
    public ModelExpression For { get; set; }

    public override void Process(TagHelperContext context, TagHelperOutput output)
    {
        output.TagName = "strong";
        output.Content.SetContent(For.Metadata.DisplayName);
    }
}

然后在您看来:

<display-name for="MyProperty" />

写DisplayTagHelper在概念上类似，但难度更高.您可以从For.Model获取值.但是，将其键入为object.使用For.Metadata上可用的信息，您需要确定实际使用的对象，并且可能有几个不同的分支，以根据类型显示不同的内容.在小数点，日期时间等方面也需要考虑For.Metadata.DataFormatString.

Writing a DisplayTagHelper would be similar in concept, but a bit more difficult. You can get the value from For.Model. However, this is typed as object. Using information available on For.Metadata, you'd need to determine what you're actually working with and probably have a few different branches to display things differently depending on the type. There's also For.Metadata.DataFormatString that would need to be taken into account with things like decimals, DateTimes, etc.

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