c# - 嵌入在另一个标签助手代码中的标签助手不呈现

Question

我正在尝试使用 .net Core 2.0 中的以下自定义标签助手来简化长表单的创建:

@model ObApp.Web.Models.ViewComponents.FormFieldViewModel

<span>Debug - Paramater value: @Model.FieldFor</span>
<div class="form-group">
    <label asp-for="@Model.FieldFor"></label>
    <input asp-for="@Model.FieldFor" class="form-control" />
</div>

这看起来很简单，但是当我使用时我得到了意想不到的结果:

<vc:form-field field-for="PersonEmail"></vc:form-field>

预期结果

<span>Debug - Paramater value: PersonEmail</span>
<div class="form-group">
    <label for="PersonEmail">Email</label>
    <input name="PersonEmail" class="form-control" id="PersonEmail" 
        type="text" value="PersonEmail">
</div>

实际结果

<span>Debug - Paramater value: PersonEmail</span>
<div class="form-group">
    <label for="FieldFor">FieldFor</label>
    <input name="FieldFor" class="form-control" id="FieldFor" 
        type="text" value="PersonEmail">
</div>

我已经尝试从 @Model.FieldFor 周围删除引号，以及一些其他语法更改。

有什么建议吗？

谢谢!

Answer 1

正如其他人向我指出的那样，可能无法按照我发布此问题时最初希望的方式直接嵌入标签助手。因此，我重构了代码，改为以编程方式“更新”所需的标签助手。

我的最终解决方案比我预期的要多得多，但从长远来看，它将节省大量时间来开发我计划的表单密集型应用程序。

目标

我的目标是通过使用这个自定义标签助手来加速表单的创建，例如:

<formfield asp-for="OrganizationName"></formfield>

要生成这些内置的 Razor 标签助手:

<div class="form-group">
    <div class="row">
        <label class="col-md-3 col-form-label" for="OrganizationName">Company Name</label>
        <div class="col-md-9">
            <input name="OrganizationName" class="form-control" id="OrganizationName" type="text" value="" data-val-required="The Company Name field is required." data-val="true" data-val-maxlength-max="50" data-val-maxlength="Maximum company name length is 50 characters.">
            <span class="field-validation-valid" data-valmsg-replace="true" data-valmsg-for="OrganizationName"></span>
        </div>
    </div>
</div>

我最初的工作解决方案

这是针对简单案例的首轮测试解决方案。 IE。对于默认的硬编码类和文本框输入类型。

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

namespace ObApp.Web.TagHelpers
{
    // Builds form elements to generate the following (for example):
    // <div class="form-group">
    //     <div class="row">
    //         <input ... >Email</input>
    //         <div>
    //             <input type="text" ... />
    //             <span class="field-validation-valid ... ></span>
    //         </div>
    //     </div>
    // </div>

    public class FormfieldTagHelper : TagHelper
    {
        private const string _forAttributeName = "asp-for";
        private const string _defaultWraperDivClass = "form-group";
        private const string _defaultRowDivClass = "row";
        private const string _defaultLabelClass = "col-md-3 col-form-label";
        private const string _defaultInputClass = "form-control";
        private const string _defaultInnerDivClass = "col-md-9";
        private const string _defaultValidationMessageClass = "";

        public FormfieldTagHelper(IHtmlGenerator generator)
        {
            Generator = generator;
        }

        [HtmlAttributeName(_forAttributeName)]
        public ModelExpression For { get; set; }

        public IHtmlGenerator Generator { get; }

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

        public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
        {
            // Replace this parent tag helper with div tags wrapping the entire form block
            output.TagName = "div";
            output.Attributes.SetAttribute("class", _defaultWraperDivClass);

            // Manually new-up each child asp form tag helper element
            TagHelperOutput labelElement = await CreateLabelElement(context);
            TagHelperOutput inputElement = await CreateInputElement(context);
            TagHelperOutput validationMessageElement = await CreateValidationMessageElement(context);

            // Wrap input and validation with column div
            IHtmlContent innerDiv = WrapElementsWithDiv(
                    new List<IHtmlContent>()
                    {
                        inputElement,
                        validationMessageElement
                    },
                    _defaultInnerDivClass
                );

            // Wrap all elements with a row div
            IHtmlContent rowDiv = WrapElementsWithDiv(
                    new List<IHtmlContent>()
                    {
                        labelElement,
                        innerDiv
                    },
                    _defaultRowDivClass
                );

            // Put everything into the innerHtml of this tag helper
            output.Content.SetHtmlContent(rowDiv);
        }

        private async Task<TagHelperOutput> CreateLabelElement(TagHelperContext context)
        {
            LabelTagHelper labelTagHelper = 
                new LabelTagHelper(Generator)
                {
                    For = this.For,
                    ViewContext = this.ViewContext
                };

            TagHelperOutput labelOutput = CreateTagHelperOutput("label");

            await labelTagHelper.ProcessAsync(context, labelOutput);

            labelOutput.Attributes.Add(
                new TagHelperAttribute("class", _defaultLabelClass));

            return labelOutput;
        }

        private async Task<TagHelperOutput> CreateInputElement(TagHelperContext context)
        {
            InputTagHelper inputTagHelper = 
                new InputTagHelper(Generator)
                {
                    For = this.For,
                    ViewContext = this.ViewContext
                };

            TagHelperOutput inputOutput = CreateTagHelperOutput("input");

            await inputTagHelper.ProcessAsync(context, inputOutput);

            inputOutput.Attributes.Add(
                new TagHelperAttribute("class", _defaultInputClass));

            return inputOutput;
        }

        private async Task<TagHelperOutput> CreateValidationMessageElement(TagHelperContext context)
        {
            ValidationMessageTagHelper validationMessageTagHelper = 
                new ValidationMessageTagHelper(Generator)
                {
                    For = this.For,
                    ViewContext = this.ViewContext
                };

            TagHelperOutput validationMessageOutput = CreateTagHelperOutput("span");

            await validationMessageTagHelper.ProcessAsync(context, validationMessageOutput);

            return validationMessageOutput;
        }

        private IHtmlContent WrapElementsWithDiv(List<IHtmlContent> elements, string classValue)
        {
            TagBuilder div = new TagBuilder("div");
            div.AddCssClass(classValue);
            foreach(IHtmlContent element in elements)
            {
                div.InnerHtml.AppendHtml(element);
            }

            return div;
        }

        private TagHelperOutput CreateTagHelperOutput(string tagName)
        {
            return new TagHelperOutput(
                tagName: tagName,
                attributes: new TagHelperAttributeList(),
                getChildContentAsync: (s, t) =>
                {
                    return Task.Factory.StartNew<TagHelperContent>(
                            () => new DefaultTagHelperContent());
                }
            );
        }
    }
}

后续步骤/改进建议

这适用于没有验证错误的文本框。调整默认 CSS 后，我计划采取的后续步骤是:

1. 在出现验证错误时显示用于格式设置的正确 CSS 类属性。此时标签助手将为我“工作”。
2. 将硬编码的 CSS 类移到站点配置文件中。
3. 绑定(bind)到 View 中的 HTML 属性以允许传入非默认类。另一种方法是通过 ViewModel 传入非默认表单类。
4. 检测非文本框输入类型并相应地设置格式。

感谢@Chris Pratt 让我开始朝着正确的方向前进。