ASP.NET 5 MVC 6中的单选按钮标记帮助程序

所有输入类型都有一个TagHelper，其中也包括单选按钮类型。假设你有一个像这样的视图模型

public class CreateUserVm
{
    public string UserName { set; get; }
    public IEnumerable<RoleVm> Roles { set; get; } 
    public int SelectedRole { set; get; }
}
public class RoleVm
{
    public int Id { set; get; }
    public string RoleName { set; get; }        
}

在你的GET行动中，

public IActionResult Index()
{
    var vm = new CreateUserVm
    {
        Roles = new List<RoleVm>
        {
            new RoleVm {Id = 1, RoleName = "Admin"},
            new RoleVm {Id = 2, RoleName = "Editor"},
            new RoleVm {Id = 3, RoleName = "Reader"}
        }
    };
    return View(vm);
}

在视图中，您可以简单地对输入标记使用标记。

@model YourNamespaceHere.CreateUserVm
<form asp-action="Index" asp-controller="Home">
    <label class="label">User name</label>
    <div class="col-md-10">
        <input type="text" asp-for="UserName" />
    </div>
    <label class="label">Select a Role</label>
    <div class="col-md-10">
    @foreach (var item in Model.Roles)
    {
       <input asp-for="SelectedRole" type="radio" value="@item.Id" /> @item.RoleName
    }
    </div>
    <input type="submit" />
</form>

当您发布表单时，所选角色的Rold Id将位于SelectedRole属性中

请记住，上面的剃刀代码将为循环生成的每个输入生成具有相同Id属性值和name属性值的输入元素。在上面的示例中，它将生成3个输入元素（单选按钮类型），其中Id和name属性值设置为SelectedRole。模型绑定将在name属性值与视图模型中的属性名称（SelectedRole）匹配时工作，但重复的Id属性值可能会给客户端代码带来麻烦（文档中重复的Id无效）

虽然有使用asp-for="SomeField"的解决方案，但我发现最简单的解决方案是将视图模型字段与单选按钮的name字段匹配。

视图模型：

public class MyViewModel
{
   public string MyRadioField { get; set; }
}

形式（为清晰起见，无标签）：

@model MyViewModel
<form asp-action="SomeAction" asp-controller="SomeController">
   <input type="radio" name="MyRadioField" value="option1" checked />
   <input type="radio" name="MyRadioField" value="option2" />
   <input type="radio" name="MyRadioField" value="option3" />
   <input type="submit" />
</form>

提交表单时，MyRadioField将填充选中单选按钮的值。

我已经编写了自己的标记助手来实现这一点。它将input标签替换为每个枚举变体的标签和单选按钮：

using System.Collections.Generic;
using System.Linq;
using System.Text;
using DigitScpi.Web.Helpers;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Razor.TagHelpers;
namespace TagHelpers
{
    /// Generates the radio buttons for an enum. Syntax: `<input radio asp-for="MyMappedEnumField"/>`.
    [HtmlTargetElement("input", Attributes = RadioAttributeName)]
    public class RadioButtonTagHelper : TagHelper
    {
        private const string RadioAttributeName = "radio";
        private const string ForAttributeName = "asp-for";
        [HtmlAttributeNotBound] [ViewContext] public ViewContext ViewContext { get; set; }
        private readonly IHtmlGenerator _generator;
        [HtmlAttributeName(ForAttributeName)] public ModelExpression For { get; set; }
        [HtmlAttributeName(RadioAttributeName)] public bool RadioMarker { get; set; }
        public RadioButtonTagHelper(IHtmlGenerator generator)
        {
            _generator = generator;
        }
        /// <inheritdoc />
        public override void Process(TagHelperContext context, TagHelperOutput output)
        {
            output.SuppressOutput();
            foreach (var enumItem in For.Metadata.EnumNamesAndValues)
            {
                var id = VariantId(enumItem);
                var name = For.Metadata.EnumGroupedDisplayNamesAndValues.FirstOrDefault(v => v.Value == enumItem.Value).Key.Name;
                var radio = _generator.GenerateRadioButton(ViewContext, For.ModelExplorer, For.Name, enumItem.Key, false, new {id});
                var label = _generator.GenerateLabel(ViewContext, For.ModelExplorer, For.Name, name, new {@for = id});
                output.PreElement.AppendHtml(radio);
                output.PreElement.AppendHtml(label);
            }
        }
        /// Computes the variant to be unique for each radiobutton.
        private string VariantId(KeyValuePair<string, string> enumItem) =>
            new StringBuilder()
                .Append(ViewContext.CreateUniqueId(_generator.IdAttributeDotReplacement, For.Name))
                .Append(_generator.IdAttributeDotReplacement)
                .Append(enumItem.Key)
                .ToString();
    }
}

这里有一个扩展方法，它在给定SelectList的情况下呈现单选按钮列表。你使用它就像使用Html.DropDownListFor 一样

public static HtmlString RadioButtonListFor<TModel, TResult>(this IHtmlHelper<TModel> helper, Expression<Func<TModel, TResult>> expression, SelectList selectList, string className = "radio-group")
{
  //render a list of radio buttons to bind to the specified value
  MemberExpression member = expression.Body as MemberExpression;
  string propertyName = member.Member.Name;
  Func<TModel, TResult> method = expression.Compile();
  TResult selectedValue = method(helper.ViewData.Model);
  var output = new StringBuilder();
  if (!string.IsNullOrEmpty(className))
    output.AppendLine($"<div class='{className}'>");
  else
    output.AppendLine("<div>");
  foreach (SelectListItem item in selectList)
  {
    bool selected = Convert.ToString(selectedValue) == item.Value;
    string html = $"<label> <input type='radio' name='{propertyName}' value='{item.Value}' {(selected ? "checked" : "")} /> {item.Text} </label>";
    output.AppendLine(html);
  }
  output.AppendLine("</div>");
  return new HtmlString(output.ToString());
}

你在剃刀文件中这样称呼它：

 @Html.RadioButtonListFor(m => m.ModelProperty, selectList)