在 ASP.NET MVC 3 中添加您自己的 HtmlHelper

Question

我是 MVC 的新手，我正在尝试创建自己的扩展方法，以便可以添加到我的 razor 视图中可用的 html 帮助程序中。 Html.DropDownListFor() 允许您为模型上的任何属性创建一个下拉列表。我想创建一个名为Html.StateDropDownListFor() 的助手，它做同样的事情，除了加载美国所有 50 个州的下拉菜单。这样我就不必为我创建的每个状态下拉列表创建一个 SelectList。最简单的方法是什么？现在我有这个：

public static class ExtensionMethods
{
    public static MvcHtmlString StateDropDownList(this HtmlHelper html)
    {
        // ???
    }
}

我什至接近吗？我不想重建整个文本框助手，我只想创建一个利用现有文本框助手但为我执行 SelectList 的助手。在我看来，这样我就可以做到Html.StateDropDownList(x => x.State)

Answer 1

（代表问题作者发布解决方案，将其移至答案部分）。

这就是答案！

这是完整的扩展方法，以防其他人使用它。

    public static MvcHtmlString StateDropDownListFor<TModel, TValue>(this HtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression)
    {
        Dictionary<string, string> stateList = new Dictionary<string, string>()
        {
            {"AL"," Alabama"},
            {"AK"," Alaska"},
            {"AZ"," Arizona"},
            {"AR"," Arkansas"},
            {"CA"," California"},
            {"CO"," Colorado"},
            {"CT"," Connecticut"},
            {"DE"," Delaware"},
            {"FL"," Florida"},
            {"GA"," Georgia"},
            {"HI"," Hawaii"},
            {"ID"," Idaho"},
            {"IL"," Illinois"},
            {"IN"," Indiana"},
            {"IA"," Iowa"},
            {"KS"," Kansas"},
            {"KY"," Kentucky"},
            {"LA"," Louisiana"},
            {"ME"," Maine"},
            {"MD"," Maryland"},
            {"MA"," Massachusetts"},
            {"MI"," Michigan"},
            {"MN"," Minnesota"},
            {"MS"," Mississippi"},
            {"MO"," Missouri"},
            {"MT"," Montana"},
            {"NE"," Nebraska"},
            {"NV"," Nevada"},
            {"NH"," New Hampshire"},
            {"NJ"," New Jersey"},
            {"NM"," New Mexico"},
            {"NY"," New York"},
            {"NC"," North Carolina"},
            {"ND"," North Dakota"},
            {"OH"," Ohio"},
            {"OK"," Oklahoma"},
            {"OR"," Oregon"},
            {"PA"," Pennsylvania"},
            {"RI"," Rhode Island"},
            {"SC"," South Carolina"},
            {"SD"," South Dakota"},
            {"TN"," Tennessee"},
            {"TX"," Texas"},
            {"UT"," Utah"},
            {"VT"," Vermont"},
            {"VA"," Virginia"},
            {"WA"," Washington"},
            {"WV"," West Virginia"},
            {"WI"," Wisconsin"},
            {"WY"," Wyoming"},
            {"AS"," American Samoa"},
            {"DC"," District of Columbia"},
            {"FM"," Federated States of Micronesia"},
            {"MH"," Marshall Islands"},
            {"MP"," Northern Mariana Islands"},
            {"PW"," Palau"},
            {"PR"," Puerto Rico"},
            {"VI"," Virgin Islands"},
            {"GU"," Guam"}
        };
        return html.DropDownListFor(expression, new SelectList(stateList, "key", "value"));
    }

我修改了上面的代码，使用字典来表示州的缩写。

别忘了在扩展方法类的顶部引用System.Web.Mvc.Html，就像我忘记的那样。

Answer 2

要在 Razor 视图中使用自定义辅助方法，您需要将其纳入范围。有两种可能的方法来做到这一点：

1. 在视图顶部添加一个@using SomeNamespace，并在其中定义包含帮助器的静态类的命名空间

2. 在~/Views/web.config 中，添加：

   <system.web.webPages.razor>
       <host factoryType="System.Web.Mvc.MvcWebRazorHostFactory, System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
           <pages pageBaseType="System.Web.Mvc.WebViewPage">
               <namespaces>
                   <add namespace="System.Web.Mvc" />
                   <add namespace="System.Web.Mvc.Ajax" />
                   <add namespace="System.Web.Mvc.Html" />
                   <add namespace="System.Web.Routing" />
                   <add namespace="SomeNamspace" />
               </namespaces>
           </pages>
       </system.web.webPages.razor>
   

一旦自定义帮助器进入视图范围，Intellisense 应该能够选择它并且您可以使用它：

@Html.StateDropDownList()

现在你的辅助方法需要做一些有用的事情。您可以调用现有的助手：

public static class ExtensionMethods
{
    public static MvcHtmlString StateDropDownList(this HtmlHelper html)
    {
        return html.TextBox("foo")
    }
}

或返回一些自定义数据：

public static class ExtensionMethods
{
    public static MvcHtmlString StateDropDownList(this HtmlHelper html)
    {
        return MvcHtmlString.Create("Hello world");
    }
}

如果你有一个强类型视图并且你想使用表达式：

using System.Web.Mvc;
using System.Web.Mvc.Html;

public static class ExtensionMethods
{
    public static MvcHtmlString StateDropDownList(
        this HtmlHelper<MyViewModel> html
    )
    {
        var stateList = new SelectList(new[]
        {
            new { Key = "Alabama", Value = "Alabama" },
            new { Key = "Idaho", Value = "Idaho" },
            new { Key = "California", Value = "California" }
        }, "Key", "Value");
        return Html.DropDownListFor(
            x => x.State, stateList, "-- Select a state --"
        );
    }
}

然后：

@Html.StateDropDownList()

Answer 3

using System.Web.Mvc.Html;
public static MvcHtmlString StateDropDownList<TModel, TValue>( this HtmlHelper<TModel> html,
    Expression<Func<TModel, TValue>> expression ) {
        return html.DropDownListFor( expression, _stateList );
}

会工作的。 _stateList 是 IEnumerable<SelectListItem>。