ASP.NET MVC中自定义一个HtmlHelper方法

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以Label()方法为例，查看Label方法的定义：

internal static MvcHtmlString LabelHelper(HtmlHelper html, ModelMetadata metadata, string htmlFieldName, string labelText = null, IDictionary htmlAttributes = null){            string resolvedLabelText = labelText ?? metadata.DisplayName ?? metadata.PropertyName ?? htmlFieldName.Split('.').Last();            if (String.IsNullOrEmpty(resolvedLabelText))            {                return MvcHtmlString.Empty;            }            TagBuilder tag = new TagBuilder("label");            tag.Attributes.Add("for", TagBuilder.CreateSanitizedId(html.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(htmlFieldName)));            tag.SetInnerText(resolvedLabelText);            tag.MergeAttributes(htmlAttributes, replaceExisting: true);            return tag.ToMvcHtmlString(TagRenderMode.Normal);}

这是MVC的源码中对Label()扩展方法的定义，我们可以参考MVC中源码定义扩展方法的方式自定义一个扩展方法。

下面以span标签为例进行扩展，扩展方法定义如下：

using System;using System.Collections.Generic;using System.Linq;using System.Web;using System.Web.Mvc;namespace MvcHtmlHelper.Helper{    /// 
    /// HTML的扩展类    /// 
    public static class HtmlHelperExt    {        /// 
        /// 用C#代码自定义一个span标签的扩展方法        /// 
        ///         ///         ///         ///         ///         ///         public static MvcHtmlString Messager(this HtmlHelper htlper, string id,string name, string style, object message)        {            if (message != null)            {                TagBuilder builder = new TagBuilder("span");                builder.MergeAttribute("style", style); //定义样式                builder.MergeAttribute("id", id);     // 定义Id                builder.MergeAttribute("name", name);  // 定义name                builder.SetInnerText(message.ToString());                //ToMvcHtmlString是在TagBuilderExtensions扩展类中定义的                return builder.ToMvcHtmlString(TagRenderMode.Normal);            }            return MvcHtmlString.Empty;        }    }}

TagBuilderExtensions扩展方法定义如下：

using System;using System.Collections.Generic;using System.Linq;using System.Web;using System.Web.Mvc;namespace MvcHtmlHelper.Helper{    public static class TagBuilderExtensions    {        public static MvcHtmlString ToMvcHtmlString(this TagBuilder tagBuilder, TagRenderMode renderMode)        {            System.Diagnostics.Debug.Assert(tagBuilder != null);            return new MvcHtmlString(tagBuilder.ToString(renderMode));        }    }}

视图页面代码如下：

@using MvcHtmlHelper.Helper;@{    ViewBag.Title = "Home Page";}
    
ASP.NET
    
ASP.NET is a free web framework for building great Web sites and Web applications using HTML, CSS and JavaScript.
    
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                @Html.Messager("lblMessage", "lblMessage", "color:red;font-weight:bold;", "自定义span标签")    
    
        
Getting started
        
            ASP.NET MVC gives you a powerful, patterns-based way to build dynamic websites that            enables a clean separation of concerns and gives you full control over markup            for enjoyable, agile development.        
        
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运行结果如下：

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