[ASP.NET MVC]为HtmlHelper添加一个RadioButtonList扩展方法

在前面一篇文章中，我们通过对HtmlHelper的扩展简化了对DropDownList（Single-Line-Select）和ListBox（Multiple-Line-Select）的绑定，以及对作为数据源的列表进行单独维护。现在我们为HtmlHelper/HtmlHelper<Model>添加一个RadioButtonList/RadioButtonListFor扩展方法实现一组RadioButton的绑定。[源代码从这里下载]

一、RadioButtonListFor的使用

我们先来显示一下扩展的RadioButtonListFor的方法的用法。如下所示的是作为Model的Person类型，其Gender（Male/Female）、MaritalStatus（Single/Married）和Country的选项列表通过独立的组件CodeManager进行单独维护。

public class Person
{
    public string Name { get; set; }
    public string Gender { get; set; }
    [Display(Name = "Marital Status")]
    public string MaritalStatus { get; set; }
    public string Country { get; set; }
}

在一个针对Person对象进行编辑的强类型View（以Person作为Model）中我们进行了如下的定义。RadioButtonListFor方的最后一个参数（“Gender”、“MaritalStatus”和“Country”）表示对应列表的类别。

@using System.Web.UI.WebControls
@model Person
@{
    ViewBag.Title = "Index";
}
@using (Html.BeginForm())
{
    <table id="container">
        <tr>
            <td class="label">@Html.LabelFor(m => m.Name):</td>
            <td>@Html.EditorFor(m => m.Name)</td>
        </tr>
         <tr>
            <td class="label">@Html.LabelFor(m => m.Gender):</td>
            <td>@Html.RadioButtonListFor(m => m.Gender, "Gender")</td>
        </tr>
         <tr>
            <td class="label">@Html.LabelFor(m => m.MaritalStatus):</td>
            <td>@Html.RadioButtonListFor(m => m.MaritalStatus, "MaritalStatus")</td>
        </tr>
         <tr>
            <td class="label">@Html.LabelFor(m => m.Country):</td>
            <td>@Html.RadioButtonListFor(m => m.Country, "Country", RepeatDirection.Vertical)</td>
        </tr>
        <tr>
            <td colspan="2"><input type="submit" value="Save" /></td>
        </tr>
    </table>
}

下面这张图表示上面这个View在浏览器中呈现出来的样式，我们可以看到三组RadioButton被有效地生成出来。

二、维护选项列表的组件CodeManager

由于在一个应用中，作为绑定到“列表控件”上的选项列表可能会有很多，将它们进行单独地维护是一个理想的选择。作为模拟，我们创建了如下一个简单的CodeManager组件。我们将列表中的某个选项通过CodeDescription，其三个属性Code、Description分别表示其“值”和“显示文本”，Category表示类别（通过它对列表项进行分组）。CodeManager通过一个静态字段作为列表数据的存储，上面例子中使用到的三组列表维护于此。GetCodes方法用于返回指定“类别”的列表选项。

public class CodeDescription
{
    public string Code { get; set; }
    public string Description { get; set; }
    public string Category{get;set;}

    public CodeDescription(string code, string description, string category)
    {
        this.Code = code;
        this.Description = description;
        this.Category = category;
    }
}
public static class CodeManager
{
    private static CodeDescription[] codes = new CodeDescription[]
    {
        new CodeDescription("M","Male","Gender"),
        new CodeDescription("F","Female","Gender"),
        new CodeDescription("S","Single","MaritalStatus"),
        new CodeDescription("M","Married","MaritalStatus"),
        new CodeDescription("CN","China","Country"),
        new CodeDescription("US","Unite States","Country"),
        new CodeDescription("UK","Britain","Country"),
        new CodeDescription("SG","Singapore","Country")
    };
    public static Collection<CodeDescription> GetCodes(string category)
    {
        Collection<CodeDescription> codeCollection = new Collection<CodeDescription>();
        foreach(var code in codes.Where(code=>code.Category == category))
        {
            codeCollection.Add(code);
        }
        return codeCollection;
    }
}

三、RadioButtonList/RadioButtonListFor扩展方法

如下所示的是RadioButtonList/RadioButtonListFor两个扩展方法的定义，参数codeCategory表示作为数据源的列表类别，而RepeatDirection 枚举类型则代表同组的RadioButton的排列方向，默认为水平。从上面的例子我们可以看到，我们通过这个参数将名称为Country的RadioButtonList进行了纵向排列。通过Html生成代码我们可以看出，我们采用了Table作为布局方式，实际上ASP.NET的RadioButtonList也是这么做的。

public static  class RadioButtonListExtensions
{
    public static MvcHtmlString RadioButtonList(this HtmlHelper htmlHelper, string name,  string codeCategory, RepeatDirection repeatDirection = RepeatDirection.Horizontal, IDictionary<string, object> htmlAttributes = null)
    {
        var codes = CodeManager.GetCodes(codeCategory);
        return GenerateHtml(name, codes, repeatDirection, htmlAttributes, null);
    }
    public static MvcHtmlString RadioButtonListFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, string codeCategory, RepeatDirection repeatDirection =  RepeatDirection.Horizontal, IDictionary<string, object> htmlAttributes = null)
    {
        var codes = CodeManager.GetCodes(codeCategory);

        ModelMetadata metadata = ModelMetadata.FromLambdaExpression<TModel, TProperty>(expression, htmlHelper.ViewData);
        string name = ExpressionHelper.GetExpressionText(expression);
        var attributes = htmlHelper.GetUnobtrusiveValidationAttributes(name, metadata);
        foreach (var item in attributes)
        {
            htmlAttributes.Add(item);
        }
        string fullHtmlFieldName = htmlHelper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(name);
        string stateValue = (string)metadata.Model;
        return GenerateHtml(fullHtmlFieldName, codes, repeatDirection, htmlAttributes, stateValue);
    }
    private static MvcHtmlString GenerateHtml(string name, Collection<CodeDescription> codes, RepeatDirection repeatDirection, IDictionary<string, object> htmlAttributes, string stateValue = null)
    {
        TagBuilder table = new TagBuilder("table");
        int i = 0;
        if (repeatDirection == RepeatDirection.Horizontal)
        {
            TagBuilder tr = new TagBuilder("tr");
            foreach (var code in codes)
            {
                i++;
                string id = string.Format("{0}_{1}", name, i);
                TagBuilder td = new TagBuilder("td");
                td.InnerHtml = GenerateRadioHtml(name, id, code.Description, code.Code, (stateValue != null && stateValue == code.Code), htmlAttributes);
                tr.InnerHtml+=td.ToString();
            }
            table.InnerHtml = tr.ToString();
        }
        else
        {
            foreach (var code in codes)
            {
                TagBuilder tr = new TagBuilder("tr");
                i++;
                string id = string.Format("{0}_{1}", name, i);
                TagBuilder td = new TagBuilder("td");
                td.InnerHtml = GenerateRadioHtml(name, id, code.Description, code.Code, (stateValue != null && stateValue == code.Code), htmlAttributes);
                tr.InnerHtml = td.ToString();
                table.InnerHtml += tr.ToString();
            }
        }
        return new MvcHtmlString(table.ToString());
    }

    private static string GenerateRadioHtml(string name, string id, string labelText, string value, bool isChecked, IDictionary<string, object> htmlAttributes)
    {
        StringBuilder sb = new StringBuilder();

        TagBuilder label = new TagBuilder("label");
        label.MergeAttribute("for", id);
        label.SetInnerText(labelText);

        TagBuilder input = new TagBuilder("input");
        input.GenerateId(id);
        input.MergeAttribute("name", name);
        input.MergeAttribute("type", "radio");
        input.MergeAttribute("value", value);
        input.MergeAttributes(htmlAttributes);
        if (isChecked)
        {
            input.MergeAttribute("checked", "checked");
        }
        sb.AppendLine(input.ToString());
        sb.AppendLine(label.ToString());
        return sb.ToString();
    }
}

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