Question

我有一个Html Helper，可以将Enum转换为SelectList，如下所示：

public static HtmlString EnumSelectListFor<TModel, TProperty>(
    this HtmlHelper<TModel> htmlHelper,
    Expression<Func<TModel, TProperty>> forExpression,
    object htmlAttributes,
    bool blankFirstLine) where TModel : class where TProperty : struct
{
    //MS, it its infinite wisdom, does not allow enums as a generic constraint, so we have to check here.
    if (!typeof(TProperty).IsEnum) throw new ArgumentException("This helper method requires the specified model property to be an enum type.");

    //initialize values
    var metaData = ModelMetadata.FromLambdaExpression(forExpression, htmlHelper.ViewData);
    var propertyName = metaData.PropertyName;
    var propertyValue = htmlHelper.ViewData.Eval(propertyName).ToStringOrEmpty();

    //build the select tag
    var returnText = string.Format("<select id=\"{0}\" name=\"{0}\"", HttpUtility.HtmlEncode(propertyName));
    if (htmlAttributes != null)
    {
        foreach (var kvp in htmlAttributes.GetType().GetProperties()
            .ToDictionary(p => p.Name, p => p.GetValue(htmlAttributes, null)))
        {
            returnText += string.Format(" {0}=\"{1}\"", HttpUtility.HtmlEncode(kvp.Key),
                HttpUtility.HtmlEncode(kvp.Value.ToStringOrEmpty()));
        }
    }
    returnText += ">\n";

    if (blankFirstLine)
    {
        returnText += "<option value=\"\"></option>";
    }

    //build the options tags
    foreach (var enumName in Enum.GetNames(typeof(TProperty)))
    {
        var idValue = ((int)Enum.Parse(typeof(TProperty), enumName, true)).ToString();
        var displayValue = enumName;
        var titleValue = string.Empty;
        returnText += string.Format("<option value=\"{0}\" title=\"{1}\"",
            HttpUtility.HtmlEncode(idValue), HttpUtility.HtmlEncode(titleValue));
        if (enumName == propertyValue)
        {
            returnText += " selected=\"selected\"";
        }
        returnText += string.Format(">{0}</option>\n", HttpUtility.HtmlEncode(displayValue));
    }

    //close the select tag
    returnText += "</select>";
    return new HtmlString(returnText);
}

我遇到的问题是，Enums的名称中不能有空格，所以如果你有一个单词枚举值以外的东西，你可以得到一些丑陋的选择列表，如下所示：

public enum EmployeeTypes
{
    FullTime = 1,
    PartTime,
    Vendor,
    Contractor
}

现在，我有了一个好主意，“我知道！我将使用DataAnnotations！”所以我让我的枚举看起来像这样：

public enum EmployeeTypes
{
    [Display(Name = "Full Time")]
    FullTime = 1,
    [Display(Name = "Part Time")]
    PartTime,
    [Display(Name = "Vendor")]
    Vendor,
    [Display(Name = "Contractor")]
    Contractor
}

...但现在我正在摸不着如何在我的帮助类中访问这些属性。有人可以让我继续这个吗？

Answer 1

您可以使用循环中的反射从枚举字段中读取DisplayAttribute：

foreach (var enumName in Enum.GetNames(typeof(TProperty)))
{
    var idValue = ((int)Enum.Parse(typeof(TProperty), enumName, true)).ToString();
    var displayValue = enumName;

    // get the corresponding enum field using reflection
    var field = typeof(TProperty).GetField(enumName);
    var display = ((DisplayAttribute[])field.GetCustomAttributes(typeof(DisplayAttribute), false)).FirstOrDefault();
    if (display != null)
    {
        // The enum field is decorated with the DisplayAttribute =>
        // use its value
        displayValue = display.Name;
    }

    var titleValue = string.Empty;
    returnText += string.Format("<option value=\"{0}\" title=\"{1}\"",
        HttpUtility.HtmlEncode(idValue), HttpUtility.HtmlEncode(titleValue));
    if (enumName == propertyValue)
    {
        returnText += " selected=\"selected\"";
    }
    returnText += string.Format(">{0}</option>\n", HttpUtility.HtmlEncode(displayValue));
}

Answer 2

我一直都喜欢为Enum类创建一个扩展方法来读取Description属性，并在你拥有的任何枚举上调用ToDescription（）。这样的事情。

public static class EnumExtensions
{
    public static String ToDescription(this Enum value)
    {
        FieldInfo field = value.GetType().GetField(value.ToString());
        DescriptionAttribute attribute = Attribute.GetCustomAttribute(field, typeof(DescriptionAttribute)) as DescriptionAttribute;
        return attribute == null ? value.ToString() : attribute.Description;
    }   
}

MVC3枚举选择列表，使用显示注释

2 个答案: