c# - MVC Model.IsValid 用于枚举

Question

我有一个网页，其中包含一个由枚举填充的下拉列表。

public enum RegionType
{
    State,
    [System.Xml.Serialization.XmlEnumAttribute("County/District")]
    County_District,
    [System.Xml.Serialization.XmlEnumAttribute("City/Town")]
    City_Town,
    Municipality,
    Village
}

下拉列表其实是通过下面的方式来表达枚举的:

public static List<string> GetRegionTypes()
{
    List<string> theReturn = new List<string>();
    theReturn.Add("");
    foreach (RegionType s in Enum.GetValues(typeof(RegionType))) {
        theReturn.Add(GetXmlEnumValue(s));
    }
    return theReturn;
}

效果很好，下拉列表显示了正确的值和所有内容。问题在于我具有“xmlenum”属性的 2 个值。如果我选择“国家/地区”或“城市/城镇”作为区域类型，则模型的“RegionType”属性无法将其转换为 MVC Controller POST 操作中的相应枚举。我如何让它正确地进行翻译？

Answer 1

您可以定义以下扩展方法，将枚举类型转换为可供 DropDownListFor 助手使用的 SelectList:

public static class EnumExtensions
{
    public static SelectList ToSelectList<TEnum>(this TEnum enumObj)
    {
        var enumType = typeof(TEnum);
        if (enumType.IsGenericType && enumType.GetGenericTypeDefinition() == typeof(Nullable<>))
        {
            enumType = enumType.GetGenericArguments()[0];
        }

        var fields = enumType.GetFields(
            BindingFlags.Static | BindingFlags.GetField | BindingFlags.Public
        );
        var values = Enum.GetValues(enumType).OfType<TEnum>();
        var items =
            from value in values
            from field in fields
            let xmlEnumAttribute = field
                .GetCustomAttributes(
                    typeof(XmlEnumAttribute), true
                )
                .OfType<XmlEnumAttribute>()
                .FirstOrDefault()
            let name = (xmlEnumAttribute != null)
                ? xmlEnumAttribute.Name
                : value.ToString()
            where value.ToString() == field.Name
            select new { Id = value, Name = name };
        return new SelectList(items, "Id", "Name", enumObj);
    }
}

然后就很简单了。你有一个 View 模型:

public class MyViewModel
{
    [Required]
    public RegionType? Region { get; set; }
}

Controller :

public class HomeController : Controller
{
    public ActionResult Index()
    {
        var model = new MyViewModel
        {
            Region = RegionType.City_Town
        };
        return View(model);
    }

    [HttpPost]
    public ActionResult Index(MyViewModel model)
    {
        if (!ModelState.IsValid)
        {
            return View(model);
        }
        return Content("Thanks for choosing " + model.Region.Value.ToString());
    }
}

和一个 View :

@model MyViewModel

@using (Html.BeginForm())
{
    @Html.DropDownListFor(x => x.Region, Model.Region.ToSelectList(), "-- Region --")
    @Html.ValidationMessageFor(x => x.Region)
    <button type="submit">OK</button>
}