Enum Flags的模型绑定列表

Question

我有一个Enum Flags网格,其中每个记录都是一行复选框,用于确定记录的标志值.这是系统提供的通知列表,用户可以选择(每个)他们希望如何传递的通知:

[Flag]
public enum NotificationDeliveryType
{
  InSystem = 1,
  Email = 2,
  Text = 4
}

我找到了这篇文章,但他正在取回一个标志值,并且他将它绑定在控制器中,就像这样(一周中的几天概念):

[HttpPost]
public ActionResult MyPostedPage(MyModel model)
{
  //I moved the logic for setting this into a helper 
  //because this could be re-used elsewhere.
  model.WeekDays = Enum<DayOfWeek>.ParseToEnumFlag(Request.Form, "WeekDays[]");
  ...
}

我无法找到MVC 3模型绑定器可以处理标志的任何地方.谢谢!

Answer 1

一般来说,我在设计视图模型时避免使用枚举,因为它们不能与ASP.NET MVC的助手和开箱即用的模型绑定器一起使用.它们在您的域模型中非常精细,但对于视图模型,您可以使用其他类型.所以我留下了我的映射层,它负责在我的域模型和视图模型之间来回转换,以担心这些转换.

这就是说,如果出于某种原因你决定在这种情况下使用枚举,你可以滚动自定义模型绑定器:

public class NotificationDeliveryTypeModelBinder : DefaultModelBinder
{
    public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
    {
        var value = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
        if (value != null )
        {
            var rawValues = value.RawValue as string[];
            if (rawValues != null)
            {
                NotificationDeliveryType result;
                if (Enum.TryParse<NotificationDeliveryType>(string.Join(",", rawValues), out result))
                {
                    return result;
                }
            }
        }
        return base.BindModel(controllerContext, bindingContext);
    }
}

将在Application_Start中注册:

ModelBinders.Binders.Add(
    typeof(NotificationDeliveryType), 
    new NotificationDeliveryTypeModelBinder()
);

到现在为止还挺好.现在标准的东西:

查看型号:

[Flags]
public enum NotificationDeliveryType
{
    InSystem = 1,
    Email = 2,
    Text = 4
}

public class MyViewModel
{
    public IEnumerable<NotificationDeliveryType> Notifications { get; set; }
}

控制器:

public class HomeController : Controller
{
    public ActionResult Index()
    {
        var model = new MyViewModel
        {
            Notifications = new[]
            {
                NotificationDeliveryType.Email,
                NotificationDeliveryType.InSystem | NotificationDeliveryType.Text
            }
        };
        return View(model);
    }

    [HttpPost]
    public ActionResult Index(MyViewModel model)
    {
        return View(model);
    }
}

查看(~/Views/Home/Index.cshtml):

@model MyViewModel
@using (Html.BeginForm())
{
    <table>
        <thead>
            <tr>
                <th>Notification</th>
            </tr>
        </thead>
        <tbody>
            @Html.EditorFor(x => x.Notifications)
        </tbody>
    </table>
    <button type="submit">OK</button>
}

NotificationDeliveryType(~/Views/Shared/EditorTemplates/NotificationDeliveryType.cshtml)的自定义编辑器模板:

@model NotificationDeliveryType

<tr>
    <td>
        @foreach (NotificationDeliveryType item in Enum.GetValues(typeof(NotificationDeliveryType)))
        {
            <label for="@ViewData.TemplateInfo.GetFullHtmlFieldId(item.ToString())">@item</label>
            <input type="checkbox" id="@ViewData.TemplateInfo.GetFullHtmlFieldId(item.ToString())" name="@(ViewData.TemplateInfo.GetFullHtmlFieldName(""))" value="@item" @Html.Raw((Model & item) == item ? "checked=\"checked\"" : "") />
        }
    </td>
</tr>

很明显,软件开发人员(在本例中为我)在编辑器模板中编写这样的代码不应该为他的工作感到自豪.我的意思是看!即使我在5分钟前写过这个Razor模板,也无法理解它的作用.

因此,我们在可重用的自定义HTML帮助器中重构此意大利面条代码:

public static class HtmlExtensions
{
    public static IHtmlString CheckBoxesForEnumModel<TModel>(this HtmlHelper<TModel> htmlHelper)
    {
        if (!typeof(TModel).IsEnum)
        {
            throw new ArgumentException("this helper can only be used with enums");
        }
        var sb = new StringBuilder();
        foreach (Enum item in Enum.GetValues(typeof(TModel)))
        {
            var ti = htmlHelper.ViewData.TemplateInfo;
            var id = ti.GetFullHtmlFieldId(item.ToString());
            var name = ti.GetFullHtmlFieldName(string.Empty);
            var label = new TagBuilder("label");
            label.Attributes["for"] = id;
            label.SetInnerText(item.ToString());
            sb.AppendLine(label.ToString());

            var checkbox = new TagBuilder("input");
            checkbox.Attributes["id"] = id;
            checkbox.Attributes["name"] = name;
            checkbox.Attributes["type"] = "checkbox";
            checkbox.Attributes["value"] = item.ToString();
            var model = htmlHelper.ViewData.Model as Enum;
            if (model.HasFlag(item))
            {
                checkbox.Attributes["checked"] = "checked";
            }
            sb.AppendLine(checkbox.ToString());
        }

        return new HtmlString(sb.ToString());
    }
}

我们清理编辑器模板中的混乱:

@model NotificationDeliveryType
<tr>
    <td>
        @Html.CheckBoxesForEnumModel()
    </td>
</tr>

产生表:

现在很明显,如果我们能够为这些复选框提供更友好的标签,那就太好了.例如:

[Flags]
public enum NotificationDeliveryType
{
    [Display(Name = "in da system")]
    InSystem = 1,

    [Display(Name = "@")]
    Email = 2,

    [Display(Name = "txt")]
    Text = 4
}

我们所要做的就是调整我们之前编写的HTML帮助器:

var field = item.GetType().GetField(item.ToString());
var display = field
    .GetCustomAttributes(typeof(DisplayAttribute), true)
    .FirstOrDefault() as DisplayAttribute;
if (display != null)
{
    label.SetInnerText(display.Name);
}
else
{
    label.SetInnerText(item.ToString());
}

这给了我们更好的结果:

Answer 2

Darin的代码很棒,但我在使用MVC4时遇到了一些麻烦.

在创建框的HtmlHelper扩展中,我不断得到模型不是枚举的运行时错误(具体来说,说System.Object).我重新编写代码以获取Lambda表达式并使用ModelMetadata类清除此问题:

public static IHtmlString CheckBoxesForEnumFlagsFor<TModel, TEnum>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TEnum>> expression)
{
    ModelMetadata metadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);
    Type enumModelType = metadata.ModelType;

    // Check to make sure this is an enum.
    if (!enumModelType.IsEnum)
    {
        throw new ArgumentException("This helper can only be used with enums. Type used was: " + enumModelType.FullName.ToString() + ".");
    }

    // Create string for Element.
    var sb = new StringBuilder();
    foreach (Enum item in Enum.GetValues(enumModelType))
    {
        if (Convert.ToInt32(item) != 0)
        {
            var ti = htmlHelper.ViewData.TemplateInfo;
            var id = ti.GetFullHtmlFieldId(item.ToString());
            var name = ti.GetFullHtmlFieldName(string.Empty);
            var label = new TagBuilder("label");
            label.Attributes["for"] = id;
            var field = item.GetType().GetField(item.ToString());

            // Add checkbox.
            var checkbox = new TagBuilder("input");
            checkbox.Attributes["id"] = id;
            checkbox.Attributes["name"] = name;
            checkbox.Attributes["type"] = "checkbox";
            checkbox.Attributes["value"] = item.ToString();
            var model = htmlHelper.ViewData.Model as Enum;
            if (model.HasFlag(item))
            {
                checkbox.Attributes["checked"] = "checked";
            }
            sb.AppendLine(checkbox.ToString());

            // Check to see if DisplayName attribute has been set for item.
            var displayName = field.GetCustomAttributes(typeof(DisplayNameAttribute), true)
                .FirstOrDefault() as DisplayNameAttribute;
            if (displayName != null)
            {
                // Display name specified.  Use it.
                label.SetInnerText(displayName.DisplayName);
            }
            else
            {
                // Check to see if Display attribute has been set for item.
                var display = field.GetCustomAttributes(typeof(DisplayAttribute), true)
                    .FirstOrDefault() as DisplayAttribute;
                if (display != null)
                {
                    label.SetInnerText(display.Name);
                }
                else
                {
                    label.SetInnerText(item.ToString());
                }
            }
            sb.AppendLine(label.ToString());

            // Add line break.
            sb.AppendLine("<br />");
        }                
    }

    return new HtmlString(sb.ToString());
}

我还扩展了模型绑定器,因此它适用于任何通用枚举类型.

public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
    // Fetch value to bind.
    var value = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);
    if (value != null)
    {
        // Get type of value.
        Type valueType = bindingContext.ModelType;

        var rawValues = value.RawValue as string[];
        if (rawValues != null)
        {
            // Create instance of result object.
            var result = (Enum)Activator.CreateInstance(valueType);

            try
            {
                // Parse.
                result = (Enum)Enum.Parse(valueType, string.Join(",", rawValues));
                return result;
            }
            catch
            {
                return base.BindModel(controllerContext, bindingContext);
            }
        }
    }
    return base.BindModel(controllerContext, bindingContext);
}

您仍然需要在Application_Start中注册每个枚举类型,但至少这样就不需要单独的绑定器类.您可以使用以下方式注册:

ModelBinders.Binders.Add(typeof(MyEnumType), new EnumFlagsModelBinder());

我在Github上发布了我的代码:https://github.com/Bitmapped/MvcEnumFlags.

Answer 3

您可以尝试MVC Enum Flags包(可通过nuget获得).它会自动跳过零值枚举选项,这是一个不错的选择.

[以下内容来自文件及其评论; 如果这不适合你,请看那里]

安装后,将以下内容添加到Global.asax.cs\Application_Start:

ModelBinders.Binders.Add(typeof(MyEnumType), new EnumFlagsModelBinder());

然后在视图中,@using MvcEnumFlags顶部和@Html.CheckBoxesForEnumFlagsFor(model => model.MyEnumTypeProperty)实际代码.