我在我的模型中有一个属性叫做Promotion，它的类型是一个标志enum叫做UserPromotion。枚举成员的显示属性设置如下:
[Flags]
public enum UserPromotion
{
None = 0x0,
[Display(Name = "Send Job Offers By Mail")]
SendJobOffersByMail = 0x1,
[Display(Name = "Send Job Offers By Sms")]
SendJobOffersBySms = 0x2,
[Display(Name = "Send Other Stuff By Sms")]
SendPromotionalBySms = 0x4,
[Display(Name = "Send Other Stuff By Mail")]
SendPromotionalByMail = 0x8
}
现在我想要能够在我的视图中创建一个ul来显示我的Promotion属性的选定值。这就是我到目前为止所做的但问题是，我如何在这里获得显示名称?
<ul>
@foreach (int aPromotion in @Enum.GetValues(typeof(UserPromotion)))
{
var currentPromotion = (int)Model.JobSeeker.Promotion;
if ((currentPromotion & aPromotion) == aPromotion)
{
<li>Here I don't know how to get the display attribute of "currentPromotion".</li>
}
}
</ul>
如果你使用的是MVC 5.1或更高版本，有一个更简单、更清晰的方法:只使用数据注释(来自System.ComponentModel.DataAnnotations命名空间)，如下所示:
public enum Color
{
[Display(Name = "Dark red")]
DarkRed,
[Display(Name = "Very dark red")]
VeryDarkRed,
[Display(Name = "Red or just black?")]
ReallyDarkRed
}
在视图中，把它放到合适的html helper中:
@Html.EnumDropDownListFor(model => model.Color)
从上面将所有边情况组合在一起:
枚举包含基对象成员名的成员(Equals, ToString)
可选显示属性
这是我的代码:
public enum Enum
{
[Display(Name = "What a weird name!")]
ToString,
Equals
}
public static class EnumHelpers
{
public static string GetDisplayName(this Enum enumValue)
{
var enumType = enumValue.GetType();
return enumType
.GetMember(enumValue.ToString())
.Where(x => x.MemberType == MemberTypes.Field && ((FieldInfo)x).FieldType == enumType)
.First()
.GetCustomAttribute<DisplayAttribute>()?.Name ?? enumValue.ToString();
}
}
void Main()
{
Assert.Equals("What a weird name!", Enum.ToString.GetDisplayName());
Assert.Equals("Equals", Enum.Equals.GetDisplayName());
}
我试着把它作为一个编辑，但它被拒绝了;我不明白为什么。
如果你用一个混合了自定义属性和普通项的Enum调用它，上面的方法会抛出一个异常。
public enum CommentType
{
All = 1,
Rent = 2,
Insurance = 3,
[Display(Name="Service Charge")]
ServiceCharge = 4
}
因此，我稍微修改了代码，以便在尝试访问自定义属性之前检查它们，如果没有找到则使用名称。
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Reflection;
public static class EnumHelper<T>
{
public static IList<T> GetValues(Enum value)
{
var enumValues = new List<T>();
foreach (FieldInfo fi in value.GetType().GetFields(BindingFlags.Static | BindingFlags.Public))
{
enumValues.Add((T)Enum.Parse(value.GetType(), fi.Name, false));
}
return enumValues;
}
public static T Parse(string value)
{
return (T)Enum.Parse(typeof(T), value, true);
}
public static IList<string> GetNames(Enum value)
{
return value.GetType().GetFields(BindingFlags.Static | BindingFlags.Public).Select(fi => fi.Name).ToList();
}
public static IList<string> GetDisplayValues(Enum value)
{
return GetNames(value).Select(obj => GetDisplayValue(Parse(obj))).ToList();
}
private static string lookupResource(Type resourceManagerProvider, string resourceKey)
{
foreach (PropertyInfo staticProperty in resourceManagerProvider.GetProperties(BindingFlags.Static | BindingFlags.NonPublic | BindingFlags.Public))
{
if (staticProperty.PropertyType == typeof(System.Resources.ResourceManager))
{
System.Resources.ResourceManager resourceManager = (System.Resources.ResourceManager)staticProperty.GetValue(null, null);
return resourceManager.GetString(resourceKey);
}
}
return resourceKey; // Fallback with the key name
}
public static string GetDisplayValue(T value)
{
var fieldInfo = value.GetType().GetField(value.ToString());
var descriptionAttributes = fieldInfo.GetCustomAttributes(
typeof(DisplayAttribute), false) as DisplayAttribute[];
if (descriptionAttributes.Any() && descriptionAttributes[0].ResourceType != null)
return lookupResource(descriptionAttributes[0].ResourceType, descriptionAttributes[0].Name);
if (descriptionAttributes == null) return string.Empty;
return (descriptionAttributes.Length > 0) ? descriptionAttributes[0].Name : value.ToString();
}
}
基于Todd的答案，建立在Aydin的答案之上，这是一个不需要任何类型参数的泛型扩展方法。
/// <summary>
/// Gets human-readable version of enum.
/// </summary>
/// <returns>effective DisplayAttribute.Name of given enum.</returns>
public static string GetDisplayName<T>(this T enumValue) where T : IComparable, IFormattable, IConvertible // C# 7.3+: where T : struct, Enum
{
if (!typeof(T).IsEnum) // Not needed in C# 7.3+ with above updated constraint
throw new ArgumentException("Argument must be of type Enum");
DisplayAttribute displayAttribute = enumValue.GetType()
.GetMember(enumValue.ToString())
.First()
.GetCustomAttribute<DisplayAttribute>();
string displayName = displayAttribute?.GetName();
return displayName ?? enumValue.ToString();
}
我需要这个为我的项目，因为像下面的代码，其中不是每个成员的enum有一个DisplayAttribute，抛出一个异常与Todd的解决方案:
public class MyClass
{
public enum MyEnum
{
[Display(Name="ONE")]
One,
// No DisplayAttribute
Two
}
public void UseMyEnum()
{
MyEnum foo = MyEnum.One;
MyEnum bar = MyEnum.Two;
Console.WriteLine(foo.GetDisplayName());
Console.WriteLine(bar.GetDisplayName());
}
}
// Output:
//
// ONE
// Two
如果这是一个简单问题的复杂解决方案，请让我知道，但这是我使用的修复。
更新
第一个解决方案侧重于从enum中获取显示名称。下面的代码应该是您的问题的确切解决方案。
你可以为枚举使用这个helper类:
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Reflection;
public static class EnumHelper<T>
where T : struct, Enum // This constraint requires C# 7.3 or later.
{
public static IList<T> GetValues(Enum value)
{
var enumValues = new List<T>();
foreach (FieldInfo fi in value.GetType().GetFields(BindingFlags.Static | BindingFlags.Public))
{
enumValues.Add((T)Enum.Parse(value.GetType(), fi.Name, false));
}
return enumValues;
}
public static T Parse(string value)
{
return (T)Enum.Parse(typeof(T), value, true);
}
public static IList<string> GetNames(Enum value)
{
return value.GetType().GetFields(BindingFlags.Static | BindingFlags.Public).Select(fi => fi.Name).ToList();
}
public static IList<string> GetDisplayValues(Enum value)
{
return GetNames(value).Select(obj => GetDisplayValue(Parse(obj))).ToList();
}
private static string lookupResource(Type resourceManagerProvider, string resourceKey)
{
var resourceKeyProperty = resourceManagerProvider.GetProperty(resourceKey,
BindingFlags.Static | BindingFlags.Public, null, typeof(string),
new Type[0], null);
if (resourceKeyProperty != null)
{
return (string)resourceKeyProperty.GetMethod.Invoke(null, null);
}
return resourceKey; // Fallback with the key name
}
public static string GetDisplayValue(T value)
{
var fieldInfo = value.GetType().GetField(value.ToString());
var descriptionAttributes = fieldInfo.GetCustomAttributes(
typeof(DisplayAttribute), false) as DisplayAttribute[];
if (descriptionAttributes[0].ResourceType != null)
return lookupResource(descriptionAttributes[0].ResourceType, descriptionAttributes[0].Name);
if (descriptionAttributes == null) return string.Empty;
return (descriptionAttributes.Length > 0) ? descriptionAttributes[0].Name : value.ToString();
}
}
然后你可以在视图中使用它，如下所示:
<ul>
@foreach (var value in @EnumHelper<UserPromotion>.GetValues(UserPromotion.None))
{
if (value == Model.JobSeeker.Promotion)
{
var description = EnumHelper<UserPromotion>.GetDisplayValue(value);
<li>@Html.DisplayFor(e => description )</li>
}
}
</ul>
一行-流畅的语法
public static class Extensions
{
/// <summary>
/// A generic extension method that aids in reflecting
/// and retrieving any attribute that is applied to an `Enum`.
/// </summary>
public static TAttribute GetAttribute<TAttribute>(this Enum enumValue)
where TAttribute : Attribute
{
return enumValue.GetType()
.GetMember(enumValue.ToString())
.First()
.GetCustomAttribute<TAttribute>();
}
}
例子
public enum Season
{
[Display(Name = "It's autumn")]
Autumn,
[Display(Name = "It's winter")]
Winter,
[Display(Name = "It's spring")]
Spring,
[Display(Name = "It's summer")]
Summer
}
public class Foo
{
public Season Season = Season.Summer;
public void DisplayName()
{
var seasonDisplayName = Season.GetAttribute<DisplayAttribute>();
Console.WriteLine("Which season is it?");
Console.WriteLine (seasonDisplayName.Name);
}
}
输出
现在是哪个季节?
现在是夏天
