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How to get the Display Name Attribute of an Enum member via MVC razor code?

由 人走茶凉 提交于 2019-11-25 23:36:57

问题


I\'ve got a property in my model called \"Promotion\" that its type is a flag enum called \"UserPromotion\". Members of my enum have display attributes set as follows:

[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
}

Now I want to be able to create say a ul in my view to show the selected values of my \"Promotion\" property. This is what I have done so far but the problem is that how can I get the display names here?

<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>

回答1:


UPDATE

First solution was focused on getting display names from enum. Code below should be exact solution for your problem.

You can use this helper class for enums:

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[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();
    }
}

And then you can use it in your view as following:

<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>

Hope it helps! :)




回答2:


One liner - Fluent syntax

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>();
    }
}

Example

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);
    } 
}

Output

Which season is it?
It's summer




回答3:


Building on Aydin's great answer, here's an extension method that doesn't require any type parameters.

using System;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Reflection;

public static class EnumExtensions
{
    public static string GetDisplayName(this Enum enumValue)
    {
        return enumValue.GetType()
                        .GetMember(enumValue.ToString())
                        .First()
                        .GetCustomAttribute<DisplayAttribute>()
                        .GetName();
    }
}

NOTE: GetName() should be used instead of the Name property. This ensures that the localized string will be returned if using the ResourceType attribute property.

Example

To use it, just reference the enum value in your view.

@{
    UserPromotion promo = UserPromotion.SendJobOffersByMail;
}

Promotion: @promo.GetDisplayName()

Output

Promotion: Send Job Offers By Mail




回答4:


Based on Aydin's answer I would suggest a less "duplicatious" implementation (because we could easily get the Type from the Enum value itself, instead of providing it as a parameter 😉:

public static string GetDisplayName(this Enum enumValue)
{
    return enumValue.GetType().GetMember(enumValue.ToString())
                   .First()
                   .GetCustomAttribute<DisplayAttribute>()
                   .Name;
}

EDIT (based upon @Vahagn Nahapetyan's comment)

public static string GetDisplayName(this Enum enumValue)
{
    return enumValue.GetType()?
                    .GetMember(enumValue.ToString())?
                    .First()?
                    .GetCustomAttribute<DisplayAttribute>()?
                    .Name;
}

Now we can use it very clean in this way:

public enum Season 
{
    [Display(Name = "The Autumn")]
    Autumn,

    [Display(Name = "The Weather")]
    Winter,

    [Display(Name = "The Tease")]
    Spring,

    [Display(Name = "The Dream")]
    Summer
}

Season.Summer.GetDisplayName();

Which results in

"The Dream"




回答5:


If you are using MVC 5.1 or upper there is simplier and clearer way: just use data annotation (from System.ComponentModel.DataAnnotations namespace) like below:

public enum Color
{
    [Display(Name = "Dark red")]
    DarkRed,
    [Display(Name = "Very dark red")]
    VeryDarkRed,
    [Display(Name = "Red or just black?")]
    ReallyDarkRed
}

And in view, just put it into proper html helper:

@Html.EnumDropDownListFor(model => model.Color)



回答6:


You could use Type.GetMember Method, then get the attribute info using reflection:

// display attribute of "currentPromotion"

var type = typeof(UserPromotion);
var memberInfo = type.GetMember(currentPromotion.ToString());
var attributes = memberInfo[0].GetCustomAttributes(typeof(DisplayAttribute), false);
var description = ((DisplayAttribute)attributes[0]).Name;

There were a few similar posts here:

Getting attributes of Enum's value

How to make MVC3 DisplayFor show the value of an Enum's Display-Attribute?




回答7:


<ul>
    @foreach (int aPromotion in @Enum.GetValues(typeof(UserPromotion)))
    {
        var currentPromotion = (int)Model.JobSeeker.Promotion;
        if ((currentPromotion & aPromotion) == aPromotion)
        {
        <li>@Html.DisplayFor(e => currentPromotion)</li>
        }
    }
</ul>



回答8:


Building on Todd's great answer which built on Aydin's great answer, here's a generic extension method that doesn't require any type parameters.

/// <summary>
/// Gets human-readable version of enum.
/// </summary>
/// <returns>DisplayAttribute.Name property of given enum.</returns>
public static string GetDisplayName<T>(this T enumValue) where T : IComparable, IFormattable, IConvertible
{
    if (!typeof(T).IsEnum)
        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();
}

I needed this for my project because something like the below code, where not every member of the enum has a DisplayAttribute, does not work with Todd's solution:

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

If this is a complicated solution to a simple problem, please let me know, but this was the fix I used.




回答9:


You need to use a bit of reflection in order to access that attribute:

var type = typeof(UserPromotion);
var member = type.GetMember(Model.JobSeeker.Promotion.ToString());
var attributes = member[0].GetCustomAttributes(typeof(DisplayAttribute), false);
var name = ((DisplayAttribute)attributes[0]).Name;

I recommend wrapping this method in a extension method or perform this in a view model.




回答10:


I'm sorry to do this, but I couldn't use any of the other answers as-is and haven't time to duke it out in the comments.

Uses C# 6 syntax.

static class EnumExtensions
{
    /// returns the localized Name, if a [Display(Name="Localised Name")] attribute is applied to the enum member
    /// returns null if there isnt an attribute
    public static string DisplayNameOrEnumName(this Enum value)
    // => value.DisplayNameOrDefault() ?? value.ToString()
    {
        // More efficient form of ^ based on http://stackoverflow.com/a/17034624/11635
        var enumType = value.GetType();
        var enumMemberName = Enum.GetName(enumType, value);
        return enumType
            .GetEnumMemberAttribute<DisplayAttribute>(enumMemberName)
            ?.GetName() // Potentially localized
            ?? enumMemberName; // Or fall back to the enum name
    }

    /// returns the localized Name, if a [Display] attribute is applied to the enum member
    /// returns null if there is no attribute
    public static string DisplayNameOrDefault(this Enum value) =>
        value.GetEnumMemberAttribute<DisplayAttribute>()?.GetName();

    static TAttribute GetEnumMemberAttribute<TAttribute>(this Enum value) where TAttribute : Attribute =>
        value.GetType().GetEnumMemberAttribute<TAttribute>(value.ToString());

    static TAttribute GetEnumMemberAttribute<TAttribute>(this Type enumType, string enumMemberName) where TAttribute : Attribute =>
        enumType.GetMember(enumMemberName).Single().GetCustomAttribute<TAttribute>();
}



回答11:


With Core 2.1,

public static string GetDisplayName(Enum enumValue)
{
  return enumValue.GetType()?
 .GetMember(enumValue.ToString())?[0]?
 .GetCustomAttribute<DisplayAttribute>()?
 .Name;
}



回答12:


Building further on Aydin's and Todd's answers, here is an extension method that also lets you get the name from a resource file

using AppResources;
using System;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Reflection;
using System.Resources;

public static class EnumExtensions
{
    public static string GetDisplayName(this Enum enumValue)
    {
        var enumMember= enumValue.GetType()
                        .GetMember(enumValue.ToString());

        DisplayAttribute displayAttrib = null;
        if (enumMember.Any()) {
            displayAttrib = enumMember 
                        .First()
                        .GetCustomAttribute<DisplayAttribute>();
        }

        string name = null;
        Type resource = null;

        if (displayAttrib != null)
        {
            name = displayAttrib.Name;
            resource = displayAttrib.ResourceType;
        }

        return String.IsNullOrEmpty(name) ? enumValue.ToString()
            : resource == null ?  name
            : new ResourceManager(resource).GetString(name);
    }
}

and use it like

public enum Season 
{
    [Display(ResourceType = typeof(Resource), Name = Season_Summer")]
    Summer
}



回答13:


combining all edge-cases together from above:

  • enum members with base object members' names (Equals, ToString)
  • optional Display attribute

here is my code:

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());
}



回答14:


For ASP.Net Core 3.0, this worked for me (credit to previous answerers).

My Enum class:

using System;
using System.Linq;
using System.ComponentModel.DataAnnotations;
using System.Reflection;

public class Enums
{
    public enum Duration
    { 
        [Display(Name = "1 Hour")]
        OneHour,
        [Display(Name = "1 Day")]
        OneDay
    }

    // Helper method to display the name of the enum values.
    public static string GetDisplayName(Enum value)
    {
        return value.GetType()?
       .GetMember(value.ToString())?.First()?
       .GetCustomAttribute<DisplayAttribute>()?
       .Name;
    }
}

My View Model Class:

public class MyViewModel
{
    public Duration Duration { get; set; }
}

An example of a razor view displaying a label and a drop-down list. Notice the drop-down list does not require a helper method:

@model IEnumerable<MyViewModel> 

@foreach (var item in Model)
{
    <label asp-for="@item.Duration">@Enums.GetDisplayName(item.Duration)</label>
    <div class="form-group">
        <label asp-for="@item.Duration" class="control-label">Select Duration</label>
        <select asp-for="@item.Duration" class="form-control"
            asp-items="Html.GetEnumSelectList<Enums.Duration>()">
        </select>
    </div>
}



回答15:


Based on previous answers I've created this comfortable helper to support all DisplayAttribute properties in a readable way:

public static class EnumExtensions
    {
        public static DisplayAttributeValues GetDisplayAttributeValues(this Enum enumValue)
        {
            var displayAttribute = enumValue.GetType().GetMember(enumValue.ToString()).First().GetCustomAttribute<DisplayAttribute>();

            return new DisplayAttributeValues(enumValue, displayAttribute);
        }

        public sealed class DisplayAttributeValues
        {
            private readonly Enum enumValue;
            private readonly DisplayAttribute displayAttribute;

            public DisplayAttributeValues(Enum enumValue, DisplayAttribute displayAttribute)
            {
                this.enumValue = enumValue;
                this.displayAttribute = displayAttribute;
            }

            public bool? AutoGenerateField => this.displayAttribute?.GetAutoGenerateField();
            public bool? AutoGenerateFilter => this.displayAttribute?.GetAutoGenerateFilter();
            public int? Order => this.displayAttribute?.GetOrder();
            public string Description => this.displayAttribute != null ? this.displayAttribute.GetDescription() : string.Empty;
            public string GroupName => this.displayAttribute != null ? this.displayAttribute.GetGroupName() : string.Empty;
            public string Name => this.displayAttribute != null ? this.displayAttribute.GetName() : this.enumValue.ToString();
            public string Prompt => this.displayAttribute != null ? this.displayAttribute.GetPrompt() : string.Empty;
            public string ShortName => this.displayAttribute != null ? this.displayAttribute.GetShortName() : this.enumValue.ToString();
        }
    }



回答16:


I tried doing this as an edit but it was rejected; I can't see why.

The above will throw an exception if you call it with an Enum that has a mix of custom attributes and plain items, e.g.

public enum CommentType
{
    All = 1,
    Rent = 2,
    Insurance = 3,
    [Display(Name="Service Charge")]
    ServiceCharge = 4
}

So I've modified the code ever so slightly to check for custom attributes before trying to access them, and use the name if none are found.

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();
    }
}



回答17:


I want to contribute with culture-dependent GetDisplayName enum extension. Hope this will be usefull for anyone googling this answer like me previously:

"standart" way as Aydin Adn and Todd mentioned:

    public static string GetDisplayName(this Enum enumValue)
    {
        return enumValue
            .GetType()
            .GetMember(enumValue.ToString())
            .First()
            .GetCustomAttribute<DisplayAttribute>()
            .GetName();
    }

"Culture-dependent" way:

    public static string GetDisplayName(this Enum enumValue, CultureInfo ci)
    {
        var displayAttr = enumValue
            .GetType()
            .GetMember(enumValue.ToString())
            .First()
            .GetCustomAttribute<DisplayAttribute>();

        var resMan = displayAttr.ResourceType?.GetProperty(@"ResourceManager", BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic).GetValue(null, null) as ResourceManager;

        return resMan?.GetString(displayAttr.Name, ci) ?? displayAttr.GetName();
    }



回答18:


Using MVC5 you could use:

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
}

then if you want to create a dropdown selector you can use:

@Html.EnumDropdownListFor(expression: model => model.PromotionSelector, optionLabel: "Select")


来源：https://stackoverflow.com/questions/13099834/how-to-get-the-display-name-attribute-of-an-enum-member-via-mvc-razor-code

标签
c#
asp.net-mvc
razor
displayattribute
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