How to have userfriendly names for enumerations? [

问题:

This question already has an answer here:

• String representation of an Enum 34 answers
• Localizing enum descriptions attributes 8 answers

I have an enumeration like

Enum Complexity
{
  NotSoComplex,
  LittleComplex,
  Complex,
  VeryComplex
}

And I want to use it in a dropdown list, but don't want to see such Camel names in list (looks really odd for users). Instead I would like to have in normal wording, like Not so complex Little complex (etc)

Also, my application is multi-lang and I would like to be able to display those strings localized, and I use a helper, TranslationHelper(string strID) which gives me the localized version for a string id.

I have a working solution, but not very elegant: I create a helper class for the enum, with one member Complexity and ToString() overwritten, like below (code simplified)

public class ComplexityHelper
{
    public ComplexityHelper(Complexity c, string desc)
    { m_complex = c; m_desc=desc; }

    public Complexity Complexity { get { ... } set {...} }
    public override ToString() { return m_desc; }

    //Then a static field like this 

    private static List<Complexity> m_cxList = null;

    // and method that returns the status lists to bind to DataSource of lists
    public static List<ComplexityHelper> GetComplexities() 
    {
        if (m_cxList == null)
        {
           string[] list = TranslationHelper.GetTranslation("item_Complexities").Split(',');
           Array listVal = Enum.GetValues(typeof(Complexities));
           if (list.Length != listVal.Length)
               throw new Exception("Invalid Complexities translations (item_Complexities)");
           m_cxList = new List<Complexity>();
           for (int i = 0; i < list.Length; i++)
           {
             Complexity cx = (ComplexitylistVal.GetValue(i);
             ComplexityHelper ch = new ComplexityHelper(cx, list[i]);
             m_cxList.Add(ch);
           }
        }
        return m_cxList;
    }
}

While workable, I'm not happy with it, since I have to code it similarily for various enums I need to use in picklists.

Does anyone have a suggestion for a simpler or more generic solution?

Thanks Bogdan

回答1:

Basic Friendly names

Use the Description attribute:*

enum MyEnum
{
    [Description("This is black")]
    Black,
    [Description("This is white")]
    White
}

And a handy extension method for enums:

public static string GetDescription(this Enum value)
{
    FieldInfo field = value.GetType().GetField(value.ToString());
    object[] attribs = field.GetCustomAttributes(typeof(DescriptionAttribute), true);
    if(attribs.Length > 0)
    {
        return ((DescriptionAttribute)attribs[0]).Description;
    }
    return string.Empty;
}

Used like so:

MyEnum val = MyEnum.Black;
Console.WriteLine(val.GetDescription()); //writes "This is black"

(Note this doesn't exactly work for bit flags...)

For localization

There is a well-established pattern in .NET for handling multiple languages per string value - use a resource file, and expand the extension method to read from the resource file:

public static string GetDescription(this Enum value)
{
    FieldInfo field = value.GetType().GetField(value.ToString());
    object[] attribs = field.GetCustomAttributes(typeof(DescriptionAttribute), true));
    if(attribs.Length > 0)
    {
        string message = ((DescriptionAttribute)attribs[0]).Description;
        return resourceMgr.GetString(message, CultureInfo.CurrentCulture);
    }
    return string.Empty;
}

Any time we can leverage existing BCL functionality to achieve what we want, that's definitely the first route to explore. This minimizes complexity and uses patterns already familiar to many other developers.

Putting it all together

To get this to bind to a DropDownList, we probably want to track the real enum values in our control and limit the translated, friendly name to visual sugar. We can do so by using an anonymous type and the DataField properties on the list:

<asp:DropDownList ID="myDDL"
                  DataTextField="Description"
                  DataValueField="Value" />

myDDL.DataSource = Enum.GetValues(typeof(MyEnum)).OfType<MyEnum>().Select(
    val => new { Description = val.GetDescription(), Value = val.ToString() });

myDDL.DataBind();

Let's break down that DataSource line:

• First we call Enum.GetValues(typeof(MyEnum)), which gets us a loosely-typed Array of the values
• Next we call OfType<MyEnum>() which converts the array to an IEnumerable<MyEnum>
• Then we call Select() and provide a lambda that projects a new object with two fields, Description and Value.

The DataTextField and DataValueField properties are evaluated reflectively at databind-time, so they will search for fields on DataItem with matching names.

-Note in the main article, the author wrote their own DescriptionAttribute class which is unnecessary, as one already exists in .NET's standard libraries.-

回答2:

The use of attributes as in the other answers is a good way to go, but if you just want to use the text from the values of the enum, the following code will split based on the camel-casing of the value:

public static string GetDescriptionOf(Enum enumType)
{
    Regex capitalLetterMatch = new Regex("\\B[A-Z]", RegexOptions.Compiled);
    return capitalLetterMatch.Replace(enumType.ToString(), " $&");
}

Calling GetDescriptionOf(Complexity.NotSoComplex) will return Not So Complex. This can be used with any enum value.

To make it more useful, you could make it an extension method:

public static string ToFriendlyString(this Enum enumType)
{
    Regex capitalLetterMatch = new Regex("\\B[A-Z]", RegexOptions.Compiled);
    return capitalLetterMatch.Replace(enumType.ToString(), " $&");
}

You cal now call it using Complexity.NotSoComplex.ToFriendlyString() to return Not So Complex.

---

EDIT: just noticed that in your question you mention that you need to localise the text. In that case, I'd use an attribute to contain a key to look up the localised value, but default to the friendly string method as a last resort if the localised text cannot be found. You would define you enums like this:

enum Complexity
{
    [LocalisedEnum("Complexity.NotSoComplex")]
    NotSoComplex,
    [LocalisedEnum("Complexity.LittleComplex")]
    LittleComplex,
    [LocalisedEnum("Complexity.Complex")]
    Complex,
    [LocalisedEnum("Complexity.VeryComplex")]
    VeryComplex
}

You would also need this code:

[AttributeUsage(AttributeTargets.Field, AllowMultiple=false, Inherited=true)]
public class LocalisedEnum : Attribute
{
    public string LocalisationKey{get;set;}

    public LocalisedEnum(string localisationKey)
    {
        LocalisationKey = localisationKey;
    }
}

public static class LocalisedEnumExtensions
{
    public static string ToLocalisedString(this Enum enumType)
    {
        // default value is the ToString();
        string description = enumType.ToString();

        try
        {
            bool done = false;

            MemberInfo[] memberInfo = enumType.GetType().GetMember(enumType.ToString());

            if (memberInfo != null && memberInfo.Length > 0)
            {
                object[] attributes = memberInfo[0].GetCustomAttributes(typeof(LocalisedEnum), false);

                if (attributes != null && attributes.Length > 0)
                {
                    LocalisedEnum descriptionAttribute = attributes[0] as LocalisedEnum;

                    if (description != null && descriptionAttribute != null)
                    {
                        string desc = TranslationHelper.GetTranslation(descriptionAttribute.LocalisationKey);

                        if (desc != null)
                        {
                            description = desc;
                            done = true;
                        }
                    }
                }
            }

            if (!done)
            {
                Regex capitalLetterMatch = new Regex("\\B[A-Z]", RegexOptions.Compiled);
                description = capitalLetterMatch.Replace(enumType.ToString(), " $&");
            }
        }
        catch
        {
            description = enumType.ToString();
        }

        return description;
    }
}

To get the localised descriptions, you would then call:

Complexity.NotSoComplex.ToLocalisedString()

This has several fallback cases:

• if the enum has a LocalisedEnum attribute defined, it will use the key to look up the translated text
• if the enum has a LocalisedEnum attribute defined but no localised text is found, it defaults to using the camel-case split method
• if the enum does not have a LocalisedEnum attribute defined, it will use the camel-case split method
• upon any error, it defaults to the ToString of the enum value

回答3:

I use the following class

    public class EnumUtils
    {
    /// <summary>
    ///     Reads and returns the value of the Description Attribute of an enumeration value.
    /// </summary>
    /// <param name="value">The enumeration value whose Description attribute you wish to have returned.</param>
    /// <returns>The string value portion of the Description attribute.</returns>
    public static string StringValueOf(Enum value)
    {
        FieldInfo fi = value.GetType().GetField(value.ToString());
        DescriptionAttribute[] attributes = (DescriptionAttribute[])fi.GetCustomAttributes(typeof(DescriptionAttribute), false);
        if (attributes.Length > 0)
        {
            return attributes[0].Description;
        }
        else
        {
            return value.ToString();
        }
    }

    /// <summary>
    ///     Returns the Enumeration value that has a given Description attribute.
    /// </summary>
    /// <param name="value">The Description attribute value.</param>
    /// <param name="enumType">The type of enumeration in which to search.</param>
    /// <returns>The enumeration value that matches the Description value provided.</returns>
    /// <exception cref="ArgumentException">Thrown when the specified Description value is not found with in the provided Enumeration Type.</exception>
    public static object EnumValueOf(string value, Type enumType)
    {
        string[] names = Enum.GetNames(enumType);
        foreach (string name in names)
        {
            if (StringValueOf((Enum)Enum.Parse(enumType, name)).Equals(value))
            {
                return Enum.Parse(enumType, name);
            }
        }

        throw new ArgumentException("The string is not a description or value of the specified enum.");
    }

Which reads an attribute called description

public enum PuppyType
{
    [Description("Cute Puppy")]
    CutePuppy = 0,
    [Description("Silly Puppy")]
    SillyPuppy
}

回答4:

Thank you all for all answers. Finally I used a combination from Rex M and adrianbanks, and added my own improvements, to simplify the binding to ComboBox.

The changes were needed because, while working on the code, I realized sometimes I need to be able to exclude one enumeration item from the combo. E.g.

Enum Complexity
{
  // this will be used in filters, 
  // but not in module where I have to assign Complexity to a field
  AllComplexities,  
  NotSoComplex,
  LittleComplex,
  Complex,
  VeryComplex
}

So sometimes I want the picklist to show all but AllComplexities (in add - edit modules) and other time to show all (in filters)

Here's what I did:

1. I created a extension method, that uses Description Attribute as localization lookup key. If Description attribute is missing, I create the lookup localization key as EnumName_ EnumValue. Finally, if translation is missing I just split enum name based on camelcase to separate words as shown by adrianbanks. BTW, TranslationHelper is a wrapper around resourceMgr.GetString(...)

The full code is shown below

public static string GetDescription(this System.Enum value)
{
    string enumID = string.Empty;
    string enumDesc = string.Empty;
    try 
    {         
        // try to lookup Description attribute
        FieldInfo field = value.GetType().GetField(value.ToString());
        object[] attribs = field.GetCustomAttributes(typeof(DescriptionAttribute), true);
        if (attribs.Length > 0)
        {
            enumID = ((DescriptionAttribute)attribs[0]).Description;
            enumDesc = TranslationHelper.GetTranslation(enumID);
        }
        if (string.IsNullOrEmpty(enumID) || TranslationHelper.IsTranslationMissing(enumDesc))
        {
            // try to lookup translation from EnumName_EnumValue
            string[] enumName = value.GetType().ToString().Split('.');
            enumID = string.Format("{0}_{1}", enumName[enumName.Length - 1], value.ToString());
            enumDesc = TranslationHelper.GetTranslation(enumID);
            if (TranslationHelper.IsTranslationMissing(enumDesc))
                enumDesc = string.Empty;
        }

        // try to format CamelCase to proper names
        if (string.IsNullOrEmpty(enumDesc))
        {
            Regex capitalLetterMatch = new Regex("\\B[A-Z]", RegexOptions.Compiled);
            enumDesc = capitalLetterMatch.Replace(value.ToString(), " $&");
        }
    }
    catch (Exception)
    {
        // if any error, fallback to string value
        enumDesc = value.ToString();
    }

    return enumDesc;
}

I created a generic helper class based on Enum, which allow to bind the enum easily to DataSource

public class LocalizableEnum
{
    /// <summary>
    /// Column names exposed by LocalizableEnum
    /// </summary>
    public class ColumnNames
    {
        public const string ID = "EnumValue";
        public const string EntityValue = "EnumDescription";
    }
}

public class LocalizableEnum<T>
{

    private T m_ItemVal;
    private string m_ItemDesc;

    public LocalizableEnum(T id)
    {
        System.Enum idEnum = id as System.Enum;
        if (idEnum == null)
            throw new ArgumentException(string.Format("Type {0} is not enum", id.ToString()));
        else
        {
            m_ItemVal = id;
            m_ItemDesc = idEnum.GetDescription();
        }
    }

    public override string ToString()
    {
        return m_ItemDesc;
    }

    public T EnumValue
    {
        get { return m_ID; }
    }

    public string EnumDescription
    {
        get { return ToString(); }
    }

}

Then I created a generic static method that returns a List>, as below

public static List<LocalizableEnum<T>> GetEnumList<T>(object excludeMember)
{
    List<LocalizableEnum<T>> list =null;
    Array listVal = System.Enum.GetValues(typeof(T));
    if (listVal.Length>0)
    {
        string excludedValStr = string.Empty;
        if (excludeMember != null)
            excludedValStr = ((T)excludeMember).ToString();

        list = new List<LocalizableEnum<T>>();
        for (int i = 0; i < listVal.Length; i++)
        {
            T currentVal = (T)listVal.GetValue(i);
            if (excludedValStr != currentVal.ToString())
            {
                System.Enum enumVal = currentVal as System.Enum;
                LocalizableEnum<T> enumMember = new LocalizableEnum<T>(currentVal);
                list.Add(enumMember);
            }
        }
    }
    return list;
}

and a wrapper to return list with all members

public static List<LocalizableEnum<T>> GetEnumList<T>()
{
        return GetEnumList<T>(null);
}

Now let's put all things together and bind to actual combo:

// in module where we want to show items with all complexities
// or just filter on one complexity

comboComplexity.DisplayMember = LocalizableEnum.ColumnNames.EnumValue;
comboComplexity.ValueMember = LocalizableEnum.ColumnNames.EnumDescription;
comboComplexity.DataSource = EnumHelper.GetEnumList<Complexity>();
comboComplexity.SelectedValue = Complexity.AllComplexities;

// ....
// and here in edit module where we don't want to see "All Complexities"
comboComplexity.DisplayMember = LocalizableEnum.ColumnNames.EnumValue;
comboComplexity.ValueMember = LocalizableEnum.ColumnNames.EnumDescription;
comboComplexity.DataSource = EnumHelper.GetEnumList<Complexity>(Complexity.AllComplexities);
comboComplexity.SelectedValue = Complexity.VeryComplex; // set default value

To read selected the value and use it, I use code as below

Complexity selComplexity = (Complexity)comboComplexity.SelectedValue;