How to get an IEnumerable<string> of enum values attributes?
I have a StringValue attribute for enums values, so I could attach a description to each value:
public class StringValueAttribute : Attribute
{
public string Value { get; private set; }
public StringValueAttribute(string value)
{
Value = value;
}
}
And that is how I use it:
enum Group
{
[StringValue("Computer Science")]
ComputerScience,
[StringValue("Software Engineering")]
SoftwareEngineering,
// ... additional values follow.
}
I have a method that retrieves the StringValue given the enum value:
public static string GetStringValue(Enum value)
{
Type type = value.GetType();
FieldInfo fieldInfo = type.GetField(type.ToString());
StringValueAttribute[] attributes = fieldInfo.GetCustomAttributes(typeof(StringValueAttribute), false) as StringValueAttribute[];
string stringValue = null;
if (attributes.Length > 0)
{
stringValue = attributes[0].Value;
}
return stringValue;
}
I want to have another method that gets an enum (the enum itself, not a value) and retrieves an IEnumerable using the GetStringValue method. I am not sure how to accomplish that. How could a method like this look like?
Edit: this question is not a duplicate of How to get C# Enum description from value?. I know how to get an enum attribute value, and I actually have a method in the question that does exactly that. My question is how to enumerate all the attributes in an enum.
The most straightforward way to do this is with a generic, though you could always pass in an instance of your specific Enum , get its type, then return the StringValue values for all its values:
public static class EnumExtensions
{
public static IEnumerable<string> GetStringValues<TEnum>() where TEnum : struct, IConvertible, IComparable, IFormattable
{
return Enum.GetValues(typeof(TEnum))
.Cast<Enum>()
.Select(e => e.GetStringValue())
.ToList();
}
public static IEnumerable<string> GetStringValuesOfType(Enum value)
{
return Enum.GetValues(value.GetType())
.Cast<Enum>()
.Select(e => e.GetStringValue())
.ToList();
}
public static string GetStringValue(this Enum value)
{
Type type = value.GetType();
FieldInfo fieldInfo = type.GetField(value.ToString());
StringValueAttribute[] attributes = fieldInfo.GetCustomAttributes(typeof(StringValueAttribute), false) as StringValueAttribute[];
string stringValue = null;
if (attributes.Length > 0)
{
stringValue = attributes[0].Value;
}
return stringValue;
}
}
Notes:
There is no where TEnum : Enum constraint in c#. Restricting TEnum to be struct, IConvertible, IComparable, IFormattable is mostly sufficient.
That being said, there is a cunning trick to apply an enum constraint which is shown in this answer to Enum type constraints in C# by SLaks. (I didn't use it in this answer though since it's really very cunning.)
As noted in @EdPlunkett's comment you need to pass value.ToString() to type.GetField() since you're getting the field corresponding to that specific incoming enum value.
Sample fiddle
这应该工作：
static void Main(string[] args)
{
foreach (var item in GetStringNames<Group>())
{
Console.WriteLine(item);
}
}
public static string GetStringValue(Enum value)
{
Type type = value.GetType();
FieldInfo fieldInfo = type.GetField(value.ToString());
StringValueAttribute[] attributes = fieldInfo.GetCustomAttributes(typeof(StringValueAttribute), false) as StringValueAttribute[];
string stringValue = null;
if (attributes.Length > 0)
{
stringValue = attributes[0].Value;
}
return stringValue;
}
public static IEnumerable<string> GetStringNames<T>()
{
var type = typeof(T);
if (type.IsEnum == false)
{
throw new ArgumentException("T must be an Enum type");
}
var values = type.GetEnumValues();
foreach (var item in values)
{
yield return GetStringValue((Enum)item);
}
}
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