Using Generics and enums in C# to create a list of attributes

Question

Good morning. I have the need to create a little helper class, using generics, however my knowledge of generics is very low. So here is what i need. i have defined enums in C#, to have description properties. for example

public enum EnumLineItemErrorCode
{
    [Description("None")]
    None = 0,
    [Description("helpful Desc")]
    MissnigA= 1,
    [Description("another desc")]
    MissingB = 2
}

I also have created helper functions that get he description out of the enums like

public static string GetEnumDescription(Enum value)
{
    FieldInfo fi = value.GetType().GetField(value.ToString());
    DescriptionAttribute[] attributes =
        (DescriptionAttribute[])fi.GetCustomAttributes(typeof(DescriptionAttribute), false);
    return attributes.Length > 0 ? attributes[0].Description : value.ToString();
}

Now if i need the desc i can call the method like the following

EnumerationsHelper.GetEnumDescription(EnumLineItemErrorCode.MissnigA);

However when we want to do bindinds to a datasource i currently do the following for each value on the enum.

dropdownList.Add(new ListItem(EnumerationsHelper.GetEnumDescription(EnumLineItemErrorCode.MissnigA), EnumLineItemErrorCode.MissnigA.ToString()));

But this approach is inflexible as the enum grows in size and also because it does not automatically adds a value to the list if i just add it to the enum.

So my question is.

Can u create a helper method that will return me a list of Description, Value, where description is the enum description and the value is the enum internal value. For example on the code that i have will be used as

object t EnumerationsHelper.GetDescriptionAndValuesAslist(EnumLineItemErrorCode);

and object t is structure of with values <"None",None">,<"MissnigA","helpful Desc">,<"MissingB","another desc">

Thank you in advance.

Answer 1

This will do the job.

private string[] GetEnumDescriptions<T>()
{
    return Enum.GetValues(typeof(T))
               .Cast<Enum>()
               .Select(GetEnumDescription)
               .ToArray();
}

Use case:

var descriptions = GetDescriptions<EnumLineItemErrorCode>();

Note: If T is not of type Enum Enum.GetValues method will throw exception.

Answer 2

这是您正在寻找的： Enum.GetValues

Answer 3

I quickly wrote the following helper method for you

public static IDictionary<string, string> GetEnumBindings<T>()
{
    if (!typeof(Enum).IsAssignableFrom(typeof(T)))
    {
        throw new ArgumentException("The provided type is not an enum");
    }

    var result = new Dictionary<string, string>();
    var fieldNames = Enum.GetNames(typeof (T));

    foreach (var fieldName in fieldNames)
    {
        var fieldAttributes = typeof (T).GetField(fieldName)
                                       .GetCustomAttributes(typeof (DescriptionAttribute), false);

        var description = fieldAttributes.Any()
                              ? ((DescriptionAttribute) fieldAttributes.First()).Description
                              : fieldName;

        result.Add(fieldName, description);
    }

    return result;
}

And use case is:

var bindings = GetEnumBindings<EnumLineItemErrorCode>();
var listItems = bindings.Select(b => new ListItem(b.Value, b.Key));

After that just add listItems to your DropDownList. Good luck!

UPD: Since description is not unique, I modified code a little bit to add field name as a key to the dictionary.