Re: Enums and text descriptions - C# Discussion Boards

6-May-08 3:41

I have a series of fairly large enums, and each value within them has a free text equivalent.

Within my code, I need to get the free text for a given enum value. Currently I am using a fairly traditional method of doing this, i.e. a switch/case on the enum value which obtains the text description.

However this is proving to be a pain to maintain, so does anybody know of a way of adding the free text as an attribute of the enum. For example

public enum MyEnum
{
  [Description("This Wibbles")]
  Value1,
  [Description("This Wobbles")]
  Value2,
  [Description("Ding Dong")]
  Value3
}

CPallini6-May-08 3:48

CPallini

6-May-08 3:48

See here [^].
Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

J4amieC6-May-08 3:49

J4amieC

6-May-08 3:49

The description attribute is exactly what I personally use for this, with a simple helper method to obtain the description from the enum item:

<code>public static class EnumHelper
{
    public static string GetDescription(System.Enum enumValue)
    {
        FieldInfo fi = enumValue.GetType().GetField(enumValue.ToString());
        object[] descAttribs = fi.GetCustomAttributes(typeof(DescriptionAttribute), true);
        if (descAttribs.Length == 0)
            return null;
        return ((DescriptionAttribute)descAttribs[0]).Description;
    }
}</code>

Usage:

string description = EnumHelper.GetDescription(MyEnum.Value1);

Hope that helps.

MrEyes6-May-08 4:13

6-May-08 4:13

Thanks alot, that works perfectly

Out of curiosity, is it possible to add object type attributes?

for example

public enum EnumAlpha
{
  value1,
  value2
}

public enum EnumBeta
{
  [ObjectDescription(EnumAlpha.value1)]
  value1,
  [ObjectDescription(EnumAlpha.value2)]
  value2,
}

J4amieC6-May-08 4:17

J4amieC

6-May-08 4:17

I dont see what you're trying to achieve, but the answer is yes, you can define your own attributes and markup your code with those attributes.

MrEyes6-May-08 5:01

6-May-08 5:01

Well to cut a very long story short I am currently in the throws of creating an XML data transformation library. Unfortunately for me neither XML structure can be schema'd and these are also out of my control and cannot be change.

To get around this I have created a series of enums for the 100's of different keys these items contain, so now I am trying to create mapping data from one to the other.

It could be done with switch/case statements, however this is messy and will be complicated to maintain. So I am attempting to use attributes on the input enums to easily convert these to the output format.

So for example each data structure contains the concept of Address Type, e.g.

public enum OutputAddressType
{
  [Description("ResidentialAddress")]
  Residential,
  [Description("CommercialAddress")]
  Commericial,
  [Description("UnknownAddress")]
  Unknown,
  
}

public enum InputAddressType
{
  [Description("ADR001")]
  Home,
  [Description("ADR002")]
  HomeSecondary,
  [Description("ADR003")]
  Business
}

Now as I iterate through the input data object address values, I currently have a switch case that looks something like this:

switch(input.AddressType)
{
  case InputAddressType.Home:
   this.output.AddressType = OutputAddressType.ResidentialAddress;
  break;
  case InputAddressType.HomeSecondary:
   this.output.AddressType = OutputAddressType.Unknown;
  break;
  case InputAddressType.Business:
   this.output.AddressType = OutputAddressType.CommercialAddress;
  break;
}

It would be great if I could do something like this to the input enum:

public enum InputAddressType
{
  [ObjectDescription(InputAddressType.ResidentialAddress)]
  [Description("ADR001")]
  Home,
  [ObjectDescription(InputAddressType.Unknown)]
  [Description("ADR002")]
  HomeSecondary,
  [ObjectDescription(InputAddressType.CommercialAddress)]
  [Description("ADR003")]
  Business
}

The example above is a simple example, however if you imagine that there are over 200 of these enums, each having anywhere from 2 to 200 values you can see why having loads of switch/cases is unmaintainable. Also in the example there is a direct 1 to 1 map from input to output, however in the real world this is a rarity.

PIEBALDconsult6-May-08 5:34

6-May-08 5:34

Will XSLT work?

MrEyes6-May-08 5:50

6-May-08 5:50

Initially I did consider XSLT, however the input XML is a rather interesting example of XML usage, so creating the XSL transform would have been extremely convoluted.

As an example the input XML is entirely attribute based and attribute values and presence depend on the value and presence of other attributes. So for example these two samples represent two different people (customer, staff)

PIEBALDconsult6-May-08 5:28

6-May-08 5:28

There are limitations on what types of values may be passed to attributes.

Generally, only strings and numerics. Even enum values have to be cast to their underlying type (int, short, etc.).

PIEBALDconsult6-May-08 5:30

6-May-08 5:30

But you're using Reflection on each call which is very slow, better to read them once and cache the results (after all the values aren't changing).

J4amieC6-May-08 6:03

J4amieC

6-May-08 6:03

erm.... ok. Feel free to provide a sample that reads Description attributes without the use of Reflection.

And I mean, come on, how slow is this method on the larger scheme of things? An extra 2 milliseconds? I dont think my users will mind.

PIEBALDconsult6-May-08 12:31

6-May-08 12:31

J4amieC wrote:
An extra 2 milliseconds?

Obviously you haven't read this[^] yet.

PIEBALDconsult6-May-08 5:31