Getting data from property attribute

Question

I have a view model which uses custom attributes such as

public int Id { get; set; }
public string Name { get; set; }
[IsEnumeration(typeof(CaseStatus))]
public string Status { get; set; }

IsEnumeration is a custom attribute which takes an Enumeration superclass as a parameter (actually it takes any type, but that doesn't matter since noone else will be using this)

public class IsEnumerationAttribute : Attribute
{
    public Type Enumeration;
    public IsEnumerationAttribute(Type enumeration)
    {
        Enumeration = enumeration;
    }
}

What I want is to be able to get the type specified for any parameter. Currently my code looks like this:

    public T EnumerationValuesToDisplayNames<T>(T item) where T : new()
    {
        if (LoggedInUser.IsSuper) return item;
        var tProps = typeof (T).GetProperties()
            .Where(prop => Attribute
                 .IsDefined(prop, typeof (IsEnumerationAttribute)));

        foreach (var prop in tProps)
        {
            if (prop.GetValue(item, null) != null)
            {
                /*

    Here I look through all properties with the IsEnumerable attribute.
    I want to do something such as:
                var type = prop.GetAttribute(item, typeof(IsEnumerable));
                var displayName = Enumeration<type>.FromId(prop.GetValue(item, null));
                prop.SetValue(item, displayName);

                */
            }
        }
        return item;
    }

I hope this makes sense, any help would be greatly appreciated, thanks

Just to add, both the Id and DisplayName for Status are string. Ie a status could be id: CNC, display name: Cancelled. All Enumeration<>.FromValue does is converts between this id and the display name — Jordan Wallwork
– Jordan Wallwork, Commented Sep 12, 2011 at 15:13

Bob Vale · Accepted Answer · 2011-09-12 15:40:33Z

Assuming from your post you have a class defined as such:

public class Enumeration<T> {

  public static string FromId(string id) {
    // FromId Implmentation
  }

}

Then you should just need

foreach (var prop in tProps) {  
  var id=prop.GetValue(item, null);
  if (id!=null) {  
    var type = prop.GetCustomAttributes(typeof(EnumerationAttribute>,true).OfType<EnumerationAttribute>().Select(x=>x.Enumeration).First();
    var enumerationType=typeof(Enumeration<>).MakeGenericType(type);
    var fromIdMethod=enumerationType.GetMethod("FromId",BindingFlags.Public|BindingFlags.Static|BindingFlags.InvokeMethod);
    var displayName=fromIdMethod.Invoke(null,new object[] {id});
    prop.SetValue(item, displayName);  
  }  
}

Alternatively you could implement the FromId method directly in the EnumerationAttribute then you could just call it directly like so...

foreach (var prop in tProps) {  
  var id=prop.GetValue(item, null);
  if (id!=null) {  
    var enumAttrib = prop.GetCustomAttributes(typeof(EnumerationAttribute>,true).OfType<EnumerationAttribute>().First();
    var displayName=enumAttrib.FromId((string)id);
    prop.SetValue(item, displayName);  
  }

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