Question

I am currently updating some exising Silverlight code and moving helper classes into a Silverlight 5 library but I am struggling with the change from a HashTable implementation to a IDictionary implementation as shown below.

This functionality allows the enumerations to be attributed allowing the looking up of a string value.

The code compiles but fails on the stringValues.Add(value, attrs[0]); line in the ParseEnumStrings class with the below exception details.

Any idea what I have done wrong in the conversion of the code?

Exception

The value "Today" is not of type "System.Type" and cannot be used in this generic collection.
Parameter name: key.

   at System.ThrowHelper.ThrowWrongKeyTypeArgumentException(Object key, Type targetType)
   at System.Collections.Generic.Dictionary`2.System.Collections.IDictionary.Add(Object key, Object value)
   at Silverlight.Helper.Enums.ParseEnumStrings.GetStringValue(Enum value) in Z:\Perforce\Development\Microsoft .Net\dotNet 4.0\Silverlight 5\Helper\Helper\Enums\ParseEnumStrings.cs:line 25
   at QSmartFaultsByZone.Web.Models.QSmartService.GetRTF(Int32 buID, String zones, ReportTimePeriod time) in Z:\Perforce\Development\Microsoft .Net\dotNet 4.0\Silverlight 5\QSmart Faults By Zone\QSmartFaultsByZone.Web\Models\QSmartService.cs:line 114
   at GetRTF(DomainService , Object[] )
   at System.ServiceModel.DomainServices.Server.ReflectionDomainServiceDescriptionProvider.ReflectionDomainOperationEntry.Invoke(DomainService domainService, Object[] parameters)
   at System.ServiceModel.DomainServices.Server.DomainOperationEntry.Invoke(DomainService domainService, Object[] parameters, Int32& totalCount)
   at System.ServiceModel.DomainServices.Server.DomainService.Query(QueryDescription queryDescription, IEnumerable`1& validationErrors, Int32& totalCount)

Enum

public enum ReportTimePeriod 
{
    [StringValue("Today")]
    Today = 0,
    [StringValue("Twenty Four Hours")]
    TwentyFourHours = 1,
    [StringValue("Week")]
    Week = 2,
    [StringValue("Month")]
    Month = 3
}

String Value Attribute

public class StringValueAttribute : Attribute
{
    private readonly string value;

    public StringValueAttribute(string value)
    {
        this.value = value;
    }

    public string Value
    {
        get { return this.value; }
    }
}

Legacy HashTable class

public class ParseEnumStrings
{
    private static Hashtable _stringValues = new Hashtable();

    public static string GetStringValue(Enum value)
    {
        string output = null;
        Type type = value.GetType();

        //Check first in our cached results...
        if (_stringValues.ContainsKey(value))
            output = (_stringValues[value] as StringValueAttribute).Value;
        else
        {
            //Look for our 'StringValueAttribute' 
            //in the field's custom attributes
            FieldInfo fi = type.GetField(value.ToString());
            StringValueAttribute[] attrs =fi.GetCustomAttributes(typeof(StringValueAttribute),false) as StringValueAttribute[];
            if (attrs.Length > 0)
            {
                _stringValues.Add(value, attrs[0]);
                output = attrs[0].Value;
            }
        }

        return output;
    }

New IDictionary implementation

public class ParseEnumStrings
{
    private static IDictionary stringValues = new Dictionary<Type, StringValueAttribute>();

    public static string GetStringValue(Enum value)
    {
        string result = string.Empty;
        Type type = value.GetType();

        if (stringValues.Contains(value))
            result=(stringValues[value] as StringValueAttribute).Value;
        else
        {
            FieldInfo f = type.GetField(value.ToString());
            StringValueAttribute[] attrs = f.GetCustomAttributes(typeof(StringValueAttribute), false) as StringValueAttribute[];
            if (attrs.Length > 0)
            {
                stringValues.Add(value, attrs[0]);
                result = attrs[0].Value;
            }
        }

        return result;
    }
}

Implementation

return (from rft in qs.spBusinessProductsRFTTodayV2(zones, buID, ParseEnumStrings.GetStringValue(time))
        select new RightFirstTimeReportDto
        {
            Builds=rft.Builds,
            BuildsWithFaults=rft.BuildsWithFaults,
            Name=rft.Name,
            RightFirstTime=rft.RFT,
            ZoneID=rft.ZoneID
        }).ToList();

Answer 1

The problem is, your dictionary’s TKey is System.Type, but you’re expecting to use the values of your enumeration as keys. The dictionary’s type should probably be IDictionary<object, StringValueAttribute>

(Also, you’re using Contains instead of ContainsKey in the second version. Although the documentation does state that IDictionary.Contains should look at the keys, so I’m not entirely sure why that doesn’t do what you expect.)