传递枚举值作为参数

Question

I am having trouble in passing multiple enum values from the WCF Client.

class Client
{
    static void Main(string[] args)
    {
        ChannelFactory<IWCFService> channelFactor = new ChannelFactory<IWCFService>("HellowWorldServiceEndpoint");
        channelFactor.Open();

        IWCFService proxy = channelFactor.CreateChannel();
        Console.WriteLine(proxy.GetEnumString(EnumComponents.enumVal1)); // -> SUCCEDED HERE (only one Enum value)
        // Console.WriteLine(proxy.GetEnumString(EnumComponents.enumVal1| EnumComponents.enumVal2)); // -> **** FAILS HERE with invalid enum type. *****
        Console.Read();
    }
}

Exception is, There was an error while trying to serialize parameter http://tempuri.org/:components . The InnerException message was 'Enum value 'enumVal1, enumVal2' is invalid for type 'Microsoft.Geospatial.Data.Gateway.ObjectModel.EnumComponents' and cannot be serialized. Ensure that the necessary enum values are present and are marked with EnumMemberAttribute attribute if the type has DataContractAttribute attribute.'. Please see InnerException for more details

FYI, the enum is from a common library that is added as a reference in WCFclient, WCFserver and WCFinterface.

The same woks if it is a normal function call. Is there a possible way to solve this issue?

Answer 1

The only reason for you to send a bunch of | -ed enum values is in a case where the enum symbolizes flags.

WCF supports using enums with DataContract in few cases - one of them is a flags enum .

In a case where your enum has FlagsAttribute decorating it, the serialization is done in the following way:

• Attempt to find an enumeration member (with the EnumMemberAttribute attribute applied) that maps to the numeric value. If found, send a list that contains just that member.
• Attempt to break the numeric value into a sum such that there are enumeration members (each with the EnumMemberAttribute attribute applied) that map to each part of the sum. Send the list of all these members. Note that the greedy algorithm is used to find such a sum, and thus there is no guarantee that such a sum is found even if it is present. To avoid this problem, make sure that the numeric values of the enumeration members are powers of two.
• If the preceding two steps fail, and the numeric value is nonzero, throw a SerializationException. If the numeric value is zero, send the empty list.

Therefore, you need your enum to look like the following:

[DataContract]
[Flags]
enum EnumComponents
{
    [EnumMember]
    enumVal1,

    [EnumMember]
    enumVal2
}

If the enum is from an external source and it doesn't have the FlagsAttribute you will have to break the numeric value into a sum of enumeration members decorated with EnumMemberAttribute yourself.