C# – Web Service and System.InvalidOperationException while serializing

csoapweb services

I have the following class which throws an InvalidOperationException when the class is serialized

public class CustomFieldList : CustomField, IList
  {
        public CustomFieldList()
        {
              this.ControlType = Rflex.Framework.MetaData.ControlType.DDL;
        }
        public Type ReferentielType { get; set; }
        public int? CustomCodeTableTypeID { get; set; }
        public CustomCodeTableItem Value { get; set; }
        public override object TheValue { get { return Value; } }
  }

It can't serialize Type which maybe is a normal thing ?

The stack (error translated from French so it's not accurate) :

System.InvalidOperationException: Error while processing XML. —> System.InvalidOperationException: The type Rflex.WebServices.Objects.Reference.CustomCodeTableItem is not recognized. use XmlInclude or SoapInclude attribute to specify types …..
à Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write32_Type(String n, String ns, Type o, Boolean isNullable, Boolean needType)
à Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write33_CustomFieldList(String n, String ns, CustomFieldList o, Boolean isNullable, Boolean needType)
à Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write74_JobDescription(String n, String ns, JobDescription o, Boolean isNullable, Boolean needType)
à Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write77_Offer(String n, String ns, Offer o, Boolean isNullable, Boolean needType)
à Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriter1.Write96_Offer(Object o)
à Microsoft.Xml.Serialization.GeneratedAssembly.OfferSerializer.Serialize(Object objectToSerialize, XmlSerializationWriter writer)
à System.Xml.Serialization.XmlSerializer.Serialize(XmlWriter xmlWriter, Object o, XmlSerializerNamespaces namespaces, String encodingStyle, String id)

I tried with attributes but it doesn't want to work.

Best Answer

You'll need this:

[XmlInclude(typeof(Rflex.WebServices.Objects.Reference.CustomCodeTableItem))]

added to the type that is actually returned from your web service.

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

Actionscript – How to pass “Null” (a real surname!) to a SOAP web service in ActionScript 3

Tracking it down

At first I thought this was a coercion bug where null was getting coerced to "null" and a test of "null" == null was passing. It's not. I was close, but so very, very wrong. Sorry about that!

I've since done lots of fiddling on wonderfl.net and tracing through the code in mx.rpc.xml.*. At line 1795 of XMLEncoder (in the 3.5 source), in setValue, all of the XMLEncoding boils down to

currentChild.appendChild(xmlSpecialCharsFilter(Object(value)));

which is essentially the same as:

currentChild.appendChild("null");

This code, according to my original fiddle, returns an empty XML element. But why?

Cause

According to commenter Justin Mclean on bug report FLEX-33664, the following is the culprit (see last two tests in my fiddle which verify this):

var thisIsNotNull:XML = <root>null</root>;
if(thisIsNotNull == null){
    // always branches here, as (thisIsNotNull == null) strangely returns true
    // despite the fact that thisIsNotNull is a valid instance of type XML
}

When currentChild.appendChild is passed the string "null", it first converts it to a root XML element with text null, and then tests that element against the null literal. This is a weak equality test, so either the XML containing null is coerced to the null type, or the null type is coerced to a root xml element containing the string "null", and the test passes where it arguably should fail. One fix might be to always use strict equality tests when checking XML (or anything, really) for "nullness."

Solution

The only reasonable workaround I can think of, short of fixing this bug in every damn version of ActionScript, is to test fields for "null" and escape them as CDATA values.

CDATA values are the most appropriate way to mutate an entire text value that would otherwise cause encoding/decoding problems. Hex encoding, for instance, is meant for individual characters. CDATA values are preferred when you're escaping the entire text of an element. The biggest reason for this is that it maintains human readability.

Best Answer

Related Solutions

C# – the difference between String and string in C#

This is the style that Microsoft tends to use in their examples.

Actionscript – How to pass “Null” (a real surname!) to a SOAP web service in ActionScript 3

Tracking it down

Cause

Solution

Related Topic