Question

I had an odd problem today when I was trying to serialize an object. The object was generated via ‘Add service reference’ from a web service (svcutil.exe).

The problem was that the below property (agencyId) was not being serialized with the rest of the object. Out of desperation I commented the property below it because it had the ‘XMLIgnoreAttribute’ assigned… after I commented the ignored property, the agencyId field serialized as expected.

Can someone please explain to me why this behavior occurred? Thanks!!

        /// <remarks/>     [System.Xml.Serialization.XmlElementAttribute(Form=System.Xml.Schema.XmlSchemaForm.Unqualified, Order=1)]     public string agencyId     {         get {             return this.agencyIdField;         }         set {             this.agencyIdField = value;             this.RaisePropertyChanged('agencyId');         }     }      /// <remarks/>     [System.Xml.Serialization.XmlIgnoreAttribute()]     public bool agencyIdSpecified     {         get         {             return this.agencyIdFieldSpecified;         }         set         {             this.agencyIdFieldSpecified = value;             this.RaisePropertyChanged('agencyIdSpecified');         }     } 

Answer 1

There is a pattern (for XmlSerializer), that a property Foo will also look for either ‘bool FooSpecified’, or ‘bool ShouldSerializeFoo()’ – and if found, only serialize Foo if this other member returns true. So I assume that agencyIdSpecified had never been set to true? Removing this member would make it always serialize (unless you add a [DefaultValue] or similar).

This type of behaviour is used to model optional values on the occasion that we really need to know whether it was in the original data – i.e. does it have the value 0 because the caller told us that number, or because that is simply the default.

Note that the ‘FooSpecified’ member commonly has [XmlIgnore] so that XmlSerializer knows that it shouldn’t be considered as data for serialization. This isn’t necessary (or legal, in fact) with ‘ShouldSerializeFoo()’, since methods are never serialized.