InvalidCastExce ption upon serializing IXmlSerializabl e class

[mattoc]

Happy new year to all.

I have a strange error that I've been trying for a while now to
fathom..

Basically I have a hierarchy of state classes that I need to serialize
to XML. Some of them can contain Exceptions, so I've decided to
implement IXmlSerializabl e to get round the fact that Exception is not
serializable.

Here's the implementation code from the (abstract) superclass:

#region IXmlSerializabl e Members

public void WriteXml(System .Xml.XmlWriter writer)
{
writer.WriteAtt ributeString(Xm lNamespaces.Xml SchemaInstance. Prefix,
"type", XmlNamespaces.X mlSchemaInstanc e.Uri.ToString( ),
this.GetType(). Name);
WriteAdditional ContentXml(writ er);
}

public System.Xml.Sche ma.XmlSchema GetSchema()
{

XmlSchema schema = new XmlSchema();
schema.Id = this.GetType(). FullName;
schema.TargetNa mespace = XmlNamespaces.S ervice.Uri.ToSt ring();

schema.Namespac es.Add(XmlNames paces.Service.P refix,
XmlNamespaces.S ervice.Uri.ToSt ring());
schema.Namespac es.Add(XmlNames paces.XmlSchema Instance.Prefix ,
XmlNamespaces.X mlSchemaInstanc e.Uri.ToString( ));

XmlSchemaComple xType state = new XmlSchemaComple xType();
state.Name = this.GetType(). Name;
schema.Items.Ad d(state);

XmlSchemaSequen ce sequence = new XmlSchemaSequen ce();
sequence.MinOcc urs = 0;
sequence.MaxOcc urs = 1;

AddSchemaConten t(schema, sequence);

if (sequence.Items .Count > 0)
{
state.Particle = sequence;
}

schema.Compile( new ValidationEvent Handler(schemaV alidationHandle r));

return schema;
}

public virtual void ReadXml(System. Xml.XmlReader reader)
{
}

protected virtual void WriteAdditional ContentXml(XmlW riter writer)
{
}

protected virtual void AddSchemaConten t(XmlSchema schema,
XmlSchemaSequen ce parentSequence)
{
}

private void schemaValidatio nHandler(object sender,
ValidationEvent Args args)
{
Trace.WriteLine (args.Message);
Debug.Fail(args .Message + ":" + Environment.New Line +
Environment.New Line + args.Exception. ToString() + Environment.New Line +
Environment.New Line);
}

#endregion

The problem is this. I can (de)serialize whichever type is specified as
the first argument in the XmlSerializer constructor. However, attempts
to serialize any types that are specified in the additional types
argument fail with an InvalidOperatio nException ("There was an error
generating the XML document"), the inner exception of which is an
InvalidCastExce ption ("Specified cast is not valid"), and the stack
trace of which is:

at System.Xml.Seri alization.XmlSe rializer.Serial ize(XmlWriter
xmlWriter, Object o, XmlSerializerNa mespaces namespaces, String
encodingStyle)
at System.Xml.Seri alization.XmlSe rializer.Serial ize(XmlWriter
xmlWriter, Object o)
at
Limit.Company.L ossAdjustment.T ests.State.Stat esTest.serializ e(FeeState
state, XmlSerializer serializer) in
q:\projects\lim it\limit.compan y.lossadjustmen t.tests\state\s tatestest.cs:li ne
131
at
Limit.Company.L ossAdjustment.T ests.State.Stat esTest.XmlSeria lizeErrorState( )
in
q:\projects\lim it\limit.compan y.lossadjustmen t.tests\state\s tatestest.cs:li ne
71
--InvalidOperatio nException
at
Microsoft.Xml.S erialization.Ge neratedAssembly .XmlSerializati onWriter1.Write 1_State(Object
o)

Furthermore, if I explicitly create XML that matches the schema of one
of the additional types, it deserializes, but to the type that was
specified as the FIRST argument of the XmlSerializer constructor. I
guess this means that I have problems with my schemas somewhere, but
I'm at a loss as to how to fix them.

Many thanks in advance,

Matt

[mattoc]

okay - i have figured out what the problem is, and it is nothing to do
with the IXmlSerializabl e interface.

basically, I was trying to use the XmlSerializer in a manner whereby I
would specify that the object I was passing it was any of types A, B, C
or D. it can't handle this. you must specify the type you are passing
it to serialize and then only ever pass it this type. this main type
can contain the other types as part of an object graph, but that's as
far as it goes.

why does it need to know the type you're passing it anyway? surely that
it is marked serializable is enough..
ma****@tiscali. co.uk wrote:

Happy new year to all.

I have a strange error that I've been trying for a while now to
fathom..

Basically I have a hierarchy of state classes that I need to serialize to XML. Some of them can contain Exceptions, so I've decided to
implement IXmlSerializabl e to get round the fact that Exception is not serializable.

Here's the implementation code from the (abstract) superclass:

#region IXmlSerializabl e Members

public void WriteXml(System .Xml.XmlWriter writer)
{
writer.WriteAtt ributeString(Xm lNamespaces.Xml SchemaInstance. Prefix,
"type", XmlNamespaces.X mlSchemaInstanc e.Uri.ToString( ),
this.GetType(). Name);
WriteAdditional ContentXml(writ er);
}

public System.Xml.Sche ma.XmlSchema GetSchema()
{

XmlSchema schema = new XmlSchema();
schema.Id = this.GetType(). FullName;
schema.TargetNa mespace = XmlNamespaces.S ervice.Uri.ToSt ring();

schema.Namespac es.Add(XmlNames paces.Service.P refix,
XmlNamespaces.S ervice.Uri.ToSt ring());
schema.Namespac es.Add(XmlNames paces.XmlSchema Instance.Prefix ,
XmlNamespaces.X mlSchemaInstanc e.Uri.ToString( ));

XmlSchemaComple xType state = new XmlSchemaComple xType();
state.Name = this.GetType(). Name;
schema.Items.Ad d(state);

XmlSchemaSequen ce sequence = new XmlSchemaSequen ce();
sequence.MinOcc urs = 0;
sequence.MaxOcc urs = 1;

AddSchemaConten t(schema, sequence);

if (sequence.Items .Count > 0)
{
state.Particle = sequence;
}

schema.Compile( new ValidationEvent Handler(schemaV alidationHandle r));

return schema;
}

public virtual void ReadXml(System. Xml.XmlReader reader)
{
}

protected virtual void WriteAdditional ContentXml(XmlW riter writer)
{
}

protected virtual void AddSchemaConten t(XmlSchema schema,
XmlSchemaSequen ce parentSequence)
{
}

private void schemaValidatio nHandler(object sender,
ValidationEvent Args args)
{
Trace.WriteLine (args.Message);
Debug.Fail(args .Message + ":" + Environment.New Line +
Environment.New Line + args.Exception. ToString() + Environment.New Line + Environment.New Line);
}

#endregion

The problem is this. I can (de)serialize whichever type is specified as the first argument in the XmlSerializer constructor. However, attempts to serialize any types that are specified in the additional types
argument fail with an InvalidOperatio nException ("There was an error
generating the XML document"), the inner exception of which is an
InvalidCastExce ption ("Specified cast is not valid"), and the stack
trace of which is:

at System.Xml.Seri alization.XmlSe rializer.Serial ize(XmlWriter
xmlWriter, Object o, XmlSerializerNa mespaces namespaces, String
encodingStyle)
at System.Xml.Seri alization.XmlSe rializer.Serial ize(XmlWriter
xmlWriter, Object o)
at
Limit.Company.L ossAdjustment.T ests.State.Stat esTest.serializ e(FeeState state, XmlSerializer serializer) in
q:\projects\lim it\limit.compan y.lossadjustmen t.tests\state\s tatestest.cs:li ne 131
at
Limit.Company.L ossAdjustment.T ests.State.Stat esTest.XmlSeria lizeErrorState( ) in
q:\projects\lim it\limit.compan y.lossadjustmen t.tests\state\s tatestest.cs:li ne 71
--InvalidOperatio nException
at
Microsoft.Xml.S erialization.Ge neratedAssembly .XmlSerializati onWriter1.Write 1_State(Object o)

Furthermore, if I explicitly create XML that matches the schema of one of the additional types, it deserializes, but to the type that was
specified as the FIRST argument of the XmlSerializer constructor. I
guess this means that I have problems with my schemas somewhere, but
I'm at a loss as to how to fix them.

Many thanks in advance,

Matt