XML Serialization of complex types as XML attributes

[Paulo Morgado [MVP]]

Hi all

..NET Framework 1.1

I have created several types that are serailized to XML as strings. Someting
like this:

public struct MyInt32 : IXmlSerializabl e
{
int value;

public MyInt32(int value)
{
this.value = value;
}

public static implicit operator Int32(MyInt32 value)
{
return value.value;
}

public static implicit operator MyInt32(Int32 value)
{
return new MyInt32(value);
}

public static MyInt32 Parse(string str)
{
return int.Parse(str);
}

public static bool TryParse(string str, out MyInt32 value)
{
try
{
value = int.Parse(str);
return true;
}
catch
{
value = 0;
return false;
}
}

XmlSchema IXmlSerializabl e.GetSchema()
{
return null;
}

void IXmlSerializabl e.WriteXml(XmlW riter writer)
{
writer.WriteStr ing(XmlConvert. ToString(this.v alue));
}

void IXmlSerializabl e.ReadXml(XmlRe ader reader)
{
this.value = XmlConvert.ToIn t32(reader.Read String());
}

}

The XML serialization as a XML element works without any problems:

class MyClass
{
[XmlElement("v")]
public MyInt32 myValue;
}

But when I mark myValue with the XmlAttributeAtt ribute:

class MyClass
{
[XmlAttribute("v ")]
public MyInt32 myValue;
}

I get:

System.InvalidO perationExcepti on: There was an error reflecting type
'ConsoleApplica tion.DTO'. ---> System.InvalidO perationExcepti on: There was an
error reflecting field 'v'. ---> System.InvalidO perationExcepti on: Cannot
serialize member 'v'. XmlAttribute/XmlText cannot be used to encode complex
types.
at
System.Xml.Seri alization.XmlRe flectionImporte r.ImportAccesso rMapping(Member Mapping
accessor, FieldModel model, XmlAttributes a, String ns, Type
choiceIdentifie rType)
at
System.Xml.Seri alization.XmlRe flectionImporte r.ImportFieldMa pping(StructMod el
parent, FieldModel model, XmlAttributes a, String ns)
at
System.Xml.Seri alization.XmlRe flectionImporte r.ImportStructL ikeMapping(Stru ctModel model, String ns)
--- End of inner exception stack trace ---
at
System.Xml.Seri alization.XmlRe flectionImporte r.ImportStructL ikeMapping(Stru ctModel model, String ns)
at
System.Xml.Seri alization.XmlRe flectionImporte r.ImportTypeMap ping(TypeModel
model, String ns, ImportContext context, String dataType, Boolean repeats)
--- End of inner exception stack trace ---
at
System.Xml.Seri alization.XmlRe flectionImporte r.ImportTypeMap ping(TypeModel
model, String ns, ImportContext context, String dataType, Boolean repeats)
at System.Xml.Seri alization.XmlRe flectionImporte r.ImportElement (TypeModel
model, XmlRootAttribut e root, String defaultNamespac e)
at System.Xml.Seri alization.XmlRe flectionImporte r.ImportTypeMap ping(Type
type, XmlRootAttribut e root, String defaultNamespac e)
at System.Xml.Seri alization.XmlRe flectionImporte r.ImportTypeMap ping(Type
type)
at System.Xml.Seri alization.XmlSe rializer..ctor( Type type, String
defaultNamespac e)
at System.Xml.Seri alization.XmlSe rializer..ctor( Type type)
at ConsoleApplicat ion.Program.Mai n()

How can I serialize MyType as a XML attribute?

--
Paulo Morgado

[Chris Lovett]

The XmlSerializer doesn't know that your IXmlSerializabl e just calls
WriteString. What if you called WriteElementStr ing instead? So the right
way to do this is expose a string Property

[XmlIgnore]
public MyInt32 MyValue;

[XmlAttribute("v ")]
public string myValue {
get { return MyValue.ToStrin g(); }
set { MyValue = MyInt32.Parse(v alue); }
}

"Paulo Morgado [MVP]" <pa***********@ community.nospa m> wrote in message
news:69******** *************** ***********@mic rosoft.com...

Hi all

.NET Framework 1.1

I have created several types that are serailized to XML as strings.
Someting
like this:

public struct MyInt32 : IXmlSerializabl e
{
int value;

public MyInt32(int value)
{
this.value = value;
}

public static implicit operator Int32(MyInt32 value)
{
return value.value;
}

public static implicit operator MyInt32(Int32 value)
{
return new MyInt32(value);
}

public static MyInt32 Parse(string str)
{
return int.Parse(str);
}

public static bool TryParse(string str, out MyInt32 value)
{
try
{
value = int.Parse(str);
return true;
}
catch
{
value = 0;
return false;
}
}

XmlSchema IXmlSerializabl e.GetSchema()
{
return null;
}

void IXmlSerializabl e.WriteXml(XmlW riter writer)
{
writer.WriteStr ing(XmlConvert. ToString(this.v alue));
}

void IXmlSerializabl e.ReadXml(XmlRe ader reader)
{
this.value = XmlConvert.ToIn t32(reader.Read String());
}

}

The XML serialization as a XML element works without any problems:

class MyClass
{
[XmlElement("v")]
public MyInt32 myValue;
}

But when I mark myValue with the XmlAttributeAtt ribute:

class MyClass
{
[XmlAttribute("v ")]
public MyInt32 myValue;
}

I get:

System.InvalidO perationExcepti on: There was an error reflecting type
'ConsoleApplica tion.DTO'. ---> System.InvalidO perationExcepti on: There was
an
error reflecting field 'v'. ---> System.InvalidO perationExcepti on: Cannot
serialize member 'v'. XmlAttribute/XmlText cannot be used to encode
complex
types.
at
System.Xml.Seri alization.XmlRe flectionImporte r.ImportAccesso rMapping(Member Mapping
accessor, FieldModel model, XmlAttributes a, String ns, Type
choiceIdentifie rType)
at
System.Xml.Seri alization.XmlRe flectionImporte r.ImportFieldMa pping(StructMod el
parent, FieldModel model, XmlAttributes a, String ns)
at
System.Xml.Seri alization.XmlRe flectionImporte r.ImportStructL ikeMapping(Stru ctModel
model, String ns)
--- End of inner exception stack trace ---
at
System.Xml.Seri alization.XmlRe flectionImporte r.ImportStructL ikeMapping(Stru ctModel
model, String ns)
at
System.Xml.Seri alization.XmlRe flectionImporte r.ImportTypeMap ping(TypeModel
model, String ns, ImportContext context, String dataType, Boolean repeats)
--- End of inner exception stack trace ---
at
System.Xml.Seri alization.XmlRe flectionImporte r.ImportTypeMap ping(TypeModel
model, String ns, ImportContext context, String dataType, Boolean repeats)
at
System.Xml.Seri alization.XmlRe flectionImporte r.ImportElement (TypeModel
model, XmlRootAttribut e root, String defaultNamespac e)
at System.Xml.Seri alization.XmlRe flectionImporte r.ImportTypeMap ping(Type
type, XmlRootAttribut e root, String defaultNamespac e)
at System.Xml.Seri alization.XmlRe flectionImporte r.ImportTypeMap ping(Type
type)
at System.Xml.Seri alization.XmlSe rializer..ctor( Type type, String
defaultNamespac e)
at System.Xml.Seri alization.XmlSe rializer..ctor( Type type)
at ConsoleApplicat ion.Program.Mai n()

How can I serialize MyType as a XML attribute?

--
Paulo Morgado

[Paulo Morgado [MVP]]

Hi Chris. Thanks for your reply.

There are two things wrong in your approach to the problem:

1. Parse and ToString, at least in the way you showed, are all about
presentation and are culture dependente. XmlConvert should have been used,
but it's not extensible either.

2. You are not serializing MyValue and you are creating a new property that
I don't want my classes to have. I should have told that I already came to
this conclusion and also added an Obsolete attribute to warn developers not
to use that property.

I can understand that the XmlSerializer doesn't know how i will serialize my
type. There should be a IXmlSerilizable Something to serialize the type as
just a string and the XmlSerializer should handle it. Another way to do it
would be to let the XmlReader/XmlWriter to handle if proper XML was being
read/written.

--
Paulo Morgado

"Chris Lovett" wrote:

The XmlSerializer doesn't know that your IXmlSerializabl e just calls
WriteString. What if you called WriteElementStr ing instead? So the right
way to do this is expose a string Property

[XmlIgnore]
public MyInt32 MyValue;

[XmlAttribute("v ")]
public string myValue {
get { return MyValue.ToStrin g(); }
set { MyValue = MyInt32.Parse(v alue); }
}

[Paulo Morgado [MVP]]

Hi Chris,

Seems like I dumped my frustration on you. Sorry.

--
Paulo Morgado