.NET deserializng an unknown object type from XML

[voodooflux]

I think it was. Point was just to check that OP wasn't relying on try catch to find out.

Cheers, just interested really.

[DimPrawn]

Do you happen to know if that post was pre .NET 2.0? Since then int.TryParse is available, and that doesn't use exceptions internally.

Bit off topic I know, just interested. Yes, and very bored today.

I think it was. Point was just to check that OP wasn't relying on try catch to find out.

[voodooflux]

From a blog:

Do you happen to know if that post was pre .NET 2.0? Since then int.TryParse is available, and that doesn't use exceptions internally.

Bit off topic I know, just interested. Yes, and very bored today.

[DimPrawn]

No I mean ask. CanDeserialise returns a boolean indicating if it can deserialise it. I don't know how it's implemented but I imagine it is reasonably efficient.

No it uses the root element name and namespace:

internal bool CanRead(int methodIndex, XmlReader xmlReader)
{
TempMethod method = this.methods[methodIndex];
return xmlReader.IsStartElement(method.name, method.ns);
}


So should be fine.

[ASB]

Why you say "ask" do you really mean try and catch exceptions?

That's a very slow process and not really a good pattern.

From a blog:

No I mean ask. CanDeserialise returns a boolean indicating if it can deserialise it. I don't know how it's implemented but I imagine it is reasonably efficient.

[DimPrawn]

The answer seems to be (with .NET 2) to create an array of types, get an array of serializers, ask each one whether it can deserialize the secified packet. That saves most of the messing about with trying to extract the root node name to infer the type information.

Why you say "ask" do you really mean try and catch exceptions?

That's a very slow process and not really a good pattern.

From a blog:

Anyway, C# is a little more “roll-up-your-sleeves” and solve your own problem, so there is no equivalent IsNumeric function in C#. This former student of mine asked if the following was an acceptable alternative:

public static bool isNumeric( string strText )
{
try
{
int i = int.Parse( strText ) ;
return true ;
}
catch
{
return false ;
}
}

What's wrong with this picture? This is classic lazy-programming (or, in this case, just inexperienced programming) because the person knows enough about C# to use try{}catch{}, but is using it inappropriately. Exceptions are for exceptional situations -- not for avoiding some real thinking through the issue. Catching exceptions is hard work on your programs and performance will really suffer: this try{}catch{} isNumeric() function is over 2,000 times slower than this alternative:

public static bool isNumeric( string strText )
{
char[] chars = strText.ToCharArray() ;
for ( int i = 0; i < chars.Length; i++ )
{
if( !Char.IsDigit( chars[ i ] ) ) //could also explore IsNumber
{
return false ;
}
}
return true ;
}

[ASB]

Sounds like you have design issues.

How comes you are not controlling the serialization?
Why don't you know what type the file contains until you open it?
Why are you having to resort to this bodge?

A crap design leads to crap bodges like you are contemplating.

It's interfacing to a system which simply sends an XML message over a TCP socket. The type is defined by the root node of the XML message. I didn't design that bit, I just have to interface with it.

The answer seems to be (with .NET 2) to create an array of types, get an array of serializers, ask each one whether it can deserialize the secified packet. That saves most of the messing about with trying to extract the root node name to infer the type information.

[DimPrawn]

Sounds like you have design issues.

How comes you are not controlling the serialization?
Why don't you know what type the file contains until you open it?
Why are you having to resort to this bodge?

A crap design leads to crap bodges like you are contemplating.

[ASB]

If you are controlling the serialization end too, you might be better off using the NetDataContractSerializer Class instead.

http://msdn.microsoft.com/en-us/libr...erializer.aspx

Since this serializer embeds the types and namespaces of the serialized objects into the XML, it does not need to know the type to deserialize them back into different objects.

Unfortunately I'm not controlling the serialization end.

It's not too much of a problem, there are only about 10 different messages. Pro-tem I guess I'll just have to parse them into an XML document and switch based on the name.

If I can be bothered I'll add something to the config file to give me the name of the root node and the type to deserialize it to. I can then get the type with reflection and create the deserializer.

It just "feels" such a mess.

Cheers.

[madeoff]

Do you know how the objects were serialised?
E.g. did it use a standard .NET serialisation method or a custom written one?

[DimPrawn]

If you are controlling the serialization end too, you might be better off using the NetDataContractSerializer Class instead.

http://msdn.microsoft.com/en-us/libr...erializer.aspx

Since this serializer embeds the types and namespaces of the serialized objects into the XML, it does not need to know the type to deserialize them back into different objects.

[Smurficus]

Would deserializing against an interface do the job? Or are they completely random objects?

[ASB]

I have a function which needs to deserialize an XML string, but it doesn't at this point know the object type.

So I get a string like:-

"<?xml version="1.0" encoding="utf-16"?>
<OneClass xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<SomeThing>Serializer.OneClass &lt;--This class type</SomeThing>
</OneClass>"

Or maybe:-

"<?xml version="1.0" encoding="utf-16"?>
<TwoClass xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<SomeThing>Serializer.TwoClass &lt;--This class type</SomeThing>
</TwoClass>"

And I want to end up with a "OneClass" or a "TwoClass".

I can do this by creating an xmlDocument, loading the XML, getting the documentelement.name, mapping that to a type via configuration information, and this then gives me the type which I can create an xmlSerializer from. Then I can deserialize it.

But surely there must a better way.

Stuffed if I can find it though. Any suggestions?

Cheers.