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XML Serialization and Inherited Types

Asked 2008-08-21T14:30:53.497
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Following on from my previous question I have been working on getting my object model to serialize to XML. But I have now run into a problem (quelle surprise!).

The problem I have is that I have a collection, which is of a abstract base class type, which is populated by the concrete derived types.

I thought it would be fine to just add the XML attributes to all of the classes involved and everything would be peachy. Sadly, thats not the case!

So I have done some digging on Google and I now understand why it's not working. In that the XmlSerializer is in fact doing some clever reflection in order to serialize objects to/from XML, and since its based on the abstract type, it cannot figure out what the hell it's talking to. Fine.

I did come across this page on CodeProject, which looks like it may well help a lot (yet to read/consume fully), but I thought I would like to bring this problem to the StackOverflow table too, to see if you have any neat hacks/tricks in order to get this up and running in the quickest/lightest way possible.

One thing I should also add is that I DO NOT want to go down the XmlInclude route. There is simply too much coupling with it, and this area of the system is under heavy development, so the it would be a real maintenance headache!

c# xml inheritance serialization xml-serialization
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Problem Solved!

OK, so I finally got there (admittedly with a lot of help from here!).

So summarise:

Goals:

  • I didn't want to go down the XmlInclude route due to the maintenence headache.
  • Once a solution was found, I wanted it to be quick to implement in other applications.
  • Collections of Abstract types may be used, as well as individual abstract properties.
  • I didn't really want to bother with having to do "special" things in the concrete classes.

Identified Issues/Points to Note:

  • XmlSerializer does some pretty cool reflection, but it is very limited when it comes to abstract types (i.e. it will only work with instances of the abstract type itself, not subclasses).
  • The Xml attribute decorators define how the XmlSerializer treats the properties its finds. The physical type can also be specified, but this creates a tight coupling between the class and the serializer (not good).
  • We can implement our own XmlSerializer by creating a class that implements IXmlSerializable .

The Solution

I created a generic class, in which you specify the generic type as the abstract type you will be working with. This gives the class the ability to "translate" between the abstract type and the concrete type since we can hard-code the casting (i.e. we can get more info than the XmlSerializer can).

I then implemented the IXmlSerializable interface, this is pretty straight forward, but when serializing we need to ensure we write the type of the concrete class to the XML, so we can cast it back when de-serializing. It is also important to note it must be fully qualified as the assemblies that the two classes are in are likely to differ. There is

answered 2009-06-12T07:42:23.883

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