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Is it possible that DataContractSerializer wrongly deserializes an object if the fields are not in the "correct" (whatever that means) order?

The classes that I try to serialize/deserialize do not have order-attributes placed on fields/properties. Yet one of my fields always gets deserialized as null even though it has a non-null value (it actually contains a list of strings).

When I moved two XML elements in serialized file around to match the order in another XML example (for which deserialization worked without problems) everything started to work.

This makes no sense to me but maybe someone knows better. ;)

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To be eligible for correct serialization / serialization by the DataContractSerializer, all of the following must be true.

  1. The class that must be serialized must have SerializableAttribute or DataContractAttribute set;
  2. The properties and fields of the class that must be serialized require the DataMemberAttribute set;
  3. The datatype of the serializable property or field must be serializable (i.e., have a public ctor and inherit ISerializable);
  4. The class that must be serialized must implement IExtensibleDataObject;
  5. Note: serializable fields can be either public or private.
  6. Members must be in alphabetical order or you should use the Order-property of the DataMemberAttribute.

So, the order of the declaration does matter. If members are not in alphabetical order, they are skipped. Look up this answer at StackOverflow for an example, perhaps it applies to your case.

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4 Comments

As of .NET 3.5 SP1, the first and the second rules can be omitted.
@Martin: r u sure? For instance, for web services, which require serializability, they require DataMemberAttribute still, even in .NET 4.0. Do you have a link to a reference? I'd be interested to read more on that (and then update my answer).
Link in rule 6 is dead
@bkribbs, thank, I have located a different link with similar content, apparently, that site went dead.

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