Coping with Custom Object Serializers

Some aspects need to be initialized when a new instance of the class to which they are applied is created. For instance, instance-scoped aspects must be cloned from the prototype, and members imported through ImportMemberAttribute must be bound to aspect fields.

PostSharp enhances every constructor of every enhanced class so that aspects are properly initialized.

However, it is possible to create new instances of classes by bypassing the constructor. This happens, for instance, when classes are deserialized by the BinaryFormatter or the DataContractSerializer. These formatters use the method GetUninitializedObject(Type) to create new instances, but this method bypasses all constructors.

PostSharp implements a workaround for the deserializers BinaryFormatter and DataContractSerializer: it creates or modifies a method annotated by the custom attribute OnDeserializingAttribute, so that aspects are initialized properly.

However, if you are using a custom deserializer, or for any reason create instances using the method GetUninitializedObject(Type), you must initialize aspects manually.

Initializing Aspects Manually

There are two ways to initialize an aspect from user code.

By Defining a Method InitializeAspects

You can define in your classes (typically in one of the root classes of your class hierarchy) a method with the following name and signature:

protected virtual void InitializeAspects();

When PostSharp discovers this method, it adds its own initialization logic at the end of the InitializeAspects method, after the original logic. The original logic is not deleted. This method can safely have an empty implementation.

The following constraints apply:

• The method should be virtual unless the class is sealed.

• The method should be protected or public unless the class is internal.

For instance, the following class would enable aspects (applied to this class or on derived classes) to be initialized after deserialization (PostSharp automatically generates this code for BinaryFormatter and DataContractSerializer, so you need to write it manually only for a custom serializer).

[DataContract]
public abstract class BaseClass
{
    protected virtual void InitializeAspects()
    {
    }

    [OnDeserializing]
    private void OnDeserializingInitializeAspects(StreamingContext context)
    {
        this.InitializeAspects();
    }
}

By Invoking AspectUtilities.InitializeCurrentAspects

Instead of providing an empty method InitializeAspects, you can invoke the method InitializeCurrentAspects(). PostSharp translates a call to this method into a call to InitializeAspects. You must invoke it from a non-static method of an enhanced class.

If the class from which InitializeCurrentAspects() is invoked has not been enhanced by an aspect requiring initialization, the call to this method is simply ignored.