Serialization byte array vs XML file

Question

I am heavily using byte array to transfer objects, primitive data, over the network and back. I adapt java's approach, by having a type implement ISerializable, which contains two methods, as part of the interface, ReadObjectData and WriteObjectData. Any class using this interface, would write date into the byte array. Something Like that

  class SerializationType:ISerializable
    {
       void ReadObjectData (/*Type that manages the write/reads into the byte array*/){}
       void WriteObjectData(/*Type that manages the write/reads into the byte array*/){}  
    }

After write is complete for all object, I send an array of the network.

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This is actually two-fold question. Is it a right way to send data over the network for the most efficiency (in terms of speed, size)?

Would you use this approach to write objects into the file, as opposed to use typically xml serialization?

Edit #1

Joel Coehoorn mentioned BinaryFormatter. I have never used this class. Would you elaborate, provide good example, references, recommendations, current practices -- in addition to what I currently see on msdn?

Answer 1

If you are after simple, lightweight and efficient binary serialization, consider protobuf-net; based on google's protocol buffers format, but implemented from scratch for typical .NET usage. In particular, it can be used either standalone (via protobuf-net's Serializer), or via BinaryFormatter by implementing ISerializable (and delegating to Serializer).

Apart from being efficient, this format is designed to be extensible and portable (i.e. compatible with java/php/C++ "protocol buffers" implementations), unlike BinaryFormatter that is both implementation-specific and version-intolerant. And it means you don't have to mess around writing any serialization code...