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Currently, I do serialize my model object to the SharedObject instance: 

 try {

     var mySo:SharedObject = SharedObject.getLocal("sig");

     mySo.clear();
     mySo.data.model = _model;
     mySo.flush();

  } catch ( e:Error ) {

    Alert.show( 'Leider konnte kein Modell geladen werden.' );

  }

Likewise, I load the saved model using the SharedObject instance. Works great.

Ultimately, I'd like to serialize it to a file - which fails. Here is how:

 var fp: File = File.applicationStorageDirectory;

 fp = fp.resolvePath( PREFS_FILENAME );

 var    _prefsStream:FileStream;
 _prefsStream = new FileStream();
 _prefsStream.open( fp, FileMode.WRITE );
 _prefsStream.endian = Endian.BIG_ENDIAN;

_model.writeExternal( _prefsStream );
_prefsStream.close();

The complementing read operation suddenly breaks and reports missing bytes.

In fact, I can't image how FileStream / _model.writeExternal() is able to serialize, since it needs to somehow know, that a new serialization operation is about to start. If it doesn't know, it won't be able to determine, which object instances are left to serialize.

Thus, I image that my concept is completely wrong or I missed how to initialize the serialization operation.

Please explains, what I'm missing.

I'd be happy to read the raw ByteArray from the shared object and write it to a file. Unfortunately, I didn't find a method to retrieve from a SharedObject a ByteArray of a certain property, in my case mySo.data.model. My question is loosely related to this one: Why does delete( DictionaryInstance[ key ] ); fail?

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SteAp
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1 Answers1

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I once had to perform unit tests on an externalization framework I built and this is how I did it:

byteArray.writeObject(myObject);
byteArray.position = 0;
readValue = byteArray.readObject();

Also, I don't think you should have to worry about byte order, I think the default is big endian anyways.

So, for your case, I think you need something like:

fileStream.writeObject(myObject)

as opposed to:

myObject.writeExternal(_prefsStream);

The runtime should call writeExternal on your model automagically.

Naftuli Kay
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  • Regarding the byte order: Wanted to make sure that the code is cross-platform. Just to make sure ;-) Ah, writeObject() might be the essential point! Let's see. Will come back... – SteAp Oct 10 '11 at 20:54
  • Thank you very much! Great hint! OK, writeObject() seems to prepare/maintain the list of already serialized object instances and all the magical rest. Still: How does writeObject() know, that a fresh serialization operation just started? I mean, how does it know, that it needs to save all reachable object instances? – SteAp Oct 10 '11 at 20:58
  • It crawls the object tree. For example, every call to `writeObject` does a test to see if the object implements `IDataOutput` or `IExternalizable`. If so, it calls `writeExternal` on the object to give it a chance to serialize itself. If not, it tries to serialize it as best as it can (using public properties etc.) or if it's a simple object (ie String, Number, Object, Array, etc) it simply calls into those methods to serialize it. I've served my time fighting with `IExternalizable`, but once you get the hang of it, you can do pretty cool stuff. – Naftuli Kay Oct 10 '11 at 21:05
  • Also, so if a custom class serializes another custom class, it just repeats and keeps crawling the tree until the entire tree is serialized. – Naftuli Kay Oct 10 '11 at 21:06
  • But suppose I call writeExternal later on again. The runtime somehow needs to know, that a fresh serialization operation is about to start. Doesn't it? – SteAp Oct 10 '11 at 21:15
  • Why would you manually call `writeExternal`? The runtime calls that for you when you call `writeObject`. – Naftuli Kay Oct 10 '11 at 23:23
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    Type. Rule of thumb: To serialize, implement the methods writeExternal() and readExternal(): Inside these routines and which writing to or reading from a serialization destination/source, always use writeObject() and readObject(). – SteAp Oct 11 '11 at 20:35