You only need to known which object you (un)serialized, I had a coworker who
made a Xml where the Object value was base64 encoded byte stream for the object
value. This is fairly simple to have the following xml tag
<data type="MyQObjectMetaTypeName" typeId="3245">base64 encoded string from
QDataStream goes here</data>
or even JSON format could do the same.
This should help you, if the type id is a basic type or a user defined type you
can react differently. So for your QObject class type only need to register to
QMetaType you can use the name into the type field to create the object and
then apply the data to that object operator>>() with that given object. Not
sure you need a factory with QMetaType if done properly.
________________________________
From: Jason H <jh...@gmx.com>
Sent: Wednesday, February 21, 2018 10:08:50 AM
To: Jérôme Godbout
Cc: interestqt-project.org
Subject: Re: [Interest] Serializing QSensorReading derived classes
Yeah, tha's about what I was guessing. So QObject-derived classes (which the
readings are) are not copy constructable. I thought long and hard about it,
and I'm having to implement a ReadingFactory class, which will serialize any
reading using non-QObject-derived class[es], then set*() for each property on
the QSensorReading class. But to not have to make 13 (or however many
sensorreadings) classes, I just made one class to handle them all.
About 1000 lines of code later, I think I have something that will work.
I was wondering if there was a generic QObject serialization facility, where I
can save a QObject instance to a file, probably as a class name or id, and then
a QVariantMap of properties and their values {QString,QVariantMap}? For narive
classes like the sensor readings, it would have been helpful. I'm going to look
at Qt Remote Objects later today.
https://doc.qt.io/qt-5.10/qtremoteobjects-gettingstarted.html
If anyone has any pointers (NPI) about deficiencies with this approach let me
know!
Sent: Wednesday, February 21, 2018 at 9:09 AM
From: "Jérôme Godbout" <godbo...@amotus.ca>
To: "Jason H" <jh...@gmx.com>, "interestqt-project.org"
<interest@qt-project.org>
Subject: Re: [Interest] Serializing QSensorReading derived classes
The serialization assume you known what type you are reading. If you have a
dynamic structure, you will need to add some info about the next data coming
(type or something). DataStream convert the object minimal data to byte and no
information about what those byte represent. You might have the type intelace
inside the datastream or you might do an header that tell the sequence of
object (I personnaly would prefer the 2nd choice since you can optimize the
sequence with a commun series). Ex:
type bytes series [1,2,354] where those type could be QVariant basic type or
user defined type that you could make a switch (could represent a single Type
of a series of chained types ex: 354 --> [QString, int, QVector3D,
MyCustomType]. This way you could reduce the type bytes series length and could
add the real data validation with data length and checksum if ever needed.
As for QDataStream it can serialize a lot of data type of of the box, but you
might need to add some operator to serialize some types. Here's the list of
supported data types:
http://doc.qt.io/qt-5/datastreamformat.html
You might need to extend the support to the QAcceleromterReading and
QAltimeterReading to do you own data reading and call the constructor with the
proper deserialized data.
________________________________
From: Interest <interest-bounces+godboutj=amotus...@qt-project.org> on behalf
of Jason H <jh...@gmx.com>
Sent: Wednesday, February 21, 2018 1:05:35 AM
To: interestqt-project.org
Subject: [Interest] Serializing QSensorReading derived classes
I'd like to serialize these values.
QAcceleromterReading has x,y,z properties, but to serialize this one, the
accelerometer mode should also be included.
But aside from that, I'm not clear on what I need to do. There's adding the
QDataStream << >> (QDataScream stream, QSensorReading reading) operators. But
that won't allow me to know what I'm reading, so I need to add a byte to know
what I'm deserializing, which means I should really do it via QVariant in the
QMetaType system.
qRegisterMetaType() and DECLARE_META_TYPE(). However, when I do this I get:
qmetatype.h:766: error: call to implicitly-deleted copy constructor of
'QAltimeterReading'
return new (where) T(*static_cast<const T*>(t));
^ ~~~~~~~~~~~~~~~~~~~~~~~~~
for each of the types.
What can I do to get this to work without having to write (derive) my own
classes?
I'm also wondering why this isn't supported already?
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