May I ask a few questions about implementing QML models in C++?
Apologies if I sound uninformed.
1) When a model is specified on the QML side, e.g. in
ComboBox {
model xxxxx;
and that model is supplied by the C++ code, does the object
returned by C++ have to a model object,
e.g. a QStringListModel or a QAbstractListModel? Or could it be a
simple QStringList in the case of a simple ListView or ComboBox?
I suspect the former applies.
2) When the model is returned from C++ to QML, must this be performed by
a C++ object that inherits from such a model class (e.g.
QAbstractListModel) or could it be any class (i.e. inheriting from an
arbitrary base class) that has an extractor method returning an
appropriate model?
3) Related to the above, within the Download-from-dc context, is the
model used by the QML is dependent on the specific standard built-in
methods provided by one of the standard model classes (let's say
QAbstractListModel) or can one implement an arbitrary extractor method
that returns a model (e.g a QStringListModel). To me it looks like the
latter is the case because QAbstracListModel does not have a standard
built-in method that returns the complete list.
4) Within the existing main.qml, selecting "Show GPS fixes" activates
the C++ qmlManager.populateGpsData() method that, in turn, activates
GpsListModel::instance()->update. The appropriate (now updated) model
is m_instance, returned by GpsListModel::instance().
[So syntactically the :: operator has priority over the -> operator,
because instance()->update() does not make sense.]
Is my understanding correct here?
Now, the actual display of GPS data is done in gpsList.qml, using
gpsModel as a model and formatted by gpsDelegate. But I cannot link
gpsModel back to main.qml, QMLManager or to GpsListModel. Where is the
link made between gpsModel in gpsList.qml and the underlying C++ code?
As discussed before I would have used
ctxt->setContextProperty("gpsModel",
QVariant::fromValue(gpsQStringList)) but this is clearly not the case here.
5) If I understand it correctly, one can let DownloadManager inherit
from QAbstractListModel, then let DownloadManager have two extractor
methods, getVendorModel() and getProductModel() that each return an
appropriate and populated model, callable from QML. Does this make sense
at all?
I hope my questions are clear, and thank you so much for your time in
answering.
Kind regards,
willem
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