converting QVariant to QList

mzimmers

Hi all -

I'd like to convert a QVariant to a QList, like this (if possible):

class EquipmentItem
{
    Q_GADGET
    ...
}
typedef QList<EquipmentItem> ZoneEquipmentList;
QVariant qv; //  does contain something in my real app.
ZoneEquipmentList zel = qv.toList();

In reading about this, I found this:

QList<QVariant> QVariant::toList() const
Returns the variant as a QVariantList if the variant has userType() QMetaType::QVariantList. If it doesn't, QVariant will attempt to convert the type to a list and then return it. This will succeed for any type that has registered a converter to QVariantList or which was declared as a sequential container using Q_DECLARE_SEQUENTIAL_CONTAINER_METATYPE. If none of those conditions are true, this function will return an empty list.QList<QVariant> QVariant::toList() const

I can't find anything on registering a converter. Can someone point me to the correct page for this?

Thanks...

PS: how best to format a passage from one of the Qt docs?

Chris Kawa

Simply use

ZoneEquipmentList zel = qv.value<ZoneEquipmentList>();

toList would give you QVariantList, not ZoneEquipmentList, meaning each element would be QVariant that you'd have to convert to your type. It's unnecessary overhead to convert them back and forth.

mzimmers

@Chris-Kawa that approach gives me a list of size 0. Do I need to write a converter for my list class?

JonB

@mzimmers said in converting QVariant to QList:

QVariant qv; // does contain something in my real app.

Can we start by making 100.0% sure we know what is in there? If qv.value<ZoneEquipmentList>() is empty list what does qv.toList() give you? And if that does give you something, what is inside the QVariant's in the list?

mzimmers

@JonB I just spoke with the author of the back end -- we had a misunderstanding about the contents of the message.

To answer your question, toList() does return a size of 1. But it's merely a UUID, not an actual equipment object as I'd expected.

I think my question is answered, but I'll hold off on closing this topic until I do a bit more experimentation.

Thanks...