How to convert QList<QVariant> to QList<T> - qt

Question

For my serialization method i need to store a QList<T> where T is my custom Type, in a QVariantList.
QList<T> l;
l.append(T());
QVariant var = QVariant::fromValue(l);
var.canConvert(QVariant::List); // returns true
//So i can easily iterate over the variant with sth like this:
QVariantList list;
QSequentialIterable it = var.value<QSequentialIterable>();
for (const QVariant &v : it)
list << v;
/* deserialization side */
var = list;
var.value<QList<T>>(); //returns an empty list which is not my serialized list;
My problem is that i cannot convert back the variant list into QList<T>
EDIT:
#define PROPERTY(type, name) \
Q_PROPERTY(type name MEMBER name) \
type name;
class Measurement
{
Q_GADGET
public:
PROPERTY(int, index)
PROPERTY(QString, name)
PROPERTY(QString, unit)
PROPERTY(double, factor)
PROPERTY(bool, isVisible)
PROPERTY(quint8, decimal)
bool operator ==(const Measurement &other)
{
return (this->index == other.index);
}
};
you can consider this class as my custom type (T). i also save the class name (here "Measurement") along with serialized data for furthur uses, because as you know we can get the registered type with QMetaType::type(char*) but with that type i can only construct a QVariant with QVariant(int typeId, const void *copy) but here i want to construct the QList<Measurement> itself.

Answer 1

You will need to deserialize the QVariant list one item at a time. I am also not sure that this line:
var = list;
is performing what you intended. It will take your QVariantList list and wrap it inside another QVariant called var, which is of type QVariant(QVariantList, (QVariant(MyType, ), QVariant(MyType, ))). There doesn't seem to be much benefit to doing this.
Nonetheless, the example below shows a way to recover the list from var.
#include <QCoreApplication>
#include <QVariant>
class MyType {
public:
MyType() {}
MyType(QString value) { m_value = value; }
QString m_value;
};
Q_DECLARE_METATYPE(MyType)
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QList<MyType> l;
l.append(MyType("foo"));
l.append(MyType("bar"));
QVariant var = QVariant::fromValue(l);
var.canConvert(QVariant::List); // returns true
//So i can easily iterate over the variant with sth like this:
QVariantList list;
QSequentialIterable it = var.value<QSequentialIterable>();
for (const QVariant &v : it)
list << v;
/* deserialization side */
var = list;
QList<MyType> deserializedList;
foreach(QVariant v, var.value<QVariantList>()) {
deserializedList << v.value<MyType>();
}
return a.exec();
}