QList<double> => QVariant => QList<double>

[stefan]

Hi!

I'm trying to store my QList to QVariant and than convert it back to QList.

This is minimal example of what I'm trying to do. Real application would be more complex, but on same basis.

#include <QCoreApplication>
#include <QVariant>
#include <QList>
#include <iostream>
 
Q_DECLARE_METATYPE(QList<double>)
 
int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
 
    qRegisterMetaType<QList<double> >("QList<double>");
 
    QList<double> x1;
    for(int i=0; i<30; i++)
        x1.append((double)i);
 
    QVariant x2;
    x2.fromValue<QList<double> >(x1);
 
    QList<double> x3 = x2.value<QList<double> >();
    for(int i=0; i<x3.size(); i++)
        std::cout << x3[i] << "\n";
 
    std::cout << "***";
 
    return a.exec();
}

#include <QCoreApplication>
#include <QVariant>
#include <QList>
#include <iostream>

Q_DECLARE_METATYPE(QList<double>)

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    qRegisterMetaType<QList<double> >("QList<double>");

    QList<double> x1;
    for(int i=0; i<30; i++)
        x1.append((double)i);

    QVariant x2;
    x2.fromValue<QList<double> >(x1);

    QList<double> x3 = x2.value<QList<double> >();
    for(int i=0; i<x3.size(); i++)
        std::cout << x3[i] << "\n";

    std::cout << "***";

    return a.exec();
}

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Above code compiles without any warnings but running the code does not produce expected results.

Can somebody tell me what am I doing wrong?
Thanx!

[Santosh Reddy]

Does this look simpler

QList<QVariant> x1;
for(int i=0; i<30; i++)
    x1.append((double)i);
 
QVariant x2 = x1;
 
QList<QVariant> x3 = x2.toList();
for(int i=0; i<x3.size(); i++)
    std::cout << x3.at(i).toDouble() << "\n";

QList<QVariant> x1;
for(int i=0; i<30; i++)
    x1.append((double)i);

QVariant x2 = x1;

QList<QVariant> x3 = x2.toList();
for(int i=0; i<x3.size(); i++)
    std::cout << x3.at(i).toDouble() << "\n";

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[stefan]

Yes, this could solve my issue!
Thank you!

[anda_skoa]

You problem is here:

QVariant x2;
    x2.fromValue<QList<double> >(x1);

QVariant x2;
    x2.fromValue<QList<double> >(x1);

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QVariant::fromValue() returns a QVariant. It is a static method, it does not (cannot) change x2.

QVariant x2 = QVariant::fromValue(x1);

QVariant x2 = QVariant::fromValue(x1);

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Cheers,
_