Saving or Loading from QJson not working (?)

Ediolot

Hi all, Im new to the use of QJson and Im learning it with a loading/saving bookmarks browser feature.

Im working in windows.
I included this in the .h :
...

#include <QFile>
#include <QJsonArray>
#include <QJsonDocument>
#include <QVariantList>
#include <QVariant>
#include <QMetaType>
...

This is the code for the save:

void BookMarksBar::saveBookMarks() {

qDebug()<<"Saving";
QFile bookMarksFile("bkms.dat");

if (!bookMarksFile.open(QFile::WriteOnly | QFile::Truncate))
{
    bookMarksFile.close();
    return;
}

QJsonArray list = QJsonArray::fromVariantList(ToQVariantList(bookMarksList_));
QJsonDocument saveDoc(list);

for (int i=0; i<ToQVariantList(bookMarksList_).size(); i++)
{
    qDebug()<<ToQVariantList(bookMarksList_).at(i).value<BookMark>().getIcon();
    qDebug()<<ToQVariantList(bookMarksList_).at(i).value<BookMark>().getName();
    qDebug()<<ToQVariantList(bookMarksList_).at(i).value<BookMark>().getUrl();
}

bookMarksFile.write(saveDoc.toBinaryData());
bookMarksFile.close();

}

And this is the load function:

void BookMarksBar::loadBookMarks() {

qDebug()<<"Loading";
QFile bookMarksFile("bkms.dat");

if (!bookMarksFile.open(QFile::ReadOnly) || bookMarksFile.atEnd())
{
    bookMarksFile.close();
    return;
}

QJsonDocument loadDoc(QJsonDocument::fromBinaryData(bookMarksFile.readAll()));
bookMarksList_ = FromQVariantList(loadDoc.array().toVariantList());

for (int i=0; i<bookMarksList_.size(); i++)
{
    qDebug()<<bookMarksList_[i].getIcon();
    qDebug()<<bookMarksList_[i].getName();
    qDebug()<<bookMarksList_[i].getUrl();
}

for (int i=0; i<bookMarksList_.size(); i++)

    addBookMark(bookMarksList_[i].getIcon(),
                bookMarksList_[i].getName(),
                bookMarksList_[i].getUrl());

bookMarksFile.close();

}

When I use the save function, I get this output as expected:
Saving
QIcon(null)
"DuckDuckGo"
QUrl( "https://duckduckgo.com/" )

But, when I load, I get nothing:
Readed
QIcon(null)
""
QUrl( "" )

Just in case you need to know, this is from the class (BookMarksBar):

private:

QList<BookMark> bookMarksList_;

QVariantList ToQVariantList(const QList<BookMark> &list);
QList<BookMark> FromQVariantList(const QVariantList &list);

And those two functions:

QVariantList BookMarksBar::ToQVariantList(const QList<BookMark> &list) {

QVariantList newList;
QVariant     newVar;

for (int i=0; i<list.size(); i++)
{
    newVar.setValue(list[i]);
    newList.append(newVar);
}

return newList;

}

QList<BookMark> BookMarksBar::FromQVariantList(const QVariantList &list) {

QList<BookMark> newList;

for (int i=0; i<list.size(); i++)

    newList.append(list[i].value<BookMark>());

return newList;

}

Thanks

mcosta

With JSON a simple way to Debug is to read the generated JSON and check if it looks like you expect.

Ediolot

@mcosta I have just tried it and yes, the problem is here.

This is the .json file:

[
null
]

But what is worng in the code? Im just saving a QVariantList

QJsonArray list = QJsonArray::fromVariantList(ToQVariantList(bookMarksList_));
QJsonDocument saveDoc(list);

Ediolot

I tried this:

typedef struct
{
QString i;
} stBookMark;

Q_DECLARE_METATYPE(stBookMark)

In .cpp:

stBookMark x;
x.i = "Hello";

QVariant c;
c.setValue(x);

QVariantList a;
a.append(c);
a.append(0);
a.append(-119);

qDebug()<<a;

QJsonArray list = QJsonArray::fromVariantList(a);
QJsonDocument saveDoc(list);
qDebug() output: (QVariant(stBookMark, ) , QVariant(int, 0) , QVariant(int, -119) )

And the output .json file here:

[
null,
0,
-119
]

? Offline

Hi,
IMHO the problem is that QJsonValue QJsonValue::fromVariant(const QVariant & variant) (http://doc.qt.io/qt-5/qjsonvalue.html#fromVariant) can't convert BookMark to QJsonObject. I don't think that adding a custom converter with QMetatype::registerConverter() would help. Looks like you have to do the conversion to QJsonArray yourself.
Cheers!
Wieland