QMetaType::registerConverter for a user-defined structure to QString.

yannickBAT

Hi everyone,

I'm currently working on a project and I need to develop my own conversion from a User-defined structure (let's call it "MyStructure"), which has already been defined as a Q_META_TYPE, to a QString.

Both functions "toQStringFromMyStructure" and "toMyStructureFromQString" are already written.
This is the time where I want to use the QMetaType::registerConverter(MemberFunction function).

My pseudo code would be like:

######################HEADER FILE#######################

struct MyStructure { ... }

class MyClass
{
public:
static QString toQStringFromMyStructure(MyStructure myStructure);
static MyStructure toMyStructureFromQString (QString qString);
}

######################CPPFILE##########################

// The constructor.
MyClass::MyClass() : m_value(value)
{
QMetaType::registerConverter<MyStructure, QString>(toQStringFromMyStructure);
}

######################################################

As you can image, the italic code line doesn't compile and is subject to all kind of errors.
I tried to adapt the given argument, such as "&toQStringFromMyStructure" or "*toQStringFromMyStructure" etc. but neither of them did work actually. Moreover, the Qt Documentation couldn't help me found my issue.

Please, do you have any idea ?
Could it be related to the fact that my converter functions are "static" ?
Could it be related to the fact that the registration is done in a class MyClass which is neither the original type nor the targeted type ?

Honestly I am totally lost with this - I have no doubt about that - powerful method.

Thank you in advance.

mrjj

Hi
The docs says
bool QMetaType::registerConverter(MemberFunction function)
so if it really means a member function, i doubt a static can be used as
its not a real member function since there is no "this" pointer involved.
So i would 100% try to have them as non static.
Also i wonder if MyClass should be QObject based and have Q_OBJECT macro.

SGaist

Hi and welcome to devnet,

Here is a small example:

#include <QCoreApplication>
#include <QMetaType>
#include <QTextStream>
#include <QtDebug>

class TestMe {
public:
    TestMe(int value=12):
        value(value)
    {}

    QString toString() const
    {
        return QString::number(value);
    }

private:
    int value;
};
Q_DECLARE_METATYPE(TestMe)

int main(int argc, char **argv)
{
    QCoreApplication app(argc, argv);

    QMetaType::registerConverter(&TestMe::toString);

    TestMe test;
    QVariant variant;
    variant.setValue(test);
    qDebug() << variant.toString();
    return 0;
}

yannickBAT

Thank you, both of you.

Since I couldn't solve the problem, I decided to adapt my code according to your example (in particular, I did create a new class which attributes are of type "MyStructure", etc.)

Anyways, it finally worked !

Thanks again,
See you soon !