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I have an invokable c++ function that I call from a QML file. I would like this function to accept a list of javascript objects (or maps) as an argument. The Qt documentation indicates that javascript lists are translated to QVariantList, and javascript objects to QVariantMap. (see here, last paragraph of the section).

Similarly, if a C++ type uses a QVariantList or QVariantMap type for a property type or method parameter, the value can be created as a JavaScript array or object in QML, and is automatically converted to a QVariantList or QVariantMap when it is passed to C++.

Unfortunately, when the argument is typed as a QVariantList, QList<QVariant> or even QVariant(then translated to a QList<QVariant>) the length returned is 0. I also tried having it typed as a QList<QObject*> and the length of the list can be read, but I can't access the data inside as a QObject* cannot be cast to a QVariant.

QML code excerpt:

for(currentLabel = 0; currentLabel<acquisitionsLabels.length; currentLabel++)
 label = acquisitionsLabels[currentLabel];
 link = db.getLinkFromLabel(label)[0];
 structureName="";
 if(link)
 criteria = db.getCriteriaFromId(link.fkCriteria);
 structure = db.getStructureFromId(criteria.fkStructure);
 structureName = structure.name;
 
 labels.push(
 "label":label,
 "structureName":structureName,
 "moreToCome":currentLabel<acquisitionsLabels.length-1
 );

console.log(labels.length);
exportReportFile.printAcquisition(acquisition, acquisitionRenderer.renderAcquisition(acquisition), labels);

exportReportFile.cpp excerpt:

void ExportReportFile::printAcquisition(QObject *a_acquisition, const QVariant& a_labels)
 QList<QVariant> l_labels = a_labels.value<QList<QVariant>>();
 std::cout << typeid(l_labels).name() << std::endl;
 std::cout << l_labels.count() << std::endl;
 if(l_labels.length()>0)
 for(int i=0;i<l_labels.count();i++) 
 auto item = l_labels.at(i);
 std::cout << typeid(item).name() << std::endl;
 
 

This version is with the argument being a QVariant reference, but I also tried with all previously cited types.

The expected output for a list that is 3 items long would be:

qml: 3
class QList<class QVariant>
3
class QVariant
class QVariant
class QVariant

and it actually is

qml: 3
class QList<class QVariant>
0

Create a method that takes a QJSValue as parameter. This way the value is not converted to QVariant but the actual JS data is returned. You can then continue doing stuff with that as you please, including the conversion to QVariant, if needed:

void ExportReportFile::printAcquisition(QObject *a_acquisition, const QJSValue& a_labels) 
 // do stuff with it:
 const int length = jsArray.property("length").toInt();
 for (int i = 0; i < length; ++i) 
 auto arrayElement = jsArray.property(i);
 // now you have the element etc.