JB_NodeModel has no default constructor - Why?

jeffB100

I'm trying to register a C++ JB_NodeModel in the Qml Engine. JB_NodeModel inherits QAbstractItemModel.
I get this error:

"call to implicitly-deleted default constructor of QQmlElement<JB_NodeModel> - default constructor of QQmlElement<JB_NodeModel> is implicitly deleted because base class JB_NodeModel has no default constructor."

But I can't see a problem with the default constructor.
Any help would be greatly appreciated.

I've used initialiser lists but doesn't seem to help.

Here is a cut down version of JB_NodeModel.h :

class SP3CORESHARED_EXPORT JB_NodeModel : public QAbstractItemModel
{
    Q_OBJECT
public:
 explicit JB_NodeModel(QObject *parent = nullptr);

~JB_NodeModel();

protected:
    JB_Node* rootNode;
    JB_Node* actingRootNode;
    bool isValidURL(QString fieldName, JB_Node* node) const;

    QVector<QString> columnHeadingsV;    
    QHash<int, QVector<QString>> mapped_dbFieldNamesH;    
    QList<QString> unEditableDBFieldNamesList;
    QList<QString> editableCheckBoxDBFieldNamesList; 

private:
    JB_DatabaseManager& mDB;
    int jobID;
    int numOfLevels;
    QSharedPointer<JB_NodeModelHelpProt> nodeModelHelper;
    QVector<QSharedPointer<QHash<QString, JB_Node*>>> nodesHV;     
    QVector<JB_Node*> alteredNodesV;
    bool isTreeModel;
    bool canEmitDataChanged;
 
 };

Here is JB_NodeModel.cpp constructor source:

JB_NodeModel::JB_NodeModel(QObject *parent)
: QAbstractItemModel(parent),
  rootNode(nullptr),
  actingRootNode(nullptr),
  mDB(JB_DatabaseManager::instance()),
  jobID(aJobID),
  numOfLevels(1),
  nodeModelHelper(nullptr),
  isTreeModel(true),
  canEmitDataChanged(true),
  dragDropHelper(false)
{
    QSharedPointer<JB_NodeModelHelpProt> aNodeModelHelper(new JB_NodeModHelp_TreeGrpPers());
    nodeModelHelper = aNodeModelHelper;

    canEmitDataChanged = true;
    dragDropHelper = false;

    Q_ASSERT(!nodeModelHelper.isNull());

    alteredNodesV.clear();

    rootNode = nullptr;
    actingRootNode = nullptr;

etc. - please note I have implemented the virtual functions such as index and data etc but a lot of code so haven't included it here

And here is registering in QML engine:

#include <QGuiApplication>
#include <QQmlApplicationEngine>
#include <QQmlContext>

#include "A_Models/JB_NodeModel.h"

int main(int argc, char *argv[])
{
    QCoreApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
    QGuiApplication app(argc, argv);

    qmlRegisterType<JB_NodeModel>("JB_NodeModel", 1, 0, "JB_NodeModel");

    QQmlApplicationEngine engine;

    const QUrl url(QStringLiteral("qrc:/main.qml"));
    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
                     &app, [url](QObject *obj, const QUrl &objUrl) {
        if (!obj && url == objUrl)
            QCoreApplication::exit(-1);
    }, Qt::QueuedConnection);
    engine.load(url);

    return app.exec();
}

And here is the relevant part of qqmlprivate.h surrounding QQmlElement:

class QJSEngine;
class QQmlEngine;
class QQmlCustomParser;
namespace QQmlPrivate
{
    void Q_QML_EXPORT qdeclarativeelement_destructor(QObject *);
    template<typename T>
    class QQmlElement final : public T
{
public:
    ~QQmlElement() override {
        QQmlPrivate::qdeclarativeelement_destructor(this);
    }
    static void operator delete(void *ptr) {
        // We allocate memory from this class in QQmlType::create
        // along with some additional memory.
        // So we override the operator delete in order to avoid the
        // sized operator delete to be called with a different size than
        // the size that was allocated.
        ::operator delete (ptr);
    }
    static void operator delete(void *, void *) {
        // Deliberately empty placement delete operator.
        // Silences MSVC warning C4291: no matching operator delete found
    }
};


template<typename T>

// Error occurs on next line

void createInto(void *memory) { new (memory) QQmlElement<T>; }

template<typename T>
QObject *createParent(QObject *p) { return new T(p); }

dheerendra

How are you creating the object of JB_NodeModel ? I suspect some issue with member variable you have declared & initialised them. May be you can comment all those member variable initialisation & try creating the object.

IntruderExcluder

@jeffB100 said in JB_NodeModel has no default constructor - Why?:

qmlRegisterType<JB_NodeModel>("JB_NodeModel", 1, 0, "JB_NodeModel");

Can you try to change 1st parameter to something another, maybe "MyModels"?