Problem with Plugin Marcos: Error on Constructor Argument Count

ModelTech

I am trying to make my application customizable by enabling the creation of plugins. I am using the Plug & Paint example as basis, but I am experiencing a build problem that refers to the expansion of Qt macros. I do not see what I should change to fix it. Hopefully somebody can help. The build error is the following and complains about the number of arguments for the constructor.

moc_sdf3import.cpp:9: from moc_sdf3import.cpp:9:
moc_sdf3import.cpp:-1: In function ‘QObject* qt_plugin_instance()’:
moc_sdf3import.cpp:157: error: no matching function for call to ‘DFM::SDF3Import::SDF3Import()’
 QT_MOC_EXPORT_PLUGIN(DFM::SDF3Import, SDF3Import)
                           ^
Qt5.7/5.7/gcc_64/include/QtCore/qplugin.h:112: in definition of macro ‘Q_PLUGIN_INSTANCE’
                 _instance = new IMPLEMENTATION; \
                                 ^
moc_sdf3import.cpp:157: in expansion of macro ‘QT_MOC_EXPORT_PLUGIN’
 QT_MOC_EXPORT_PLUGIN(DFM::SDF3Import, SDF3Import)
 ^
moc_sdf3import.cpp:9: In file included from moc_sdf3import.cpp:9:0:
sdf3import.h:17: candidate: DFM::SDF3Import::SDF3Import(DFM::Model*, QFile*)
     explicit SDF3Import(Model *, QFile *);
              ^
sdf3import.h:17: note:   candidate expects 2 arguments, 0 provided

To enable your help, here are some of the classes that I am using for this. First is a base Interface class (interface.h) from which I derive a number of Plugin Interfaces:

#include <QDialog>
#include "../model/model.h"

namespace DFM {

class Interface {
public:
    explicit Interface(Model *S);
    virtual ~Interface() { }
    virtual const QString name() = 0;
    virtual const QVersionNumber version() = 0;
    QDialog *preDialog();
    void preProcess();
    QDialog *postDialog();
    void postProcess();
protected:
    Model* Specification;
};

}

The header file (importer.h) of the derived interface class that is relevant for this sdf3import.cpp class is as follows:

#include <QtPlugin>
#include <QFile>
#include "interface.h"
#include "../base/issue.h"

namespace DFM {

class DFMCORESHARED_EXPORT Importer : public Interface {

public:
    explicit Importer(Model *, QFile *);
    virtual ~Importer();
    bool hasIssues();
    bool hasErrors();
    virtual void read() = 0;
    QList<Issue *> &issues();
protected:
    QList<Issue *> Issues;
    QFile *File;
};

}

#define ImportInterface_ID "AUniqueString.ImportInterface"
Q_DECLARE_INTERFACE(DFM::Importer, ImportInterface_ID)

These complete the part of my dfmcore library. Now, I use these to create a plugin in a different project. The sdf3import.h file looks as follows:

#include <dfmcore.h>

namespace DFM {

class SDF3Import : public QObject, public Importer {
    Q_OBJECT
    Q_PLUGIN_METADATA(IID "AUniqueString.ImportInterface")
    Q_INTERFACES(DFM::Importer)

public:
    explicit SDF3Import(Model *, QFile *);
    const QString name() override;
    const QVersionNumber version() override;
    void read() override;
    QDialog *postDialog();
    void postProcess();
};

}

The sdf3import.cpp file is not at all interesting, but to be sure, here is a part of the constructor:

SDF3Import::SDF3Import(Model *S, QFile *F) : QObject(), Importer(S, F) { }

jsulm

@ModelTech said in Problem with Plugin Marcos: Error on Constructor Argument Count:

explicit SDF3Import(Model *, QFile *);

You don't have default constructor.

ModelTech

Do you mean that I must also have a constructor with 0 arguments like in

explicit SDF3Import(Model * = NULL, QFile* = NULL)

Well, I have tried this and it does solve the build issue. But how can I avoid this default with 0 arguments (I would like to do so...)

ModelTech

Now that I got it to work, I discovered how it actually works and that I shouldn't use those arguments to the constructor at all. Instead, I should have such arguments to the methods that I want for the interface: The interface object is always created at loading the plugin (which is not what I anticipated...) So, problem solved!