QPluginLoader failed to load plugins (available for both linux and windows)

1. ErrorString: failed to extract plugin meta data from this problem

Reason 1: The interface implementation class does not have Q_OBJECT

Reason 2: The Q_PLUGIN_METADATA statement was made, but the json file format is wrong

2. The problem of PluginLoader returns a QObject instance, but qobject_cast returns null (0x0) appears

Reason 1: The interface files are not uniform and the id of Q_DECLARE_INTERFACE is different

 

Interface file:

#ifndef APPINTERFACE_H
#define APPINTERFACE_H

#include <QtPlugin>
QT_BEGIN_NAMESPACE
class QWidget;
class QString;
class QObject;
QT_END_NAMESPACE

class AppInterface
{
public:
    virtual ~AppInterface(){}
    virtual QWidget *CreateWidget(QWidget *parent = nullptr)=0;
    virtual QString name() = 0;
};
Q_DECLARE_INTERFACE(AppInterface, "id1233");
#endif // APPINTERFACE_H

Plug-in implementation class file:

#ifndef MYPLUGIN_H
#define MYPLUGIN_H

#include <QObject>
#include "appinterface.h"

class MyPlugin : public QObject, public AppInterface
{
    Q_OBJECT

    Q_PLUGIN_METADATA(IID "org.qt-project.Qt.QGenericPluginFactoryInterface" FILE "plugin.json")
    Q_INTERFACES(AppInterface)

public:

    QWidget *CreateWidget(QWidget *parent);
    QString name();
};

#endif // MYPLUGIN_H