Plugin interface with slots and signals

[anda_skoa]

Some things:
is the private inheritance of the interface class by accident?
you plugin implementation is missing the signals: section.
does GetWidget() return a valid widget pointer?
if yes, why don't you use that in the connect?

Cheers,
_

[mcarter]

Since you are requiring that all of the plugins have a MessageSend signal, just derived your initial plugin interface from QObject and include the signal there

class PluginWidgetInterface : public QObject
{
    Q_OBJECT
public:
    virtual ~PluginWidgetInterface() {}
    virtual QWidget * GetWidget() = 0;
signals:
    void MessageSend();
};

class PluginWidgetInterface : public QObject
{
    Q_OBJECT
public:
    virtual ~PluginWidgetInterface() {}
    virtual QWidget * GetWidget() = 0;
signals:
    void MessageSend();
};

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You will still need to use Q_OBJECT in your derived classes

class Plugin1 : public PluginWidgetInterface
{
    Q_OBJECT
    Q_PLUGIN_METADATA(IID "myplugins.Plugin1")
    Q_INTERFACES(PluginWidgetInterface)
public:
    ~Plugin1() {}
    QWidget * GetWidget();
};

class Plugin1 : public PluginWidgetInterface
{
    Q_OBJECT
    Q_PLUGIN_METADATA(IID "myplugins.Plugin1")
    Q_INTERFACES(PluginWidgetInterface)
public:
    ~Plugin1() {}
    QWidget * GetWidget();
};

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[folibis]

Since you are requiring that all of the plugins have a MessageSend signal, just derived your initial plugin interface from QObject and include the signal there

Ok, I derived interface class from QObject. Now, when I compile plugin dll I get lots of errors like:
error: undefined reference to `PluginWidgetInterface::qt_metacast(char const*)

I guess I have to put interface class in different library and link in statically with all plugins dlls but it looks too complicated

[mcarter]

As long as you are not linking against a statically built Qt then everythign should work fine.
The following code builds plugin lib in linux, and I think should build proper dll in windows

#ifndef _PLUGIN_WIDGET_INTERFACE_H_
#define _PLUGIN_WIDGET_INTERFACE_H_
 
#include <QtPlugin>
#include <QObject>
 
class PluginWidgetInterface : public QObject
{
    Q_OBJECT
public:
    virtual ~PluginWidgetInterface() {}
    virtual QWidget * GetWidget() = 0;
signals:
    void MessageSend();
};
 
#define PluginWidgetInterface_iid "myplugins.PluginWidgetInterface"
Q_DECLARE_INTERFACE(PluginWidgetInterface, PluginWidgetInterface_iid)
 
#endif

#ifndef _PLUGIN_WIDGET_INTERFACE_H_
#define _PLUGIN_WIDGET_INTERFACE_H_

#include <QtPlugin>
#include <QObject>

class PluginWidgetInterface : public QObject
{
    Q_OBJECT
public:
    virtual ~PluginWidgetInterface() {}
    virtual QWidget * GetWidget() = 0;
signals:
    void MessageSend();
};

#define PluginWidgetInterface_iid "myplugins.PluginWidgetInterface"
Q_DECLARE_INTERFACE(PluginWidgetInterface, PluginWidgetInterface_iid)

#endif

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#ifndef _PLUGIN1_H_
#define _PLUGIN1_H_
 
#include "plugininterface.h"
 
class Plugin1 : public PluginWidgetInterface
{
    Q_OBJECT
    //Q_PLUGIN_METADATA(IID "myplugins.Plugin1")
    Q_INTERFACES(PluginWidgetInterface)
public:
    ~Plugin1() {}
    QWidget * GetWidget();
};
 
#endif

#ifndef _PLUGIN1_H_
#define _PLUGIN1_H_

#include "plugininterface.h"
     
class Plugin1 : public PluginWidgetInterface
{
    Q_OBJECT
    //Q_PLUGIN_METADATA(IID "myplugins.Plugin1")
    Q_INTERFACES(PluginWidgetInterface)
public:
    ~Plugin1() {}
    QWidget * GetWidget();
};

#endif

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#include "plugin1.h"
 
QWidget * Plugin1::GetWidget()
{
    return 0;
}
 
Q_EXPORT_PLUGIN2(plugin1, Plugin1);

#include "plugin1.h"

QWidget * Plugin1::GetWidget()
{
    return 0;
}

Q_EXPORT_PLUGIN2(plugin1, Plugin1);

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TEMPLATE = lib
TARGET = 
DEPENDPATH += .
INCLUDEPATH += .
 
# Input
HEADERS += plugin1.h plugininterface.h
SOURCES += plugin1.cpp

TEMPLATE = lib
TARGET = 
DEPENDPATH += .
INCLUDEPATH += .

# Input
HEADERS += plugin1.h plugininterface.h
SOURCES += plugin1.cpp

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Can then be used with

QPluginLoader loader( qstrLibFilename );
PluginWidgetInterface * plugin = qobject_cast<PluginWidgetInterface *>(loader.instance());
QWidget * widget = plugin->GetWidget();
connect(plugin,SIGNAL(MessageSend()),this,SLOT(MessageReceived()));

QPluginLoader loader( qstrLibFilename );
PluginWidgetInterface * plugin = qobject_cast<PluginWidgetInterface *>(loader.instance());
QWidget * widget = plugin->GetWidget();
connect(plugin,SIGNAL(MessageSend()),this,SLOT(MessageReceived()));

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