QWidget in a plugin [Solved]

luca

Hi all,
I'm playing for the first time with plugins and I'm doing some tests.

I'm trying to create a very simple QMainWindow that load a plugin at run-time and put it as its central widget.

All the plugins example I saw use plugins to add some function to the application, not a GUI (for example "this":http://doc.qt.nokia.com/4.7/tools-plugandpaint.html)

I need a very small example on how to define interface to contain a QWidget.

goetz

Have a look at the designer plugins, they return widgets among other things from the plugin.

andre

Plugins supplying widgets is really not all that magical.
While you can simply return a QWidget*, you might need to think about an interface that is a bit more specific to your application. In my application, I am using a Component class that functions as this base interface, and that can be extended with a set of other interfaces that may or may not be implemented by the plugin.

luca

Thanks,
I thought to the plugin because I need a way to update some widget of the application without the need to re-build all application.
The application should take the name of the plugins from a DB and than lists all them in a menu (if it find some plugins).

luca

I have a problem in using the plugin:

This is the interface:
@
#ifndef PLUGININTERFACE_H
#define PLUGININTERFACE_H

#include <QtPlugin>

class QWidget;

class PluginInterface
{
public:
virtual ~PluginInterface() {}
virtual QWidget* createWidget() = 0;
};

Q_DECLARE_INTERFACE(PluginInterface, "com.trolltech.Prova.PluginInterface/1.0")

#endif // PLUGININTERFACE_H

@

this is the plugin:
@
#ifndef PLUGIN_H
#define PLUGIN_H

#include <QObject>
#include <QWidget>
#include "plugininterface.h"

#include "widgetplugin.h"

class Plugin : public QObject, public PluginInterface
{
Q_OBJECT
Q_INTERFACES(PluginInterface)
public:
explicit Plugin(QObject *parent = 0);
QWidget *createWidget();

signals:

public slots:

};

#endif // PLUGIN_H

@

@
#include "plugin.h"

Plugin::Plugin(QObject *parent) :
QObject(parent)
{
}

QWidget * Plugin::createWidget()
{
return new WidgetPlugin();
}

@

the WidgetPlugin is a very simple plugin.

This is the MainWindow:
@
#include "plugininterface.h"

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);

QDir pluginsDir = QDir(qApp->applicationDirPath());

pluginsDir.cd("plugins");

foreach (QString fileName, pluginsDir.entryList(QDir::Files))
{
    qDebug() << fileName;
    qDebug() << pluginsDir.absoluteFilePath(fileName);
    QPluginLoader loader(pluginsDir.absoluteFilePath(fileName));
    //qDebug() << loader.loadHints();
    QObject *plugin = loader.instance();
    qDebug() << plugin;
    if (plugin)
    {
        PluginInterface *plugin_widget = qobject_cast<PluginInterface *>(plugin);
        if (plugin_widget)
        {
            this->setCentralWidget(plugin_widget->createWidget());
        }
    }
}

}
@

luca

After compiling the plugin I get a .so file:
@
libwidgetplugin.so
@

When I execute the MainWindow application I get in the debug:
@
"libwidgetplugin.so"
"/home/luca/mainwindow-build-desktop/plugins/libwidgetplugin.so"
QObject(0x0)
@

So it seems it isn't able to load plugin....

giesbert

where did you put the plugin (physically on the disk)?

luca

As you can see in the debug output, it find the plugin but it can't load it.

luca

I changed plugin.cpp :
@
#include "plugin.h"

QWidget * Plugin::createWidget()
{
return new WidgetPlugin();
}

Q_EXPORT_PLUGIN2(widgetplugin, Plugin)

@

I solved the problem, now it works...