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...