Qt 4.8 to 5.0 - QPluginLoader->instance returns NULL

[Feyh]

Hello there,

I've written an Application by using QT 4.8.2. It does dynamically load different plugins to provide multiple functions for the user.
Now Qt5 was released and I wanted to convert my project to the newest version.

I got everything to work, except loading the plugin with QPluginLoader->instance(). While using Qt 4.8.2 it worked fine.

->errorString says:
"The file '.../plugins/nlprod.dll' is not a valid Qt plugin."

That's my code:

PluginLoader.cpp:
@
//"fileName" contains the name of the .dll
pluginLoader->setFileName(pluginsDir->absoluteFilePath(fileName));

    //"a" contains the correct path + name of the .dll
    QString a = pluginLoader->fileName();       

    //"plugin" is null and success "false"
    QObject *plugin = pluginLoader->instance();
    bool success = pluginLoader->isLoaded();

@

MyPlugin.h:
@
class NLPro : public QObject, IConnection
{
Q_OBJECT
Q_PLUGIN_METADATA(IID "NLPro" FILE "nlpro.json") // <- New since I've ported to Qt 5
Q_INTERFACES(IConnection)
...
}
@

MyPlugin.cpp:
I've deleted the following:
@
Q_EXPORT_PLUGIN2(NLPro, NLPro);
@

and I've added a .json-file with the following content:
@
{ "Keys": [ "NLPro"] }
@

Any idea?

Thanks in advance!

Regards