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Editorial Team
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Asked: 2026-05-27T12:36:53+00:00

I try to load to plugins. If they are loaded with success , then

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I try to load to plugins. If they are loaded with success , then i must connect returned widgets.

With one plugin i create an action and add it to a menu , with another plugin i create a label and add it to window. Even if i get this error during runtime (when app loads plugins) , these two widgets are created and are visible. But there is no connection between them.

This is how i try to connect widgets 

QObject *plugin = pluginLoader.instance();
if (plugin) {
    myAction = qobject_cast<ActionInterface *>(plugin);

    if (myAction) {
        pluginMenu->addAction(myAction->newAction());
        verify ++;
    }

    myLabel = qobject_cast<LabelInterface *>(plugin);

    if (myLabel) {            
        layout->addWidget(myLabel->newLabel());
        verify++;
    }

    if (verify == 2)
        connect(myAction, SIGNAL(pushMyAction()),
            myLabel, SLOT(setTextforLabel()));
    }

    ...
}

Error message is :

QObject::connect: Cannot connect (null)::pushMyAction() to LabelPlugin::setTextforLabel()

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1 Answer

  1. Editorial Team
    QObject *plugin = pluginLoader.instance();
if (plugin) {

    if (plugin->inherits("ActionInterface")) {
        myAction = qobject_cast<ActionInterface *>(plugin);
        pluginMenu->addAction(myAction->newAction());
    }

    if (plugin->inherits("LabelInterface")) {            
        myLabel = qobject_cast<LabelInterface *>(plugin);
        layout->addWidget(myLabel->newLabel());
    }

    if (myLabel && myAction)
        connect(myAction, SIGNAL(pushMyAction()),
            myLabel, SLOT(setTextforLabel()));
    }

    ...
}

    Remove this “ugly” verify counter. Remember to initialize myLabel and myAction with NULL

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