Is it possible to connect a signal to a static slot without a receiver instance?

Question

Is it possible to connect a signal to static slot without receiver instance?

Like this: connect(&object, SIGNAL(some()), STATIC_SLOT(staticFooMember()));

There is a QApplication::closeAllWindows() function with [static slot] attribute in Qt documentation. And there is an example of using it from the documentation:

exitAct = new QAction(tr("E&xit"), this); exitAct->setShortcuts(QKeySequence::Quit); exitAct->setStatusTip(tr("Exit the application")); connect(exitAct, SIGNAL(triggered()), qApp, SLOT(closeAllWindows())); 

Is it allowed to do the same action but without passing an instance variable (e.g. when a class has only static functions)?

class Some : public QObject {     Q_OBJECT public slots:     static void foo(); private:     Some(); }; 

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Maybe Frank Osterfeld is right and it is better to use singleton pattern in this case but I am still surprised why this feature has not been implemented yet.

Update:

In Qt 5 it is possible.

Answer 1

Update for QT5: Yes you can

static void someFunction() {     qDebug() << "pressed"; } // ... somewhere else QObject::connect(button, &QPushButton::clicked, someFunction); 

In QT4 you can't:

No it is not allowed. Rather, it is allowed to use a slot which is a static function, but to be able to connect it you need an instance.

In their example,

connect(exitAct, SIGNAL(triggered()), qApp, SLOT(closeAllWindows())); 

means than they previously called

QApplication* qApp = QApplication::instance(); 

Edit:

The only interface for connecting object is the function

bool QObject::connect ( const QObject * sender, const QMetaMethod & signal, const QObject * receiver, const QMetaMethod & method, Qt::ConnectionType type = Qt::AutoConnection ) 

How are you going to get rid of const QObject * receiver?

Check the moc files in your project, it speaks by itself.

Answer 2

It is. (With Qt5)

#include <QApplication> #include <QDebug>  void foo(){     qDebug() << "focusChanged"; }   int main(int argc, char *argv[]) {     QApplication app(argc, argv);     QObject::connect(&app, &QApplication::focusChanged, foo);     return app.exec(); }