Passing different classes in connect() in Qt - c++

Question

I'm working on a image editing software which includes a few classes. But I need my code to be more generic. But I've got a big problem with my classes when it comes to connections.
QObject::connect(actionSmartContrast, SIGNAL(triggered(bool)), effectsWindow, SLOT(addSmartContrast()));
QObject::connect(actionSaturation, SIGNAL(triggered(bool)), effectsWindow, SLOT(addSaturation()));
I've got a Menu called "Effects", and when the user clicks the QAction actionSmartContrast, then the effect Smart Contrast is added to my effects window. The thing is, given that each effect has its own class, I have to create a function for each class as you can see in the code above. And this is very repetitive. I would like to avoid this problem by doing something like this:
QObject::connect(actionSmartContrast, SIGNAL(triggered(bool)), effectsWindow, SLOT(addEffect(new SmartContrast())));
QObject::connect(actionSaturation, SIGNAL(triggered(bool)), effectsWindow, SLOT(addEffect(new Saturation())));
Everything would be fine for the function addEffect() because it expects a pointer to an Effect object and both SmartContrast and Saturation inherit from Effect. The only problem is that it is impossible to pass variables in connect() like this. So I thought of subclassing QAction and creating a signal which would return the class I like everytime but again, how to tell my new Action class what class it should return? If I have a thousand effects, I won't subclass QAction a thousand times! I need to create a function which would take for example a pointer to a SmartContrast object and it will guess that it has to return a SmartContrast pointer everytime the Action is clicked. And that would still be possible to do it because of the inheritance from the class Effect. But I really can't figure out how to do that. Any help would be much appreciated. Thanks in advance!

Answer 1

Looks like QSignalMapper is exactly what you're looking for.
UPDATED:
Another way is to use lambda (if Qt version and c++ compiler allows):
QObject::connect(actionSmartContrast, &QAction::triggered, [effectsWindow](){ effectsWindow->addEffect(new SmartContrast()) });

Answer 2

There are several options.
If it is enough to have the base class pointer of the effects because you use e.g. virtual methods following solution should do:
You can create an intermedite class:
class Intermediate : public QObject
{
Q_OBJECT
public:
Intermediate(QObject* parent = 0) : QObject(parent){}
signals:
void triggerEffect(Effect*);
public slots:
void effectTriggered()
{
QAction* action = qobject_cast<QAction*>(QObject::sender());
if ( action ) {
std::map<QAction*,Effect*>::iterator it = m_mapping.find(action);
if ( it != m_mapping.end() )
{ emit triggerEffect( it->second ); }
}
}
public:
void registerActionEffectPair(QAction* action,Effect* effect)
{ m_mapping[action]=effect; }
private:
std::map<QAction*,Effect*> m_mapping;
};
To use your Effect base class as type for signals and slots, you have to register it as a metatype:
qRegisterMetaType<Effect*>();
Connect it:
QObject::connect(intermediateInstancePtr, SIGNAL(triggerEffect(Effect*),
effectsWindow, SLOT(addEffect(Effect*)));
And the connections of each action would look like:
intermediateInstancePtr->registerActionEffectPair( yourEffectAction, theEffectPtr );
QObject::connect(yourEffectAction, SIGNAL(triggered(bool)),
intermediateInstancePtr, SLOT(effectTriggered()));
Another one could be to use QObjects properties:
setProperty( "property", "value" )
Call this for each effect QAction and read the property in the slot "addEffect".
The property can be read by calling
QAction* action = qobject_cast<QAction*>(QObject::sender());
if ( action ){
QVariant val = action->property("property");
if ( val.isValid() )
{
//TODO
}
}
since Object::sender returns the sender which is responsible for the slot call.
Afterwards you can do a switch case or stuff like this to distinguish between the different effects.

Answer 3

I finally solved my problem! I subclassed QAction and added a signal to my new class which creates a new effect from the class I want depending on the property text(). Simple if blocks are enough. Thank you all for your answers!