Passing an argument to a slot

Question

I want to override mouseReleaseEvent with a bunch of QActions and QMenus ...

connect(action1, SIGNAL(triggered()), this, SLOT(onStepIncreased())); connect(action5, SIGNAL(triggered()), this, SLOT(onStepIncreased())); connect(action10, SIGNAL(triggered()), this, SLOT(onStepIncreased())); connect(action25, SIGNAL(triggered()), this, SLOT(onStepIncreased())); connect(action50, SIGNAL(triggered()), this, SLOT(onStepIncreased())); 

So, I want to pass an argument to the onStepIncreased slot (as you can imagine, this is 1,5,10,25,50). Do you know how I can do this?

Answer 1

Use QSignalMapper . Like this:

 QSignalMapper* signalMapper = new QSignalMapper (this) ; connect (action1, SIGNAL(triggered()), signalMapper, SLOT(map())) ; connect (action5, SIGNAL(triggered()), signalMapper, SLOT(map())) ; connect (action10, SIGNAL(triggered()), signalMapper, SLOT(map())) ; connect (action25, SIGNAL(triggered()), signalMapper, SLOT(map())) ; connect (action50, SIGNAL(triggered()), signalMapper, SLOT(map())) ; signalMapper -> setMapping (action1, 1) ; signalMapper -> setMapping (action5, 5) ; signalMapper -> setMapping (action10, 10) ; signalMapper -> setMapping (action25, 25) ; signalMapper -> setMapping (action50, 50) ; connect (signalMapper, SIGNAL(mapped(int)), this, SLOT(onStepIncreased(int))) ; 

Answer 2

With Qt 5 and the C ++ 11 compiler, the idiomatic way to do such things is to give the functor a connect :

 connect(action1, &QAction::triggered, this, [this]{ onStepIncreased(1); }); connect(action5, &QAction::triggered, this, [this]{ onStepIncreased(5); }); connect(action10, &QAction::triggered, this, [this]{ onStepIncreased(10); }); connect(action25, &QAction::triggered, this, [this]{ onStepIncreased(25); }); connect(action50, &QAction::triggered, this, [this]{ onStepIncreased(50); }); 

The third argument to connect nominally optional. It is used to set the context of the stream in which the functor will be executed. This is always necessary when a functor uses an instance of QObject . If a functor uses multiple instances of QObject , they must have some common parent that controls their lifetime, and the functor must reference this parent or must ensure that objects overflow the functor.

On Windows, this works on MSVC2012 and later.

Answer 3

The QObject::sender() function returns a pointer to the object that signaled the slot. You can use this to find out what action was triggered.

Answer 4

Perhaps you can subclass QAction with the m_increase member variable.
Connect the trigger signal () to the slot in the new QAction subclass and emit a new signal (e.g., triggered (int number)) with the correct parameter.
eg

 class MyAction:public QAction { public: MyAction(int increase, ...) :QAction(...), m_increase(increase) { connect(this, SIGNAL(triggered()), this, SLOT(onTriggered())); } protected Q_SLOTS: void onTriggered() { emit triggered(m_increase); } Q_SIGNALS: void triggered(int increase); private: int m_increase; }; 

Answer 5

 QVector<QAction*> W(100); W[1]= action1; W[5]= action5; W[10]= action10; W[25]= action25; W[50]= action50; for (int i=0; i<100; ++i) { QSignalMapper* signalmapper = new QSignalMapper(); connect (W[i], SIGNAL(triggered()), signalmapper, SLOT(map())) ; signalmapper ->setMapping (W[i], i); connect (signalmapper , SIGNAL(mapped(int)), this, SLOT(onStepIncreased(int))); }