qt - 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 slot onStepIncreased (as you can imagine they are 1,5,10,25,50). Do you know how I can do it?

Answer 1

With Qt 5 and a C++11 compiler, the idiomatic way to do such things is to give a functor to 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 is nominally optional. It is used to set up the thread context in which the functor will execute. It is always necessary when the functor uses a QObject instance. If the functor uses multiple QObject instances, they should have some common parent that manages their lifetime and the functor should refer to that parent, or it should be ensured that the objects will outlive the functor.

On Windows, this works in MSVC2012 & newer.