Cannot pass parameter in SLOT

GunkutA

Hello, I am trying to declare an action in Custom menu Request as:

void protocolForm::customMenuRequested(QPoint pos)
{
    QMenu *menu = new QMenu(this);
    menu->addAction(enumArray.value(0),this,SLOT((sendEnumSlot(0))));
    menu->addAction(enumArray.value(0),this,SLOT((sendEnumSlot(1))));
    menu->addAction(enumArray.value(0),this,SLOT((sendEnumSlot(2))));
    menu->addAction(enumArray.value(0),this,SLOT((sendEnumSlot(3))));
    menu->addAction(enumArray.value(0),this,SLOT((sendEnumSlot(4))));
    menu->addAction(enumArray.value(0),this,SLOT((sendEnumSlot(5))));
}

enumArray is Qstring vector. When I try that in this way with integer parameter in sendEnumSlot() slot, that gives me

QObject::connect: (receiver name: 'widget')
QObject::connect: No such slot protocolForm::sendEnumSlot(0)
warnings

However when I try the same thing with declaring the sendEnumSlot() without any parameters in it and add action as:

void protocolForm::customMenuRequested(QPoint pos)
{
    QMenu *menu = new QMenu(this);
    menu->addAction(enumArray.value(0),this,SLOT((sendEnumSlot()));
    menu->addAction(enumArray.value(1),this,SLOT((sendEnumSlot()));
    menu->addAction(enumArray.value(2),this,SLOT((sendEnumSlot()));
    menu->addAction(enumArray.value(3),this,SLOT((sendEnumSlot()));
   menu->addAction(enumArray.value(4),this,SLOT((sendEnumSlot()));
   menu->addAction(enumArray.value(5),this,SLOT((sendEnumSlot()));
}

That works. Am I missing something? How can I overcome this problem?

sierdzio

Signal-slot connections are between methods. You cannot specify concrete values for slot parameters - these are always taken from the signal.

If you want to call the same slot with different value based on menu item, you can:

connect your action to lambda and call your slot with correct parameter inside
or call the same slot from all actions, but in the slot call sender() and infer which action triggered the call
or create separate slots for each of your actions

GunkutA

@sierdzio How can I use sender() function? That returns some address value I guess. How can I know which action refers to that address value?

sierdzio

auto action = qobject_cast<QAction*>(sender());
if (action) {
  if (action->text() == enumArray.value(0)) {
    // First action triggered the slot
  }
}

GunkutA

@sierdzio Thanks

SimonSchroeder

@sierdzio There is a fourth option to provide a value to the slot: Qt has a helper class calls QSignalMapper. Haven't used it ever, though ;-)