Query signal for value in lambda function

[Sewing]

I am trying to use the following syntax to propagate a signal up my widget hierarchy

  connect(imgSeqCtrl, &ImgSeqCtrlWidget::step,  [this]() {  emit mySignal(1);  });

where step is a signal with the following signature

void step(int);

Now, I want to emit a different signal depending on the sign of the step's signal value. Is there a possibility to query the steps actual value inside the lambda or is there now way around an additional dispatch function in which I do the case query?

[kshegunov]

What is the signature of ImgSeqCtrlWidget::step?

[t3685]

Yes, you need to change your lambda to:

[this](int value) { 
if (value < 0) 
    emit signal1(); 
else 
    emit signal2();
}

Basically the lambda needs to take the same (or less) arguments as your initial signal.

[Sewing]

thank you!

@kshegunov
void ImgSeqCtrlWidget::step(int);

[J.Hilk]

@Sewing Just to complete the picture, you don't need a Lambda to propagate a Sigal, you can connect Signals to Signals as long as the arguments are compatible, which theay are in your case:

connect(imgSeqCtrl, &ImgSeqCtrlWidget::step,  this, &myClassName::mySignal);

[Sewing]

Yes, but what if I want to send my signal, equipped with two different values?

[J.Hilk]

@Sewing well that depends, if you want to add a new argument to your Signal than you'll need a function to do that, that function can be an actual SLOT of your class or a lambda.

however droping arguments, no problem

//SignalA(int index, QString text);
//SignalB(int index);

//This os ok
connect(objectA, &&QObject::SignalA, objectB, &QObject::SignalB);

//This is not
connect(objectB, &&QObject::SignalB, objectA, &QObject::SignalA);

//Howver iirc this should work:
//SignalA(int index, QString text = "DefaultText");
//SignalB(int index);
connect(objectB, SIGNAL(SignalB(int)), objectA, SIGNAL(SignalA(int,QString)));

[Sewing]

thank you!