Signal and Slot

kamejoko

how to connect signal and slot? Sorry so my english is not good. I want to understand how the signal and slot can connect together.

Chris Kawa

Hi, see Signals & Slots in the documentation for detailed explanation.

Emre MUTLU

QObject::connect(SignalSender,SIGNAL(yoursignal),SignalReceiver,SLOT(yourslot));

ex:

MainWindow w;
myClass myObj;
QObject::connect(&w,SIGNAL(someSignal),&myObj,SLOT(someSlotinMyClass);

if you use pointer then don't necessary '&'

jsulm

@Emre-MUTLU It is better to use newer Qt5 connect syntax as it gives you compile time errors if you do something wrong instead of runtime errors.

Emre MUTLU

connect(sender, &sender::Signal, this, &MyObj::someSLOT);

like this right ?

jsulm

@Emre-MUTLU said in Signal and Slot:

connect(sender, &sender::Signal, this, &MyObj::someSLOT);

Almost:

connect(sender, &SenderClass::Signal, this, &MyObj::someSLOT);

Emre MUTLU

This post is deleted!

kamejoko

sorry, i don't ask the syntax of signal and slot. I want to understand meta-object compiler. Signal and slot are macros and they are connected by meta-object, right?

JKSH

@kamejoko said in Signal and Slot:

I want to understand meta-object compiler. Signal and slot are macros and they are connected by meta-object, right?

You can start here: https://woboq.com/blog/how-qt-signals-slots-work.html (at the end of this article, there is a link to Part 2)

jsulm

@kamejoko said in Signal and Slot:

Signal and slot are macros

No, they are methods. Slot is written by programmer. Signal is generated for you by moc and you can see how it is implemented by looking into generated header file. QObject::connect just memorises that the slot needs to be called when the signal is called.

kamejoko

@JKSH thank you about that!

kamejoko

@jsulm thanks. that's exactly is which i want to know. Could you tell me how many type of signal and slots mechanism? I read at doc.qi.io and i see there are two signal and slots mechanism. One is "Signals and slots with default argument". Two is "Advance signals and slots Usage". I don't know whether i'm true

jsulm

@kamejoko said in Signal and Slot:

Could you tell me how many type of signal and slots mechanism?

I'm not sure what you're asking.
There is only one type of signals/slots, but two different ways to connect them:

The old connect syntax using SIGNAL and SLOT macros
The newer and better connect syntax using function pointers

Signals and slots can have 0..n parameters, like any other function/method.

kamejoko

@jsulm ok. thank you very much. My question is solved!