Qt connect() without QObject or slots

Question

I know what I am trying to achieve is possible, because I can do it with a lambda expression and I have done it before (Few months ago I just don't remember the syntax). Basically, I want to connect a function to a timer/button/etc. to facilitate the workings of an event.

Here is my working code:

connect( &renderTimer, &QTimer::timeout, [ = ]() {
        onTimerUpdate();
    } );

That uses a lambda to connect to the slot. I want to just reference the function itself instead of using a lambda expression. I have tried inserting the method onTimerUpdate() and &onTimerUpdate none of which work. I don't want to use QObject or any of it's pre-generated bullcrap — nor do I want to define slots within my class. I want to, quite simply, connect it directly to my function.

Answer 1

This is the format when connecting to a member function:

QObject::connect(&renderTimer, &QTimer::timeout, this, &ArclightGLWidget::onTimerUpdate); 

This is the format when connecting to a free funciton (same for lambda)

QObject::connect(&renderTimer, &QTimer::timeout, onTimerUpdate); 

And this is the format when connecting to a static member function:

QObject::connect(&renderTimer, &QTimer::timeout, SomeType::onTimerUpdate); 

Answer 2

Presumably this call is being made inside the class of which onTimerUpdate is a method. If so you can call:

connect(&renderTimer, &QTimer::timeout, this, &foo::onTimerUpdate); 

This is preferable to the lambda because Qt will manage the connection and you will also be able to call sender() in the slot.

However if you are within the class in which onTimerUpdate is a method you can also use the lambda exactly as you have put in the question:

connect( &renderTimer, &QTimer::timeout, [=](){onTimerUpdate();} );