Automatic connection of QML signal and C++ slot?

Tom asso

Automatic connection of QtWidgets and C++ application code saves lots of development time. Is there a similar automatic connection feature for QML/QtQuick signals and application code, or do I have write my own calls to QObject::connect() for every QML Item that my C++ application code is concerned with? If automatic connection is not supported for this, why not?
Thanks!

Axel Spoerl

@Tom-asso said in Automatic connection of QML signal and C++ slot?:

But are there cases where QML signal to C++ slot makes sense? Maybe in the case of one QML emitter and multiple C++ 'listeners'?

It’s better to call a C++ function from QML and do the plumbing in C++, I wouldn’t know of a use case where such connections are the best possible solution.

Axel Spoerl

@Tom-asso
Yes in the sense that every binding is an automatic signal/slot connection.
No in the sense, that functional slots have to be explicitly connected. The syntax is quite simple, so I wouldn’t even call that a downside.

Tom asso

@Axel-Spoerl Design question for you:
If my C++ app must respond to multiple menu actions, e.g. 10 actions, then my C++ code must do the following, right?

declare/define 10 slot functions
make 10 calls to connect(), once for each slot declared in step 1

That's the gist of it, right? Those 10 connect() calls just seem like a lot of application code to a lazy sob like me. ;-) Or is there an easier way to do it?
Do qtcreator or qtdesignstudio offer a more 'automatic' way?
Thanks!

GrecKo

@Tom-asso you usually don't connect to QML signals in c++. What you should do is expose your c++ slots and type/objects and call them in QML.

onClicked: myCppObject.doStuff()

Axel Spoerl

@Tom-asso said in Automatic connection of QML signal and C++ slot?:

If my C++ app must respond to multiple menu actions, e.g. 10 actions, then my C++ code must do the following, right?

declare/define 10 slot functions

make 10 calls to connect(), once for each slot declared in step 1

That's the gist of it, right?

Yes.

Those 10 connect() calls just seem like a lot

yy9pis the sequence in vim, doing 80% of this job for you. The rest is usually about editing a few letters :-)

You can of course use autoconnect - totally fine, it has been designed for the comfort you are seeking.
The caveat is, that a mismatch of a single character will leave signal/slot unconnected without notice.
Depending on an exact string match in an XML file and C++ code, comes particularly unhandy when searching for a bug. I have seen furious forum posts and bugreports about QObject::connect()allegedly not working properly. I remember a project from a few years ago, where a company's quality department has done a huge effort in renaming_all_underline_stuff intoCamelStyle, autoconnected slots included. Compiled like a charm, and set the UI on fire.

J.Hilk

@Tom-asso don't use that feature if you can help yourself!

These days there's Ai/copilot to do repetitive boring and simple tasks. Like creating slots for signals or unit tests for functions.

Rather use that.

JonB

@J-Hilk said in Automatic connection of QML signal and C++ slot?:

These days there's Ai/copilot to do repetitive boring and simple tasks.

Nothing will ever equate to the efficiency and clarity of @Axel-Spoerl's yy9p in vim ;-)

J.Hilk

@JonB I actually have no idea what it is :P first time I heard about it.

But just wait until Ai is part of your OS and always listening, like Alexa....

Not a disturbing thought at all.

JonB

@J-Hilk If you don't know what yy9p does in vi your life is lacking. Surely it's clear what it does anyway... ;)

J.Hilk

@JonB so I asked chatgpt :P so I now know!

and I also generally try not to use a cmd line text editor if I can help it ;)

GrecKo

I'm sorry but do not connect to QML signals in c++, even though it's simple with some editor magic (Qt Creator ctrl-d is much easier to grok than vim bindings btw). You will still be left with verbose and subpar code.

https://doc.qt.io/qt-5/qtquick-bestpractices.html#interacting-with-qml-from-c
https://doc.qt.io/qt-6/qtquick-bestpractices.html#exposing-data-from-c-to-qml
https://doc.qt.io/qt-6/qtqml-cppintegration-overview.html#interacting-with-qml-objects-from-c
https://youtu.be/vzs5VPTf4QQ?t=23m20s

Tom asso

@Axel-Spoerl autoconnect is only for Qt-Widgets, not enabled for QtQuick/QML, correct?

Tom asso

@GrecKo - Thanks for those references! I think I generally agree with you now (after I wrote my entire freaking C++ app using signals/slots!). But are there cases where QML signal to C++ slot makes sense? Maybe in the case of one QML emitter and multiple C++ 'listeners'?

Axel Spoerl

@Tom-asso said in Automatic connection of QML signal and C++ slot?:

But are there cases where QML signal to C++ slot makes sense? Maybe in the case of one QML emitter and multiple C++ 'listeners'?

It’s better to call a C++ function from QML and do the plumbing in C++, I wouldn’t know of a use case where such connections are the best possible solution.

SimonSchroeder

@J-Hilk said in Automatic connection of QML signal and C++ slot?:

I also generally try not to use a cmd line text editor if I can help it ;)

There also graphical versions of vi. And Qt Creator supports FakeVim which you can quickly toggle.

JonB

@SimonSchroeder I think @J-Hilk's interest in using vi/vim in any shape or form is absolute 0! We were jesting back & forth.