Sending static signals, is it possible?

plaktos

Is it possible to send a static signal?

I have a list of entry widgets inside a list and I want the container to be notified if one of them gets selected.
I don't want to connect all the entries idividually so I tought sending a static signal might work

public signals:
        static void SelectedStateChanged();

I connect it to the QCheckBox

connect(selectedCheckBox, &QCheckBox::stateChanged,
            [this](){
        emit SelectedStateChanged();
        });

Then in the list widget I connect to the static signal.
I have tried multiple ways:

Qt5 syntax:

// Connect the static signal from a dummy entry
    DeckScrollListEntry *dummyEntry = new DeckScrollListEntry(this);
    connect(dummyEntry, &DeckScrollListEntry::SelectedStateChanged,
            this, &DeckScrollList::refreshSelections);
    delete dummyEntry;

Compiler error:

error: no matching function for call to 'DeckScrollList::connect(DeckScrollListEntry*&, void (*)(), DeckScrollList*, void (DeckScrollList::*)())'
             this, &DeckScrollList::refreshSelections);

Macro syntax:

DeckScrollListEntry *dummyEntry = new DeckScrollListEntry(this);
    connect(dummyEntry, SIGNAL(SelectedStateChanged()),
            this, SLOT(refreshSelections));
    delete dummyEntry;

Compiler error:

error: 'this' is unavailable for static member functions
     QMetaObject::activate(this, &staticMetaObject, 1, nullptr);
                           ^

Is there any way or should I redesign and make connections for every entry.

sierdzio

Connections always relay on concrete object instances. It makes no sense for signal to be static, because signal has to come from a "living" object.

You are creating the DeckScrollListEntry objects somewhere, so connect the signals there, too. Alternatively, use automated connections: connectSlotsByName(). I don't recommend it, though, because it is very easy to make a mistake here. The new connection syntax is definitely the best.

plaktos

I'm not sure if you understood what I was trying to do. It wasn't really clear from what I posted.
Tough I have since realized that it's a horrible design that would lead to all kinds of bugs down the road.
What I was trying to do is something like this

connect(static signal &DeckScrollListEntry::SelectedStateChanged,
                    this, &DeckScrollList::refreshSelections)
)

So it would connect to a static signal that is sent by any DeckScrollListEntry.
So in a way it would connect to every DeckScrollListEntry.
And I also realized this is not possible of course, and it would be horrible if it were possible.

sierdzio

@plaktos said in Sending static signals, is it possible?:

So it would connect to a static signal that is sent by any DeckScrollListEntry.

I understood it exactly like that. It's not possible to do.

VRonin

Disclaimer

I'm not saying this is something you'd want to do

You can use a static/singleton QObject as the source of your signal