QListWidget, how to post a question to the user before allowing change?

[jsulm]

@SPlatten You don't have to use emit.
emit is an empty macro and is only used to make clear to the reader of the code that a signal is emitted.
Also, trying to execute the code is faster than asking in a forum and waiting for an answer :-)

[J.Hilk]

@SPlatten emit ist syntactic sugar, it expands to void. askSelect is a simple function, that has it function body in the *moc file that qmake creates.

but, yes you can add it :D

[SPlatten]

@VRonin , can you help with this implementation?

//ABC = Ask Before Change
QString strABC(mpobjNode->strGetAttribute
                                (clsXMLnode::mscszAttrAskBeforeChange));
if ( strABC.isEmpty() != true ) {
//Use "clsQtAskBeforeChange" to prompt user for confirmation if
//changes in child nodes before allowing change
    clsQtAskBeforeChange* pobjABC(new clsQtAskBeforeChange(model(), this));
    setSelectionMode(QAbstractItemView::ExtendedSelection);
    setSelectionModel(pobjABC);
//Now the widget should be set-up, finalise set-up
    clsXMLinterface::setup();
//Connect signal
    clsQtListWidget* pobjThis(this);
    QObject::connect(pobjABC, &clsQtAskBeforeChange::pendingSelect
                ,[pobjABC, strABC, pobjThis](const QItemSelection& crobjSelection
                    ,QItemSelectionModel::SelectionFlags cmdFlags) {
        if ( QMessageBox::question(pobjThis, QStringLiteral("Please confirm...")
                , strABC) == QMessageBox::StandardButton::Yes) {
            pobjABC->actuallySelect(crobjSelection, cmdFlags);
        }
    });
}

The above is in my implementation of QListWidget constructor. On the line that contains:

QObject::connect(pobjABC, &clsQtAskBeforeChange::pendingSelect

To the right of it I have the message:

Pass a context object as 3rd connect parameter [clazy-connect-3arg-lambda]

This is cryptic, I don't understand what it is telling me, have I done anything wrong because the code seems to work fine?

[JonB]

@SPlatten
Although this 3-argument connect() works, it is more usual to pass 4 arguments, with the 3rd argument being the "context" object for the slot's this. That is what the warning is telling you. I believe you can get rid of that via (something like):

    QObject::connect(pobjABC, &clsQtAskBeforeChange::pendingSelect
                , pobjABC, [strABC, pobjThis](const QItemSelection& crobjSelection
                    ,QItemSelectionModel::SelectionFlags cmdFlags) {
        if ( QMessageBox::question(pobjThis, QStringLiteral("Please confirm...")
                , strABC) == QMessageBox::StandardButton::Yes) {
            this->actuallySelect(crobjSelection, cmdFlags);
        }
    });

[Christian Ehrlicher]

@JonB Since the lambda accesses this, the third parameter should be this too. Otherwise the disconnect will not be done when this is deleted but pobjABC is still alive.

[JonB]

@Christian-Ehrlicher
I'm lost --- where does the (original) lambda access this? The only this is the one I put in for the pobjABC which I have made the context? In the body I replaced pobjABC->actuallySelect() by this->actuallySelect(), for clarity; and I chose pobjABC as the context as it felt like that was the primary slot object there. (I did get this right, didn't I? The slot-context-object, my pobjABC, becomes this in the lambda body?) My thought was to pass that as it won't be disconnected if pobjABC dies. I admit I didn't look terribly closely, I get awfully mixed with all the OP's pobj...s :)

[Christian Ehrlicher]

@JonB I only looked at your answer - the slot accesses this and not pobjABC so the signals scope should be this too :)

[SPlatten]

@JonB , pobjABC does become this in the lambda because the connection is created using pobjABC.

I've tried various suggestions, however I'm still getting the same result:

Pass a context object or 3rd connect parameter [clazy-connect-3ard-lambda]

This is gibberish because there are already 3 parameters passed. I even changed the parameters to:

[strABC, pobjABC, this, pobjThis]

Still get the same message.

[Christian Ehrlicher]

@SPlatten said in QListWidget, how to post a question to the user before allowing change?:

This is gibberish because there are already 3 parameters passed.

This is not gibberish - you only have to read it properly and our answers... you have to pass a context as third parameter, not the lambda (this should be the forth then)

[JonB]

@SPlatten
I posted mine with a 4th parameter and explained. Did you actually copy it and get the same error message? I don't think so. The issue is the number of parameters to connect(). You are looking at the number of items in the [...] context for the lambda, which is not what the message refers to.

[SPlatten]

@JonB , @Christian-Ehrlicher , sorry, it wasn't clear to me at first that the actual 3rd parameter you were referring to was of the connect, I thought it was the 3rd parameter of the lambda set.

It was more confusing because when compiled the connect worked without the 3rd parameter. being correct.

[JonB]

@SPlatten
Your 3-parameter one should work, the [clazy-connect-3arg-lambda] should be a warning that it can be inadvisable because of lifetime/disconnect behaviour.