error connecting signal to slot in custom class

Deneguil

Hello, I am trying to connect a signal between a series in a custom chart class to a slot in said chart class like so:

connect(series, SIGNAL(clicked(QPointF)), chart4Map, SLOT(pointClicked(QPointF)));

mapChart

class mapChart : public QChart
{
public slots:
    void pointClicked(const QPointF &point);
};

However when I do so I get the error QObject::connect: No such slot QtCharts::QChart::pointClicked(QPointF) which I don't understand as my chart4Map is a mapChart instance

JonB

@Deneguil
Since your slot signature parameter is const QPointF &point it won't match the plain QPointF in your SLOT().

Why don't you use "new" (actually very old now!) signal/slot syntax, instead of SIGNAL/SLOT(), it gives more help on these errors?

ChrisW67

The mapChart class presented is lacking a Q_OBJECT macro.
Also, have you ensured that moc has run over the header declaring mapChart?

J.Hilk

@Deneguil you're using old(Qt4) signal slot syntax, so your class 100% requires Q_OBJECT macro to work.

It is missing.

JonB

@ChrisW67 said in error connecting signal to slot in custom class:

The mapChart class presented is lacking a Q_OBJECT macro.

This is true, but as far as I know Q_OBJECT is not required for slots, only for signals?

Am I not right that the QPointF will not match const QPointF &point, and that is the error here? [UPDATE Oh, @J-Hilk says Qt4 will match these similar-but-different signatures, so maybe I am wrong, and it is indeed somehow the Q_OBJECT missing for Qt4, sorry if my attempts at answering have been wrong, I have learned something about Qt4 now! See also https://forum.qt.io/topic/115188/do-i-need-to-use-the-q_object-macro-if-i-only-use-slots]

@J-Hilk said in error connecting signal to slot in custom class:

@Deneguil you're using old(Qt4) signal slot syntax, so your class 100% requires Q_OBJECT macro to work.

Ah, I did not know that requirement! I don't think it's mandatory for a slot in new style, at least? One more reason for using new-style if not bound to Qt4!

J.Hilk

@JonB said in error connecting signal to slot in custom class:

I don't think it's mandatory for a slot in new style, at least?

you would be correct, the class containing the signal still requires it (I think)

Deneguil

@JonB said in error connecting signal to slot in custom class:

Since your slot signature parameter is const QPointF &point it won't match the plain QPointF in your SLOT().

I tried fixing the slot signature and adding the Q_OBJECT macro to my class as well and this time I got QObject::connect: No such signal QtCharts::QScatterSeries::clicked(const QPointF &point) which seems weird to me since ScatterSeries should have the signal inhearited from XYSeries.

Why don't you use "new" (actually very old now!) signal/slot syntax, instead of SIGNAL/SLOT(), it gives more help on these errors?

There was no other reason than I'm pretty new to Qt development and so far that was the syntax that worked for me so I didn't see a reason to change.
However after changing it to connect(series, &QScatterSeries::clicked, chart4Map, &mapChart::pointClicked); it works now so I'm probably going to change every SIGNAL()/SLOT() in my code now too

Thank you all for your help

JonB

@Deneguil said in error connecting signal to slot in custom class:

However after changing it to connect(series, &QScatterSeries::clicked, chart4Map, &mapChart::pointClicked); it works now so I'm probably going to change every SIGNAL()/SLOT() in my code now too

:) :) New style was introduced years & years ago. I know some old examples still use SIGNAL/SLOT(), but assuming you are Qt5 onward you are really a lot better off with new style!