Questions about slots

saxoalex

Hi ! I'm sorry, in advance, for my bad english.

I'm trying to run a program which use slots. Compilation works but when I run the program, he wait and don't do anything.

Here we have the function :

void Fenetre::Commencer()
{
    main_display->setText("Bienvenue dans jhqqjhfqjf, le nouveau jeu video de la mort qui tue !\n");
    boutons[0]->setText("Commencer");
    boutons[1]->setText("Quitter ? Deja ?");
    boutons[2]->setText("Bouton vers la victoire");
    boutons[2]->setEnabled(false); //Parce que c'est marrant

    connect(boutons[0], SIGNAL(pressed()), this, SLOT(Etape(0,0)));
    connect(boutons[1], SIGNAL(pressed()), this, SLOT(reject()));
}

And his declaration on my class :

public slots:
    void Etape(int from, int to);

Can I put arguments in a slot ?
Thank's !
Alexandre.

JKSH

Hi @saxoalex, and welcome!

@saxoalex said in Questions about slots:

Can I put arguments in a slot ?

No. A slot can only get arguments from the signal.

connect(boutons[0], SIGNAL(pressed()), this, SLOT(Etape(0,0)));

This connection is wrong because:

The pressed() signal has no arguments, so it can only be connected to slots that also have no arguments.
You cannot write values/numbers in the connection. You can only write data types (such as "bool", "int", or "QString"). Example:
- connect(slider, SIGNAL(valueChanged(int)), spinbox, SLOT(setValue(int))); // slider is a QSlider, spinbox is a QSpinBox

connect(boutons[1], SIGNAL(pressed()), this, SLOT(reject()));

This connection is OK.

Compilation works but when I run the program, he wait and don't do anything.

First, please read http://doc.qt.io/qt-5/signalsandslots-syntaxes.html

You are using String-based connections, so your compiler cannot check them. You can change to Functor-based signals and let your compiler do the checks.

// OK
connect(boutons[1], &QPushButton::pressed,
        this, &Fenetre::reject);

// Compiler error. The signal and slot are not compatible
connect(boutons[0], &QPushButton::pressed,
        this, &Fenetre::Etape);

// OK -- using a Lambda Expression
connect(boutons[0], &QPushButton::pressed, [this] {
    this->Etape(0,0);
});

saxoalex

It work ! I understand.

Thank you very much for this information !