Question

Possible Duplicate:
Using QSlider to change the value of a variable

I’m trying to use the QSlider to to change a variable value:
here is a part of the code :

 ....
QSlider *slider = new QSlider(Qt::Horizontal,0);
connect(slider,SIGNAL(valueChanged()),this,SLOT(value(int k)));
...

the function value is a SLOT that I want to use let’s say like this:

 void value (int k ) {
cout<< k << endl;
}

the problem that I have is that nothing happens when I move the slider. ?

thanks in advance

Answer 1

You have to put the argument int on the signal signature to make it pass the value to the slot. Also, never put argument names in the SIGNAL(...) / SLOT(...) signature specifications.

...
QSlider *slider = new QSlider(Qt::Horizontal, this);
connect(slider, SIGNAL(valueChanged(int)), this, SLOT(value(int)));
...

Also, make sure that value is a slot of your class, not a free-standing function. I guess you already put the code above in a class function, not in main or any other free-standing function, because in these there is no this defined. So the slot you are talking about has to be a member function, especially a QObject slot of the class you are writing this code in. Change

void value (int k) {
    cout << k << endl;
}

to

void MyClass::value (int k) {
    cout << k << endl;
}

and in your class definition of MyClass add a public slots: section:

class MyClass : public ... {
    Q_OBJECT
    ...
public slots:
    void value(int);
    ...
}

Also, give your slot a meaningful name, for example sliderChanged, otherwise, chaos will rule your project sooner or later for sure.