Connect Dynamically created Sliders and Labels (Solved)

hypnomaki

Im creating QSliders and QLabels in my Program and i want to connect them so when I'm changing the Slider the Value should be shown within the label.

So i thought about something like this

@
Qlabel label;
QSlider silder;
connect(slider, SIGNAL(valueChanged(int)), this, ChangeText(slider, label));

void ChangeText(&slider, &label)
{
label.setText(Slider.Value);
}@

but this wont work.
The Compiler tells me "invalid use of void expression"

SGaist

Hi,

There are several things that are wrong with your code:
Your ChangeText function signature is invalid
Your connect statement is wrong.
If you have put that code as is in a cpp file then it won't even compile

You should check the "Signals And Slots":http://doc.qt.io/qt-5/signalsandslots.html chapter of Qt's documentation

Rondog

I am not aware of any way to pass a pointer of the widget when the slot is called. There might be but I am not aware of it.

If you have only a few slider-label combinations you could have a slot for each. Example:
@
change_text_slider1(int){;}
change_text_slider2(int){;}
// etc.
@

You could create a subclass of the slider. With a subclass you can emit your own signals (which can include a pointer or some other identifying information).

@
void MySlider::value_changed(int value)
{
int id=(identifier, maybe pointer,?);

emit Value_Changed(id, value);
}
@

SGaist

"QSignalMapper":http://doc.qt.io/qt-5/qsignalmapper.html would probably help for that purpose

Rondog

Thanks SGaist. Although this is not my thread I wasn't aware of QSignalMapper. Learned something new.

hypnomaki

Rondog, I cant create So many Slots because i dont know how many sliders are going to be created.

SGaist, this looks good, I just had a look at it but its not as easy.
I tried:
@
QSlider *slider;
QLabel *label;
QSignalMapper *mapper = new QSignalMapper(this);
connect(slider, SIGNAL(valueChanged(int)), mapper, SIGNAL(mapped(int)));
connect(mapper,SIGNAL(mapped(int)),this,SIGNAL(LabelSlider(label,slider)));
@
@
void Dashboard::LabelSlider(QLabel *label, QSlider *slider)
{
label->setText(QString::number(slider->value()));
}
@
Its compiling but it doesnt work. What am I doing wrong?

Rondog

From what I read it looks like you need to do something like this:

@
signalMapper = new QSignalMapper(this);
...
connect(slider, SIGNAL(valueChanged(int)), signalMapper, SLOT(map()));
signalMapper->setMapping(slider, slider); // not sure?
...
connect(signalMapper, SIGNAL(mapped(QSlider*)),this, SLOT(value_changed(QSlider*)));

...

void Dashboard::value_changed(QSlider *slider)
{
label->setText(QString::number(slider->value()));
}

@

SGaist

Not exactly no. You can't modify signal/slots signature like that.

@
signalMapper = new QSignalMapper(this);
connect(slider, SIGNAL(valueChanged(int)), signalMapper, SLOT(map()));
signalMapper->setMapping(slider, label);
connect(signalMapper, SIGNAL(mapped(QWidget*)),this, SLOT(onMapped(QWidget*)));

void Dashboard:: onMapped(QWidget *widget)
{
QSlider slider = qobject_cast<QSlider>(signalMapper->mapping(widget));
QLabel label = qobject_cast<QLabel>(widget);
if (label && slider) {
label->setText(QString::number(slider->value()));
}
}
@

Rondog

I was close I guess (hope that counts for something - lol).

This opens up a few possiblities for me. I had problems like this in the past and never realized this class existed. It can make a few things easier.

hypnomaki

thx SGaist that acutally works!

SGaist

Well, I try not to post buggy code ;)

Since it's all working now, please update the thread title prepending [solved] so other forum users may know a solution has been found :)