Problems while using QPushButton

Eijin

Hi everyone, i'm having some trouble using QPushButton, what i'm trying to do is to create a Button that, once clicked, makes my slider "value" 150. Here is the code i wrote, but, this is still not working :)

@#include <QtGui/QApplication>
#include <QSlider>
#include <QPushButton>
#include <QHBoxLayout>
#include <QObject>

int main(int argc, char *argv[])
{

QApplication app(argc, argv);

QWidget *finestra= new QWidget;
finestra->setWindowTitle("Player");



QSlider *sli= new QSlider;
sli->setRange(0,150);



QPushButton *play= new QPushButton("Play");
QObject::connect(play, SIGNAL(clicked()), sli, SLOT(setValue(150)));

QHBoxLayout *lay= new QHBoxLayout;
lay->addWidget(sli);
lay->addWidget(play);
lay->addWidget(te);
finestra->setLayout(lay);
finestra->show();



return app.exec();

}
@

Any idea?:) Thanks for the attention :)

DenisKormalev

It of course will not work. Try to read "about signals and slots in Assitant":http://doc.qt.nokia.com/4.7/signalsandslots.html . It will help you to understand better that mechanism.

ZapB

You cannot assign arguments in a connect statement. Instead create a slot of your own and in that call sli->setValue( 150 ).

alexisdm

Or you can map the value 150 to the button with QButtonGroup, QSignalMapper or QStateMachine, if you want to stay a little while longer in the main function only.

leon.anavi

Check the simple example of "QPushButton at our wiki":http://developer.qt.nokia.com/wiki/How_to_Use_QPushButton. Follow the code snippet and modify method handleButton() to change the value of your slider.

rokemoon

@
#include <QtGui/QApplication>
#include <QSlider>
#include <QPushButton>
#include <QHBoxLayout>
#include <QObject>
#include <QSignalMapper>

int main(int argc, char *argv[])
{
QApplication app(argc, argv);

QWidget *finestra= new QWidget;
finestra->setWindowTitle("Player");

QSlider *sli= new QSlider;
sli->setRange(0,150);

QPushButton *play= new QPushButton("Play");

const int value = 150;
QSignalMapper signalMapper;
QObject::connect(play, SIGNAL(clicked()), &signalMapper, SLOT(map()));
signalMapper.setMapping(play, value);

QObject::connect(&signalMapper, SIGNAL(mapped(int)),
              sli, SLOT(setValue(int)));

QHBoxLayout *lay= new QHBoxLayout;
lay->addWidget(sli);
lay->addWidget(play);
finestra->setLayout(lay);
finestra->show();

return app.exec();

}
@

loladiro

For stuff like this I'm looking forward to lambda expressions with signal/slots in Qt5.

rokemoon

[quote author="loladiro" date="1313319918"]For stuff like this I'm looking forward to lambda expressions with signal/slots in Qt5.[/quote]
Hi loladiro, have you any examples of that?

loladiro

"This is currently being discussed to be merged into Qt5":http://developer.qt.nokia.com/wiki/New_Signal_Slot_Syntax
There's a link to the repository with the code in that article and there's also a merge request for it with qtbase.

And then stuff like this will be possible:
@
connect(sender, &Sender::valueChanged, [=](const QString &newValue) {
receiver->updateValue("senderValue", newValue);
} );
@
Or as is our example
@
QObject::connect(play, SIGNAL(clicked()), ={sli->setValue(150);});
@
THIS CODE IS NOT WORKING IN QT4, AND MIGHT NOT EVEN WORK IN QT5 AS THE SYNTAX IS SUBJECT TO CHANGE

rokemoon

[quote author="loladiro" date="1313320494"]"This is currently being discussed to be merged into Qt5":http://developer.qt.nokia.com/wiki/New_Signal_Slot_Syntax
There's a link to the repository with the code in that article and there's also a merge request for it with qtbase.

And then stuff like this will be possible:
@
connect(sender, &Sender::valueChanged, [=](const QString &newValue) {
receiver->updateValue("senderValue", newValue);
} );
@
Or as is our example
@
QObject::connect(play, SIGNAL(clicked()), ={sli->setValue(150);});
@
THIS CODE IS NOT WORKING IN QT4, AND MIGHT NOT EVEN WORK IN QT5 AS THE SYNTAX IS SUBJECT TO CHANGE[/quote]
Thanks, really impressive.