QTimer: Getting Started problems

jastmc

I am a beginner, trying to get a QTimer to drive a simple counter. It should count up in seconds but the slot never gets called. What am I doing wrong? I want the timer to increment the state every second so its displayed on the screen.

This is my program:-

@#include "mita_screen.h"
#include "ui_mita_screen.h"

mita_screen::mita_screen(QWidget *parent) :
QDialog(parent),
ui(new Ui::mita_screen)
{
mita_screen::setWindowFlags(Qt::SplashScreen);
ui->setupUi(this);

mita_state = 0;     // Initialise the state machine

QTimer *timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), this, SLOT(state_update));
timer->start(1000);

}

mita_screen::~mita_screen()
{
delete ui;
}

void mita_screen::state_update()
{
mita_state++;

}

void mita_screen::paintEvent(QPaintEvent *)
{
QString data;

data = QString("%1")
        .arg(mita_state);

ui->label->setText(data);

}

void mita_screen::on_pushButton_clicked()
{
delete ui;
}
@

This is my main:-

@#include "mita_screen.h"
#include <QApplication>

int main(int argc, char *argv[])
{
QApplication a(argc, argv);
mita_screen w;
w.show();

return a.exec&#40;&#41;;

}
@

This is my header:-

@#ifndef MITA_SCREEN_H
#define MITA_SCREEN_H

#include <QDialog>
#include <QtGui>

namespace Ui {
class mita_screen;
}

class mita_screen : public QDialog
{
Q_OBJECT

public:
explicit mita_screen(QWidget *parent = 0);
~mita_screen();
int mita_state;

protected:
void paintEvent(QPaintEvent *event);

private slots:
void on_pushButton_clicked();
void state_update();

private:
Ui::mita_screen *ui;
};
#endif // MITA_SCREEN_H
@

bodzio131

I'm not sure you can omit brackets for slot state_update, probably should be:
@
connect( timer, SIGNAL( timeout() ), this, SLOT( state_update() ) );
@

Instead of QTimer you could also use QDialog::startTimer and virtual QDialog::timerEvent.

SGaist

Hi,

Remove the paintEvent, you are not painting anything.

@
void mita_screen::state_update()
{
ui->label->setText(QString("%1").arg(++mita_state));
}@

Is enough to update the label at on your timer's time out.

Why do you delete your ui variable in on_pushButton_clicked ? Also note, that it's already deleted in the destructor, so calling that function, then the destructor will cause a crash.

If you want to close the dialog, connect the pushButton clicked signal on the close slot of the dialog.

Hope it helps

raven-worx

change your connect-statement to:
@connect(timer, SIGNAL(timeout()), this, SLOT(state_update()));@

Edit: nvm ... too late :)

tomma

You just increment mita_state but never update it to screen.
Remove your "paintEvent":http://qt-project.org/doc/qt-4.8/qwidget.html#paintEvent implementation, which is all wrong, and update label text in state_update().

Also your connect call in line 14 should be @connect(timer, SIGNAL(timeout()), this, SLOT(state_update()));@

sierdzio

Slot connection is probably wrong

No need to reimplement the paint event

This should work:
@
mita_screen::mita_screen(QWidget *parent) :
QDialog(parent),
ui(new Ui::mita_screen)
{
mita_screen::setWindowFlags(Qt::SplashScreen);
ui->setupUi(this);

mita_state = 0;     // Initialise the state machine

QTimer *timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), this, SLOT(state_update()));
timer->start(1000);

}

void mita_screen::state_update()
{
mita_state++;
ui->label->setText(QString::number(mita_state));

}
@

sierdzio

Wow, we really flooded the poor guy :)

raven-worx

[quote author="sierdzio" date="1366112776"]Wow, we really flooded the poor guy :)[/quote]

yep...within 3 mins ... lol

SGaist

[quote author="sierdzio" date="1366112776"]Wow, we really flooded the poor guy :)[/quote]

Like one other user said, we're parallelizing :D

sierdzio

Yeah, but it would be a tad better to spread across different threads (pun well intended :)).

jastmc

Hey, don't knock it!

Its much better to get too many responses that none at all.

Thanks for all your help!

James

jastmc

SGaist said:-

bq. Why do you delete your ui variable in on_pushButton_clicked ? Also note, that it’s already deleted in the destructor, so calling that function, then the destructor will cause a crash.
If you want to close the dialog, connect the pushButton clicked signal on the close slot of the dialog.

I changed my code to connect the on_pushButton_clicked() signal to the ~mita_screen() slot but the button has no effect when pressed. See below.

Can anyone please tell me whats wrong here?

@#include "mita_screen.h"
#include "ui_mita_screen.h"

mita_screen::mita_screen(QWidget *parent) :
QDialog(parent),
ui(new Ui::mita_screen)
{
mita_screen::setWindowFlags(Qt::SplashScreen);
ui->setupUi(this);

mita_state = 0;     // Initialise the state machine

QTimer *timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), this, SLOT(state_update()));
timer->start(1000);

connect(ui->pushButton, SIGNAL(on_pushButton_clicked()), this, SLOT(~mita_screen()));

}

mita_screen::~mita_screen()
{
delete ui;
}

void mita_screen::state_update()
{
ui->label->setText(QString("%1").arg(++mita_state));

}

void mita_screen::on_pushButton_clicked()
{

}

void mita_screen::on_pushButton_pressed()
{

}
@

SGaist

You're connecting to the destructor:

1.It's not a slot
2.Never call a destructor, it's done for you when the object is destroyed.

As I said, connect to the "close slot":http://qt-project.org/doc/qt-4.8/qwidget.html#close

raven-worx

you can't connect to a destructor. Since your widget is a dialog connect it to the close() slot and additionaly to the deleteLater() slot or set the "widget attribute":http://qt-project.org/doc/qt-4.8/qwidget.html#setAttribute: to Qt::WA_DeleteOnClose to let Qt delete the dialog for you.

jastmc

Sorry, that was an older version, somehow. Thanks for your patience!
With this code, the button is ignored and has no effect.

What I meant to post was:-

@#include "mita_screen.h"
#include "ui_mita_screen.h"
#include <QtGui>
#include <QLabel>

mita_screen::mita_screen(QWidget *parent) :
QDialog(parent),
ui(new Ui::mita_screen)
{
mita_screen::setWindowFlags(Qt::SplashScreen);
ui->setupUi(this);

mita_state = 0;     // Initialise the state machine

QTimer *timer = new QTimer(this);
connect(timer, SIGNAL(timeout()), this, SLOT(state_update()));
timer->start(1000);

connect(ui->pushButton, SIGNAL(on_pushButton_clicked()), this, SLOT(mita_screen::close() ));
connect(ui->pushButton, SIGNAL(on_pushButton_clicked()), this, SLOT(mita_screen::deleteLater() ));

}

mita_screen::~mita_screen()
{
delete ui;
}

void mita_screen::state_update()
{
static int counter=0;

ui->label->setText(QString("%1").arg(++mita_state));

}

void mita_screen::on_pushButton_clicked()
{

}

void mita_screen::on_pushButton_pressed()
{

}
@

sierdzio

In your connect statement:

Not:
@
SLOT(mita_screen::close())
@

Instead:
@
SLOT(close())
@

SGaist

on_pushButton_clicked is a slot.

Try this:
@
connect(ui->pushButton, SIGNAL(clicked()), SLOT(close()));
@

Have a look at the "signal/slot":http://qt-project.org/doc/qt-4.8/signalsandslots.html and the "designer":http://qt-project.org/doc/qt-4.8/designer-manual.html documentation to have a better understanding of how it works