Question

I’ve got some problem with signal for a button in Qt 4.8.0. I am using vs 2010 with Qt Designer. I have created a button in Designer with playButton name. But after that I tried to connect clicked() signal (in vs) with my function from CRenderArea (to start a timer), but it seems that it doesn’t work (the function start() works when I put it in the constructor, so it’s not the problem of the code itself). The code is compiling, the program is executing, but after clicking a button – nothing happens (it should move a line).

I would be really thankful for some help, just started a fun with Qt.

The codes are here (I hope the number of files won’t scare you, these are the simplest codes ever 🙂 ):

main.cpp

#include "ts_simulator.h"
#include <QtGui/QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    TS_simulator w;
    w.show();
    return a.exec();
}

ts_simulator.cpp:

TS_simulator::TS_simulator(QWidget *parent, Qt::WFlags flags)
    : QMainWindow(parent, flags)
{
    p_map = new CRenderArea();
    ui.setupUi( this );
    p_map->setParent( ui.renderArea );

    // this doesn't work, why?
    connect( ui.playButton, SIGNAL( clicked() ), this, SLOT( p_map->start() ) );
}

CRenderArea.h

#pragma once

#include <QtGui>

class CRenderArea : public QWidget {
    Q_OBJECT // I think it's necessary?

    int x;
    QBasicTimer* timer;
public:
    CRenderArea();
public slots: // this is necessary too, right?
    void start();
private:
    void timerEvent( QTimerEvent* );
    void paintEvent( QPaintEvent* );
};

and CRenderArea.cpp:

#include "CRenderArea.h"

CRenderArea::CRenderArea() : x( 0 ) {
    setBackgroundRole( QPalette::Base );
    setMinimumSize( 591, 561 );
    setAutoFillBackground( true );
    timer = new QBasicTimer();

}

void CRenderArea::timerEvent( QTimerEvent* e ) {
    ++x;
    update();
}

void CRenderArea::paintEvent( QPaintEvent* p ) {
    QPainter painter(this);
    painter.setRenderHint(QPainter::Antialiasing);
    painter.setPen(Qt::darkGray);
    painter.drawLine(2+x/10, 8, 60, 300);
}

void CRenderArea::start() {
    timer->start( 0, this );
}

Greets.

Answer 1

The problem is here:

connect( ui.playButton, SIGNAL( clicked() ), this, SLOT( p_map->start() ) );

if p_map is the receiver of the signal, and it has Q_OBJECT, it should be written as:

connect( ui.playButton, SIGNAL( clicked() ), p_map, SLOT(start()) );