CODEWITHSUNDEEP
c++qt
Shan-Hung Hsu
Shan-Hung Hsu

Reputation: 137

(Qt) Qtimer doesn't work. What details have I missed?

I wrote a header xx.h, there are two classes, one is a Qt class "QClass" and another is a generic class "Normal". And declare an external Normal variable. Normal has a QClass member.
Here is the content of xx.h :

#ifndef XX_H
#define XX_H

#include <QObject>
#include <QTimer>

class QClass : public QObject
{
    Q_OBJECT

public:
    QClass();
    ~QClass();

private:
    QTimer *t;
private slots:
    void func();
};

class Normal
{
    int i;

    QClass q;
};

extern Normal globalN;

#endif

I also wrote a xx.cpp to implement xx.h

#include "xx.h"

QClass::QClass() : t(new QTimer)
{
    connect(t, SIGNAL(timeout()), this, SLOT(func()));
    t->start(1000);
}

QClass::~QClass()
{
    delete t;
}


void QClass::func()
{
    static int n = 0;
    ++n;
}

And here is my main.cpp, here I define globalN. The class Why is my Qt window class, it is declared in why.h. This header is not important, so I didn't post its content.

#include "why.h"
#include "xx.h"
#include <QtWidgets/QApplication>

Normal globalN;

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

My idea is that I put globalN in global scope, so when program starts, it constructs globalN, then the timer start to tick.
In order to check these stuff work right or not, I set a breakpoint in QClass::func(), to check if QTimer calls func(), but it doesn't.
I examine the code a long time, but I can't find where I mistake, please tell me. Thank you!!

Upvotes: 2

Views: 1048

Answers (1)

dydil
dydil

Reputation: 997

For your timer to start, you need an event loop. To have an event loop you need to have an active QApplication.

Here, since globalN is global, it is created before your QApplication, so your timer is not started.

Upvotes: 9

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