F : QWidget: Must construct a QApplication before a QWidget

rktech

Changed files from begining(note, running on android, on desktop it runs correctly):
Calculations.cpp

#include "calculations.h"

Calculations::Calculations()
{

}
int Calculations::Percent(int source, int percent){
    return source*percent/100;
}
void Calculations::row(QPushButton *p, QProgressBar *b){
QDesktopWidget dw;
p->setGeometry(Percent(dw.width(),75),Percent(dw.height(),c),Percent(dw.width(),25),Percent(dw.height(),4));
b->setGeometry(0,Percent(dw.height(),c),Percent(dw.width(),75),Percent(dw.height(),4));
c+=4;
return;
}

Calculations.h

#ifndef CALCULATIONS_H
#define CALCULATIONS_H
#include <QApplication>
#include <QPushButton>
#include <QProgressBar>
#include <QDesktopWidget>
class Calculations
{
public:
    Calculations();
    static int Percent(int source, int percent);
    void row(QPushButton *p, QProgressBar *b);
private:
    int c = 28;
   // QDesktopWidget dw;
};

#endif // CALCULATIONS_H

Christian Ehrlicher

@rktech said in F : QWidget: Must construct a QApplication before a QWidget:

QDesktopWidget dw;

Please read the documentation...: https://doc.qt.io/qt-5/qdesktopwidget.html#obtaining-a-desktop-widget

rktech

@Christian-Ehrlicher I have read it, but I can't figure how to do it better. I have only one screen on my phone. So how can I define the dw better?

mrjj

Hi

It's static so it must be initialized somewhere which is executed before main, yes.

Ok. Im asking as the instance is first created in MainWindow and i cannot
reproduce it here using a static in a class which first is instantiated after QApp in main.

Im well aware that global/ global static is initilized before main but i did not know also it goes for
statics inside class that is created later than QApp.

Live and lean, i guess :)

Christian Ehrlicher

@mrjj I meant the static in the header in the first post - I wondered if it really linked (I would guess no since the static dw was not initialized anywhere) therefore my guess is there is more than we see here.

rktech

@mrjj Anything that comes to me by this? I am sorry, I am a beginner.

mrjj

@rktech
Sorry no new ideas.

After you removed all use of static.
then clean the build folder (delete all files)
so we are sure its all recompiled.
Then rebuild all.

If you still get that warning then there must be a static or global var in some other file not shown.

Also using the code shown, i dont get this warning on desktop.

But you still get it on Android but not Desktop ?
And you are 100% sure it was totallt recompiled after you removed static ?

When you say "And removed static from QdesktopWidget dw in .cpp"
that was for the one inside a function, correct ?
Not something outside class or function ?

rktech

Cleaned, remaked and now it worked

Christian Ehrlicher

@rktech said in F : QWidget: Must construct a QApplication before a QWidget:

Cleaned, remaked and now it worked

Then please mark this topic as solved, thx.

mrjj

@rktech
Super. So it was the statics.
So i also learned something new :)