QScrollBar subControlRect ignores orientation Qt5.9.1

[Oleg21]

Hi everyone!

I recently started using Qt. Everything was fine, but once I worked with QScrollBar.
I needed to find out the coordinates of the Sub Controls.
For example, to find out the QStyle :: SC_ScrollBarSubLine coordinates and dimensions, I used the following code:

QStyleOptionSlider *opt = new QStyleOptionSlider;
opt->initFrom(scrollBar1);
 
QRect r = scrollBar1->style()->subControlRect(QStyle::CC_ScrollBar, opt, QStyle::SC_ScrollBarSubLine);

This code works great with a horizontal scrollbar.
Because with a vertical scrollbar, it is not possible to get coordinates and dimensions QStyle :: SC_ScrollBarSubLine.
More precisely, sizes and coordinates can be obtained,
but they will be equal to the size and coordinates of the QStyle :: SC_ScrollBarSubLine horizontal scroll bar.

Take a look at the pictures. They graphically show what I'm trying to find out.

Maybe some of you already encountered similar problems. Tell me how to solve them?


[SGaist]

Hi and welcome to devnet,

Can you post a minimal compilable sample that shows that ?

[Oleg21]

@SGaist

So of course, here is the program code:
scrollbar_test.h

#ifndef SCROLLBAR_TEST_H
#define SCROLLBAR_TEST_H

#include <QMainWindow>

class scrollbar_test : public QMainWindow
{
    Q_OBJECT

public:
    scrollbar_test(QWidget *parent = 0);
    ~scrollbar_test();
};

#endif // SCROLLBAR_TEST_H

scrollbar_test.cpp

#include "scrollbar_test.h"
#include <QtWidgets>
#include <QDebug>
#include <QStyle>
#include <QStyleOptionSlider>

scrollbar_test::scrollbar_test(QWidget *parent) : QMainWindow(parent)
{
    QScrollBar *scrollBar1 = new QScrollBar;
    scrollBar1->setParent(this);
    scrollBar1->setGeometry(QRect(10, 10, 100, 200));
    scrollBar1->setMinimum(0);
    scrollBar1->setMaximum(5);
    scrollBar1->setPageStep(5);
    /* When the horizontal position of the scroll bar works correctly */
    //scrollBar1->setOrientation(Qt::Horizontal);

    /* When the vertical position of the scroll bar does not work correctly */
    scrollBar1->setOrientation(Qt::Vertical);

    QStyleOptionSlider *opt = new QStyleOptionSlider;
    opt->initFrom(scrollBar1);

    QRect r = scrollBar1->style()->subControlRect(QStyle::CC_ScrollBar, opt, QStyle::SC_ScrollBarSubLine);

    /* In both cases, the variable r contains the same value, but should not be so */
    qDebug() << r;
}

scrollbar_test::~scrollbar_test()
{

}

[SGaist]

You are running that on Windows, right ?

[Oleg21]

@SGaist
Yes, I work in windows 7. Can this affect the result?
I tried to run this program under Windows XP. The result is the same.

[Oleg21]

@SGaist
Hi SGaist. I was able to solve the problem.
The reason is not in QScrollBar.
The reason was in QStyleOptionSlider.
In the code after these lines:

QStyleOptionSlider *opt = new QStyleOptionSlider;
opt->initFrom(scrollBar1);

I inserted the following code:

opt->orientation = Qt::Vertical;

And everything works.
Probably the reason is the incorrect transfer of parameters to the opt variable.

Thanks for the help, the issue is resolved.

[SGaist]

Great !

Thanks for sharing your findings !

One last thing, you are leaking your opt object. You should rather build it on the stack and pass its address to subControlRect.