How to set a custom style into the QScrollBar of a QScrollArea?

Cesar

I have created a custom QProxyStyle "ScrollBarStyle" and im setting it on the vertical scrollbar of a QScrollArea

but the functions drawControl / drawComplexControl never get called, i also tried using QCommonStyle, same problem.

What I'm missing?

class ScrollBarStyle : public QProxyStyle
{
public:
   void drawControl(ControlElement element, const QStyleOption *option,
                                    QPainter *painter, const QWidget *widget) const override
   {
      qDebug() << "element: " << element;

      if (element == CE_ScrollBarSlider)
      {
         const QStyleOptionSlider *slider = qstyleoption_cast<const QStyleOptionSlider *>(option);
         if (slider)
         {
         }
      }
      else
      {
         QProxyStyle::drawControl(element, option, painter, widget);
      }
   }



   void drawComplexControl(ComplexControl control, const QStyleOptionComplex* 
      option,  QPainter* painter, const QWidget* widget) const override
   {
      qDebug() << "control: " << control;

      if (control == CC_ScrollBar && option->state & State_Horizontal)
      {
         const QStyleOptionSlider* sliderOption = qstyleoption_cast<const QStyleOptionSlider*>(option);
         if (sliderOption)
         {
               QRect handleRect = subControlRect(control, option, SC_ScrollBarSlider, widget);
               painter->setBrush(Qt::red);
               painter->drawRect(handleRect);
               return;
         }
      }

      QProxyStyle::drawComplexControl(control, option, painter, widget);

   }
};


class ScrollArea : public QScrollArea
{
    Q_OBJECT
public:

    ScrollArea(QWidget* parent = 0) : QScrollArea(parent) 
    {
        //this->setStyle(new ScrollBarStyle);
        this->horizontalScrollBar()->setStyle(new ScrollBarStyle);
    }
}

JoeCFD

@Cesar said in How to set a custom style into the QScrollBar of a QScrollArea?:

void drawControl(ControlElement element, const QStyleOption *option,
QPainter *painter, const QWidget *widget) const

I guess override is missing.

   void drawControl(ControlElement element, const QStyleOption *option,
                                    QPainter *painter, const QWidget *widget) const override
{
}

      void drawComplexControl(ComplexControl control, const QStyleOptionComplex* 
      option,  QPainter* painter, const QWidget* widget) const override
{
}

Cesar

@JoeCFD I'm already overriding them, its because i copied the functions in the cpp directly into the post, ill edit the post.

CPPUIX

@Cesar I tried to replicate this on my end, I have a QMainWindow, and adding a ScrollArea to it did not work as you said, drawControl() did not get called.

But it did work when I set its Style in mainWindow.

TQScrollArea *area = new TQScrollArea(this);

area->setStyle(new ScrollBarStyle); //adding this line made it work

Does this work for you?

Cesar

@Abderrahmene_Rayene said in How to set a custom style into the QScrollBar of a QScrollArea?:

TQScrollArea *area = new TQScrollArea(this);

area->setStyle(new ScrollBarStyle); //adding this line made it work

I didnt understand, you applied the style in the QScrollArea? or in the QMainWIndow?

CPPUIX

@Cesar in QMainWindow

Cesar

@Abderrahmene_Rayene even adding it to the QMainWindow it isnt getting called, adding it as qApp->setStyle() only drawControl get called, but never CE_ScrollBarSlider

In this similar question someone mentioned to do exactly what i tried, reimplementing the drawComplexControl.

And in this question he mentioned about needing to reset Qt::WA_OpaquePaintEvent to get the style working, but i didn't understand what he mean which "reset".

CPPUIX

@Cesar this solution does not fix your problem. I think he meant setting its attribute to false

area->verticalScrollBar()->setAttribute(Qt::WA_OpaquePaintEvent,false);

And sorry I didn't realize that I set the style of the scrollArea not the scrollBar, and it doesn't work yeah.

CPPUIX

@Cesar I had an idea, what if the reason it's not getting called is because there is no scrollBar to draw, so I added this line in QMainWindow:

area->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOn);

and it worked, both functions got called, drawControl / drawComplexControl

Cesar

@Abderrahmene_Rayene i already had the flag ScrollBarAlwaysOn set on, and im testing with a QScrollArea that the QScrollBar is visible.

At my side its still not getting called, even applying the style on the QMainWindow / QScrollArea QScrollBar

CPPUIX

@Cesar Then there's something else you should mention, because it does call drawComplex on my end, after I replicated what you posted, and the ScrollBar is drawn red and without arrows.

This is how it looks like:

JonB

@Abderrahmene_Rayene
You don't put a debug inside the if (sliderOption) to tell us, but are you saying that

const QStyleOptionSlider* sliderOption = qstyleoption_cast<const QStyleOptionSlider*>(option);

is returning nullptr/so false for the if? You never get to fprintf(stderr,"innercomplex\n");?

CPPUIX

@JonB I have edited my reply, see if you can correct what's wrong or provide a clarification.

JonB

@Abderrahmene_Rayene said in How to set a custom style into the QScrollBar of a QScrollArea?:

if (control == CC_ScrollBar && option->state & State_Horizontal)

Where do you (or the OP) get option->state & State_Horizontal from? I see Qt::Orientation QStyleOptionSlider::orientation? Do not assume QStyle::State_Horizontal is what you need for a QScrollbar....

CPPUIX

@JonB OP is using this function:

[override virtual] void QProxyStyle::drawComplexControl(QStyle::ComplexControl control, const QStyleOptionComplex *option, QPainter *painter, const QWidget *widget = nullptr) const

which should get called to draw the scrollBar.

As for State_Horizontal, it didn't work for me because I was setting the style for the vertical scroll bar, my bad. It works fine with the horizontal scroll bar. So why shouldn't one use it for QScrollBar.

Sorry for the over-editing, I'm replying and testing simultaneously, I have included an image to display the outcome, it works fine, I can't replicate OP's problem.

Cesar

@Abderrahmene_Rayene im not sure if i understood what you did, could you post a reproducible example of the code you're using?

CPPUIX

@Cesar I had TQScrollArea and ScrollBarStyle in a separate header file, but I included them in the mainwindow header so that I don't post 3 files contents.

mainwindow.cpp:

#include "mainwindow.h"
#include "./ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);


    TQScrollArea *area = new TQScrollArea(this);
    QWidget *widget = new QWidget();
    widget->setGeometry(0,0,700,400);
    area->setWidget(widget);
    area->horizontalScrollBar()->setStyle(new ScrollBarStyle);
    area->setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOn);
    area->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOn);

    area->setGeometry(0,0,500,300);
}

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

mainwindow.h:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QWidget>
#include <QScrollArea>
#include <QObject>
#include <QWidget>
#include <QScrollBar>
#include <QDebug>
#include <QStyleOptionSlider>
#include <QPainter>
#include <QProxyStyle>

class ScrollBarStyle : public QProxyStyle
{
public:


    void drawControl(ControlElement element, const QStyleOption *option,
                     QPainter *painter, const QWidget *widget) const override
    {

        fprintf(stderr,"before\n");
        if (element == CE_ScrollBarSlider)
        {
            fprintf(stderr,"after\n");
            const QStyleOptionSlider *slider = qstyleoption_cast<const QStyleOptionSlider *>(option);
            if (slider)
            {
            }
        }
        else
        {
            QProxyStyle::drawControl(element, option, painter, widget);
        }
    }

    void drawComplexControl(ComplexControl control, const QStyleOptionComplex*
                                                        option,  QPainter* painter, const QWidget* widget) const override
    {
        fprintf(stderr,"beforecomplex\n");

        if (control == CC_ScrollBar && option->state & State_Horizontal)
        {
            fprintf(stderr,"aftercomplex\n");
            const QStyleOptionSlider* sliderOption = qstyleoption_cast<const QStyleOptionSlider*>(option);
            if (sliderOption)
            {
                fprintf(stderr,"innercomplex\n");
                QRect handleRect = subControlRect(control, option, SC_ScrollBarSlider, widget);
                painter->setBrush(Qt::red);
                painter->drawRect(handleRect);
                return;
            }
        }

        QProxyStyle::drawComplexControl(control, option, painter, widget);

    }
};

class TQScrollArea : public QScrollArea
{
    Q_OBJECT
public:

    TQScrollArea(QWidget* parent = 0) : QScrollArea(parent)
    {
        this->verticalScrollBar()->setStyle(new ScrollBarStyle);
    }
};

QT_BEGIN_NAMESPACE
namespace Ui { class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private:
    Ui::MainWindow *ui;

};
#endif // MAINWINDOW_H

mainc.cpp is just the regular autogenerated one, didn't touch it.

JonB

@Abderrahmene_Rayene said in How to set a custom style into the QScrollBar of a QScrollArea?:

As for State_Horizontal, it didn't work for me because I was setting the style for the vertical scroll bar, my bad. It works fine with the horizontal scroll bar. So why shouldn't one use it for QScrollBar.

At the time you were saying the condition was not being entered. I didn't say option->state & State_Horizontal would not work, I said to check assumption, since there isa specific QStyleOptionSlider::orientation == Qt::Horizontal for a slider style option.

CPPUIX

@JonB thanks, that's a useful tip.

CPPUIX

@Cesar Btw you said you're setting style for the vertical scroll bar, but your code is handling horizontal bar style.