change page of stackwidget with scrollarea

Chris Kawa

If I understand you correctly you want to use mouse wheel to change current stack widget page and reflect that on a scrollbar. Is that correct?

If that is the case then there are two things to do.

First connect scrollbar's valueChanged signal to the stack widget's setCurrentIndex slot. (I see you already did that)

Second - you need to forward stack widget's wheel events to the scrollbar (this is how scrollarea does it). This part can't be done from the designer. Install an event filter on the stack widget and check for WheelEvent. Alternatively you can subclass the stackwidget and implement wheelEvent(). In any case, when you get a wheel event forward it to the scrollbar using QCoreApplication::sendEvent() method.

saber

@Chris-Kawa
i understood the steps .but i not sure how i can get the wheel event to scrollbar.

Chris Kawa

Lets say you have a stacked widget named stackedWidget, a scrollbar named verticalScrollBar and they are both placed in a MainWindow class.

In MainWindow's constructor you install event filter:

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    ui->stackedWidget->installEventFilter(this); //this is the important line
}

Then you override the eventFilter() method of MainWindow:

bool MainWindow::eventFilter(QObject* obj, QEvent* evt)
{
    if (obj == ui->stackedWidget && evt->type() == QEvent::Wheel)
    {
        QWheelEvent* wheel_evt = static_cast<QWheelEvent*>(evt);
        if (wheel_evt->orientation() == Qt::Vertical)
        {
            QCoreApplication::sendEvent(ui->verticalScrollBar, wheel_evt);
            return true;
        }
    }

    return QMainWindow::eventFilter(obj, evt);
}

If you also have a horizontal scroll you can handle it similarly.

saber

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saber

This post is deleted!

saber

@Chris-Kawa thanks for the sovle.
i made some changes.
first i removed the signal and slot. instead of signal i added the code in the event filter.
second changed some value of verticalScrollBar in designer .
Now it is working .but there is a problem when i move the verticalScrollBar up.it took mouse click to change the stackwidget page.
any solve for that leg problem?

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QMouseEvent>
#include <QWheelEvent>

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

    ui->stackedWidget->installEventFilter(this); //this is the important line
}

MainWindow::~MainWindow()
{
    delete ui;
}
bool MainWindow::eventFilter(QObject* obj, QEvent* evt)
{
    if (obj == ui->stackedWidget && evt->type() == QEvent::Wheel)
    {
        QWheelEvent* wheel_evt = static_cast<QWheelEvent*>(evt);
        if (wheel_evt->orientation() == Qt::Vertical)
        {
            QCoreApplication::sendEvent(ui->verticalScrollBar, wheel_evt);
            return true;
        }
    }

    int s = ui->verticalScrollBar->value();

    ui->stackedWidget->setCurrentIndex(s);


    return QMainWindow::eventFilter(obj, evt);
}

here is the value of verticalScrollBar in designer .

Chris Kawa

The way you modified eventFilter is completely wrong. This eventFilter method is called not only for mouse wheel events but for any kind of events - paint, resize, mouse clicks, keyboard, focus and tons more. That's why I put those if statements. You shouldn't put that scrollbar code outside the ifs.

If you don't want to use the designer for the connection put it in the MainWindow's constructor:

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

    //you don't have to copy my comments too ;)
    ui->stackedWidget->installEventFilter(this);
    connect(ui->verticalScrollBar, &QScrollBar::valueChanged, ui->stackedWidget, &QStackedWidget::setCurrentIndex);
}

and remove that code you added to the event filter.

saber

@Chris-Kawa
thanks.
i will do it.
any idea why click is needed to show the changed page, if scrollbar goes from down to up.

Chris Kawa

It's not required with the solution I proposed so it has to be some problem specific to your code or changes you made in the designer. From your screenshots I see you have most of the properties modified (bold font) although they are set to their default values. You should reset them to default if you don't want to modify them (the red arrow that appears on the right when you click on a property).

Could you reproduce the issue on a small, clean project with just the stack widget and a scrollbar? Alternatively could you package your project and share it so we could take a look?

saber

@Chris-Kawa

i will try in a clean project.
yes.i could do it .it is an GPLv2 app.
but it huge in cpp ,ui etc.
i will be releasing it within this month .i will inform you.
thanks for the reply.

saber

@Chris-Kawa

here is the beta app for linux .name corebox.
here