Zooming/Scrolling issue with QWheel Event

Saviz

Hello everyone,

I am currently trying to implement a zooming effect for my central QTextEdit by using QWheel event. However, I am facing an issue.

When I try to zoom in/out, the zoom effect works as expected. But when I use the mouse wheel, the scroll bar is being invoked as well, causing the QTextEdit to scroll up and down. I don't want this to happen as I want the position to remain the same and only to zoom in/out.

Code of MainWindow.cpp:

void MainWindow::wheelEvent(QWheelEvent *event)
{
    bool controlKeyIsHeld = QGuiApplication::keyboardModifiers().testFlag(Qt::ControlModifier);

    // If vertical mouse wheel goes up, then zoom in.
    if(event->angleDelta().y() > 0 && controlKeyIsHeld)
    {
        ui->QTextEdit_TextEdit->zoomIn(1);
    }

    else if(event->angleDelta().y() < 0 && controlKeyIsHeld)
    {
        ui->QTextEdit_TextEdit->zoomOut(1);
    }
}

Here is the virtual method in MainWindow.h:

protected:
    void wheelEvent(QWheelEvent *event) override;

jsulm

@Saviz You should subclass QTextEdit and override wheelEvent there instead of doing it in MainWindow.

Saviz

@jsulm Thank you so much. Your solution works perfectly.

Here is the code if anyone is interested:

QTextEditSubClass.h:

#ifndef QTEXTEDITSUBCLASS_H
#define QTEXTEDITSUBCLASS_H

#include <QTextEdit>

class QTextEditSubClass : public QTextEdit
{
    Q_OBJECT

public:
    explicit QTextEditSubClass(QWidget *parent = 0);
    ~QTextEditSubClass();

    // QWidget interface
protected:
    void wheelEvent(QWheelEvent *event) override;
};

#endif // QTEXTEDITSUBCLASS_H

QTextEditSubClass.cpp:

#include "qtexteditsubclass.h"
#include "qapplication.h"
#include "qevent.h"

QTextEditSubClass::QTextEditSubClass(QWidget *parent)
{

}

QTextEditSubClass::~QTextEditSubClass()
{

}

void QTextEditSubClass::wheelEvent(QWheelEvent *event)
{
    bool controlKeyIsHeld = QGuiApplication::keyboardModifiers().testFlag(Qt::ControlModifier);

    // If vertical mouse wheel goes up, then zoom in.
    if(event->angleDelta().y() > 0 && controlKeyIsHeld)
    {
        this->zoomIn(1);
        return;
    }

    else if(event->angleDelta().y() < 0 && controlKeyIsHeld)
    {
        this->zoomOut(1);
        return;
    }

    QTextEdit::wheelEvent(event);
}

After creating this sub class, we simply create a new instance of this class and pass it to the mainwindow central widget.

Hope this helps.

Musshca

Thank buddy for your searching ! But could you please share how do you implement in mainwindow?

I am using a qtextedit in my mainwindow where I want to zoom and when I implement by creating an instance of this class i am getting errors.

Thank you.