Mouse events form a critical component of GUI interaction in Qt applications. Mastering mouse event handling provides a foundation for understanding other event types, as their underlying principles are large consistent.

Custom Widget Implementation

A custom label class is created to demonstrate mouse event processing:

mylabel.h

#ifndef MYLABEL_H
#define MYLABEL_H

#include <QLabel>

class MyLabel : public QLabel
{
    Q_OBJECT
public:
    explicit MyLabel(QWidget *parent = nullptr);

protected:
    void enterEvent(QEvent *) override;
    void leaveEvent(QEvent *) override;
    void mousePressEvent(QMouseEvent *) override;
    void mouseReleaseEvent(QMouseEvent *) override;
    void mouseMoveEvent(QMouseEvent *) override;
};

#endif // MYLABEL_H

mylabel.cpp

#include "mylabel.h"
#include <QMouseEvent>

MyLabel::MyLabel(QWidget *parent) : QLabel(parent)
{
    setMouseTracking(true);
}

void MyLabel::enterEvent(QEvent *)
{
    setText("Do not touch me!");
}

void MyLabel::leaveEvent(QEvent *)
{
    setText("You finally left...");
}

void MyLabel::mousePressEvent(QMouseEvent *event)
{
    QString buttonName;
    switch (event->button()) {
    case Qt::LeftButton:
        buttonName = "Left Button";
        break;
    case Qt::RightButton:
        buttonName = "Right Button";
        break;
    default:
        buttonName = "Unknown";
        break;
    }

    QString message = QString("[%1] Pressed at (%2, %3)")
                      .arg(buttonName)
                      .arg(event->x())
                      .arg(event->y());

    setText(message);
}

void MyLabel::mouseReleaseEvent(QMouseEvent *event)
{
    QString buttonName;
    switch (event->button()) {
    case Qt::LeftButton:
        buttonName = "Left Button";
        break;
    case Qt::RightButton:
        buttonName = "Right Button";
        break;
    default:
        buttonName = "Unknown";
        break;
    }

    QString message = QString("[%1] Released at (%2, %3)")
                      .arg(buttonName)
                      .arg(event->x())
                      .arg(event->y());

    setText(message);
}

void MyLabel::mouseMoveEvent(QMouseEvent *event)
{
    QString buttonName;
    if (event->buttons() & Qt::LeftButton) {
        buttonName = "Left Button";
    } else if (event->buttons() & Qt::RightButton) {
        buttonName = "Right Button";
    } else {
        buttonName = "No Button";
    }

    QString message = QString("[%1] Moved to (%2, %3)")
                      .arg(buttonName)
                      .arg(event->x())
                      .arg(event->y());

    setText(message);
}

The implementation enables tracking of mouse movements, presses, and releases within the custom widget. Mouse tracking is enabled through setMouseTracking(true), which allows the widget to receive mouse move events even when no buttons are pressed.