Qt Mouse Event on QLabel

A good example that help you learn how to handle mouse events

After settings we got a new class named MyQLabel, which inherits from QWidget.

myqlabel.h

myqlabel.cpp

And now we replace QWidget with QLabel, as shown below

myqlabel.h

myqlabel.cpp

The label indeeds inherits from MyQLabel now.

Go back to myqlabel.h

Threre are three override events in QLabel, including mouseMoveEvent, mousePressEvent

and mouseRelaseEvent.

mainwindow.h

create four connections between sender (ui->lblMouse) and their receivers declared in the mainwindow

========================================================================

myqlabel.h

#ifndef MYQLABEL_H

#define MYQLABEL_H

#include <QLABEL>

#include <QMouseEvent>

#include <QEvent>

#include <QDebug>

class MyQLabel : public QLabel

    Q_OBJECT

public:

    explicit MyQLabel(QWidget *parent = nullptr);

    void mouseMoveEvent(QMouseEvent *ev) override;

    void mousePressEvent(QMouseEvent *ev) override;

    void mouseReleaseEvent(QMouseEvent *ev) override;

    void leaveEvent(QEvent *);

    int x, y;

signals:

    void Mouse_Pressed();

    void Mouse_Release();

    void Mouse_Move();

    void Mouse_Left();

};

#endif // MYQLABEL_H

myqlabel.cpp

#include "myqlabel.h"

MyQLabel::MyQLabel(QWidget *parent) : QLabel(parent)

void MyQLabel::mouseMoveEvent(QMouseEvent *ev)

    // get current mouse position

    this->x = ev->x();

    this->y = ev->y();

    emit Mouse_Move();

    qDebug() << "signal:: mouseMoveEvent";

void MyQLabel::mousePressEvent(QMouseEvent *ev)

    emit Mouse_Pressed();

    qDebug() << "signal:: mousePressEvent";

void MyQLabel::mouseReleaseEvent(QMouseEvent *ev)

    emit Mouse_Release();

    qDebug() << "signal:: mouseReleaseEvent";

void MyQLabel::leaveEvent(QEvent *)

    emit Mouse_Left();

    qDebug() << "signal::leaveEvent";

mainwindow.h

#ifndef MAINWINDOW_H

#define MAINWINDOW_H

#include <QMainWindow>

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;

public slots:

    // receive singals emitted by a MyQLabel instance

    void Mouse_Pressed();

    void Mouse_Relese();

    void Mouse_Move();

    void Mouse_Left();

};

#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"

#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)

    : QMainWindow(parent)

    , ui(new Ui::MainWindow)

    ui->setupUi(this);

    connect(ui->lblMouse, SIGNAL(Mouse_Move()), this, SLOT(Mouse_Move()));

    connect(ui->lblMouse, SIGNAL(Mouse_Pressed()), this, SLOT(Mouse_Pressed()));

    connect(ui->lblMouse, SIGNAL(Mouse_Release()), this, SLOT(Mouse_Relese()));

    connect(ui->lblMouse, SIGNAL(Mouse_Left()), this, SLOT(Mouse_Left()));

MainWindow::~MainWindow()

    delete ui;

void MainWindow::Mouse_Pressed()

    ui->lblMouse_Current_Event->setText("Mouse Pressed!");

    qDebug() << "ui slot:: Mouse Pressed!";

void MainWindow::Mouse_Relese()

    ui->lblMouse_Current_Event->setText("Mouse Released!");

    qDebug() << "ui slot:: Mouse Released!";

void MainWindow::Mouse_Move()

     ui->lbl_Mouse_Current_Pos->setText(QString("X = %1, Y = %2").arg(ui->lblMouse->x).arg(ui->lblMouse->y));

     ui->lblMouse_Current_Event->setText("Mouse Moving!");

void MainWindow::Mouse_Left()

    ui->lblMouse_Current_Event->setText("Mouse Left!");

     qDebug() << "ui slot:: Mouse Left!";

References:

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