keyPressEvent doesn't work

[8Observer8]

Hi

This is my steps:

- I created the "Qt Widget Application"
- I opened the "MainWindow.ui" file and put on it the "mdiArea"
- I created the "Qt Designer Form Class" and wrote in the "MainWindow.h" and "MainWindow.cpp" files:

private:
    Ui::MainWindow *ui;
    FirstWindow *m_firstWindow;
    SecondWindow *m_secondWindow;
    ThirdWindow *m_thirdWindow;

private:
    Ui::MainWindow *ui;
    FirstWindow *m_firstWindow;
    SecondWindow *m_secondWindow;
    ThirdWindow *m_thirdWindow;

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MainWindow.cpp

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
 
    m_firstWindow = new FirstWindow;
    m_secondWindow = new SecondWindow;
    m_thirdWindow = new ThirdWindow;
 
    QMdiSubWindow *w1 = ui->mdiArea->addSubWindow( m_firstWindow );
    ui->mdiArea->addSubWindow( m_secondWindow );
    ui->mdiArea->addSubWindow( m_thirdWindow );
 
    ui->mdiArea->cascadeSubWindows();
 
    w1->resize( 500, 500 );
}

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

    m_firstWindow = new FirstWindow;
    m_secondWindow = new SecondWindow;
    m_thirdWindow = new ThirdWindow;

    QMdiSubWindow *w1 = ui->mdiArea->addSubWindow( m_firstWindow );
    ui->mdiArea->addSubWindow( m_secondWindow );
    ui->mdiArea->addSubWindow( m_thirdWindow );

    ui->mdiArea->cascadeSubWindows();

    w1->resize( 500, 500 );
}

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- I opened "FirstWindow.h" and "FirstWindow.cpp" files and wrote:
FirstWindow.h

private:
    Ui::FirstWindow *ui;
    void keyPressEvent( QKeyEvent *event );
};

private:
    Ui::FirstWindow *ui;
    void keyPressEvent( QKeyEvent *event );
};

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FirstWindow.cpp

void FirstWindow::keyPressEvent(QKeyEvent *event)
{
    qDebug() << "keyPressEvent";
}

void FirstWindow::keyPressEvent(QKeyEvent *event)
{
    qDebug() << "keyPressEvent";
}

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- I ran the application and pressed on the keys. But I didn't see the text "keyPressEvent" on the "Application Output"

Thank you!