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!

[anda_skoa]

Does the FirstWindow instance have focus when you press a key?

Key events are delivered to the widget which has keyboard focus, see QApplication::focusWidget().

Cheers,
_

[8Observer8]

I clicked on the window with the name "First Window" and press the "Space" key. Nothing happened.

290.png

---

Added after 11 minutes:

You are right. I added the button on the window:

void FirstWindow::on_pushButton_clicked()
{
    qDebug() << focusWidget()->windowTitle();
}

void FirstWindow::on_pushButton_clicked()
{
    qDebug() << focusWidget()->windowTitle();
}

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Output:

""

I don't understand why.

[anda_skoa]

Window title is not really helpful.
Check the value of fodusWidget() vs. "this"

Cheers,
_

[budda]

not sure if this helps but
in your header file I thought event method classes were supposed to be:

protected:
 void keyPressEvent( QKeyEvent *event );
 
private:
 
public:

protected:
 void keyPressEvent( QKeyEvent *event );

private:
       
public:

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[wysota]

I clicked on the window with the name "First Window" and press the "Space" key. Nothing happened.

Did you set QWidget::focusPolicy for the widget appropriately? If widget has Qt::NoFocus then it won't accept focus and thus won't receive key events.

[8Observer8]

I wrote it the constructor "setFocusPolicy( Qt::StrongFocus );"

FirstWindow::FirstWindow(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::FirstWindow)
{
    ui->setupUi(this);
    setFocusPolicy( Qt::StrongFocus );
}

FirstWindow::FirstWindow(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::FirstWindow)
{
    ui->setupUi(this);
    setFocusPolicy( Qt::StrongFocus );
}

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I added on the window the button:

void FirstWindow::on_pushButton_clicked()
{
    if ( focusWidget() == this ) {
        qDebug() << "focusWidget() == this";
    } else {
        qDebug() << "focusWidget() != this";
    }
}

void FirstWindow::on_pushButton_clicked()
{
    if ( focusWidget() == this ) {
        qDebug() << "focusWidget() == this";
    } else {
        qDebug() << "focusWidget() != this";
    }
}

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Output:

focusWidget() != this

[wysota]

When you click the button, it is most likely that the button gets the focus. Set the button's focus policy to Qt::NoFocus and try again. Better yet reimplement focusInEvent() and focusOutEvent() for your widget and print debug statements there to see when it receives and loses focus.

[8Observer8]

Yes, I see! I added Qt::NoFocus for the button:

FirstWindow::FirstWindow(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::FirstWindow)
{
    ui->setupUi(this);
    setFocusPolicy( Qt::StrongFocus );
    ui->pushButton->setFocusPolicy( Qt::NoFocus );
}

FirstWindow::FirstWindow(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::FirstWindow)
{
    ui->setupUi(this);
    setFocusPolicy( Qt::StrongFocus );
    ui->pushButton->setFocusPolicy( Qt::NoFocus );
}

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I added focusInEvent() and focusOutEvent():

#include "FirstWindow.h"
#include "ui_FirstWindow.h"
#include "QDebug"
 
FirstWindow::FirstWindow(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::FirstWindow)
{
    ui->setupUi(this);
    setFocusPolicy( Qt::StrongFocus );
    ui->pushButton->setFocusPolicy( Qt::NoFocus );
}
 
FirstWindow::~FirstWindow()
{
    delete ui;
}
 
void FirstWindow::keyPressEvent( QKeyEvent *event )
{
    qDebug() << "FirstWindow: keyPressEvent";
}
 
void FirstWindow::focusInEvent( QFocusEvent *event )
{
    qDebug() << "FirstWindow: focusInEvent";
}
 
void FirstWindow::focusOutEvent( QFocusEvent *event )
{
    qDebug() << "FirstWindow: focusOutEvent";
}
 
void FirstWindow::on_pushButton_clicked()
{
    if ( focusWidget() == this ) {
        qDebug() << "focusWidget() == this";
    } else {
        qDebug() << "focusWidget() != this";
    }
}

#include "FirstWindow.h"
#include "ui_FirstWindow.h"
#include "QDebug"

FirstWindow::FirstWindow(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::FirstWindow)
{
    ui->setupUi(this);
    setFocusPolicy( Qt::StrongFocus );
    ui->pushButton->setFocusPolicy( Qt::NoFocus );
}

FirstWindow::~FirstWindow()
{
    delete ui;
}

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

void FirstWindow::focusInEvent( QFocusEvent *event )
{
    qDebug() << "FirstWindow: focusInEvent";
}

void FirstWindow::focusOutEvent( QFocusEvent *event )
{
    qDebug() << "FirstWindow: focusOutEvent";
}

void FirstWindow::on_pushButton_clicked()
{
    if ( focusWidget() == this ) {
        qDebug() << "focusWidget() == this";
    } else {
        qDebug() << "focusWidget() != this";
    }
}

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When I click on the button I see:

focusWidget() == this

I will write in the constructor this insruction "setFocusPolicy( Qt::StrongFocus );" for all my MDI subwidnows