Qt Embedded Linux - QWSKeyboardHandler

[zuck]

Hi!

We're using a biometric sensor as input device for an embedded project.

I've created a QWSKeyboardHandler derived class which sends some key press events to the QWSServer instance. It uses the QWSKeyboardHandler::processKeyEvent method to send all key press events.

pkFingerPrintManager::pkFingerPrintManager()
        : QWSKeyboardHandler()
{
    QWSServer::setKeyboardHandler(this);
}
 
// ... CUT ...
 
void pkFingerPrintManager::notifyInputEvent(int dx, int dy, int state)
{
    if (this->isNavigateRunning())
    {
        m_dx += dx;
        m_dy += dy;
 
        if (m_dx >= PK_FPM_KEY_THRESHOLD)
        {
            this->processKeyEvent(QEvent::KeyPress, Qt::Key_Right, 0, true, false);
            m_dx = 0;
        }
 
        if (m_dx <= -PK_FPM_KEY_THRESHOLD)
        {
            this->processKeyEvent(QEvent::KeyPress, Qt::Key_Left, 0, true, false);
            m_dx = 0;
        }
 
        if (m_dy >= PK_FPM_KEY_THRESHOLD)
        {
            this->processKeyEvent(QEvent::KeyPress, Qt::Key_Down, 0, true, false);
            m_dy = 0;
        }
 
        if (m_dy <= -PK_FPM_KEY_THRESHOLD)
        {
            this->processKeyEvent(QEvent::KeyPress, Qt::Key_Up, 0, true, false);
            m_dy = 0;
        }
 
        if (dx == 0)
            m_dx = 0;
 
        if (dy == 0)
            m_dy = 0;
    }
}

pkFingerPrintManager::pkFingerPrintManager()
        : QWSKeyboardHandler()
{
    QWSServer::setKeyboardHandler(this);
}

// ... CUT ...

void pkFingerPrintManager::notifyInputEvent(int dx, int dy, int state)
{
    if (this->isNavigateRunning())
    {
        m_dx += dx;
        m_dy += dy;

        if (m_dx >= PK_FPM_KEY_THRESHOLD)
        {
            this->processKeyEvent(QEvent::KeyPress, Qt::Key_Right, 0, true, false);
            m_dx = 0;
        }

        if (m_dx <= -PK_FPM_KEY_THRESHOLD)
        {
            this->processKeyEvent(QEvent::KeyPress, Qt::Key_Left, 0, true, false);
            m_dx = 0;
        }

        if (m_dy >= PK_FPM_KEY_THRESHOLD)
        {
            this->processKeyEvent(QEvent::KeyPress, Qt::Key_Down, 0, true, false);
            m_dy = 0;
        }

        if (m_dy <= -PK_FPM_KEY_THRESHOLD)
        {
            this->processKeyEvent(QEvent::KeyPress, Qt::Key_Up, 0, true, false);
            m_dy = 0;
        }

        if (dx == 0)
            m_dx = 0;

        if (dy == 0)
            m_dy = 0;
    }
}

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On my test machine (Linux x86) everything works.

Now we are testing it on the final ARM-based architecture but no key event is sent (or received). The process flow enters in one of the four "if" statements but the test widget doesn't receive any events.

This is the test widget "keyPressEvent" filter body:

void TestWidget::keyPressEvent(QKeyEvent* event)
{
    if (event->key() == Qt::Key_Left)
    {
        // ...
 
        event->accept();
 
        return;
    }
 
    if (event->key() == Qt::Key_Right)
    {
        // ...
 
        event->accept();
 
        return;
    }
 
    // ...
 
    event->ignore();
}

void TestWidget::keyPressEvent(QKeyEvent* event)
{
    if (event->key() == Qt::Key_Left)
    {
        // ...

        event->accept();

        return;
    }

    if (event->key() == Qt::Key_Right)
    {
        // ...

        event->accept();

        return;
    }

    // ...

    event->ignore();
}

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Could you help me to find the problem, please?

[wysota]

Maybe the problem is not in the keyboard handler? Are you sure your widget has keyboard focus? You could try applying an event filter on the application object and see if the events are delivered to the application at all.

[zuck]

I'm using "grabKeyboard" method to connect all key events to its parent widget. On my x86 machine it works.

[zuck]

I've added these lines to my QApplication (server) instance:

class MyKeyboardFilter : public KeyboardFilter
{
public:
    bool filter(int unicode, int keycode, int modifiers, bool isPress, bool autoRepeat)
    {
        qDebug() << unicode << keycode << isPress;
 
        return false;
    }
}
 
// ... CUT ...
 
qwsServer->addKeyboardFilter(new MyKeyboardFilter());
qwsServer->sendKeyEvent(QEvent::KeyPress, Qt::Key_Up, 0, true, false);

class MyKeyboardFilter : public KeyboardFilter
{
public:
    bool filter(int unicode, int keycode, int modifiers, bool isPress, bool autoRepeat)
    {
        qDebug() << unicode << keycode << isPress;

        return false;
    }
}

// ... CUT ...

qwsServer->addKeyboardFilter(new MyKeyboardFilter());
qwsServer->sendKeyEvent(QEvent::KeyPress, Qt::Key_Up, 0, true, false);

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but the "filter" method is never called

[wysota]

Did you do what I suggested?

[zuck]

Yes, as I've already said, I've created a keyoboard event filter in the QWSServer instance but it's never invoked...

[wysota]

That's not what I told you to do... And I see you didn't even read the docs of a method you used:

Note that the filter is not invoked for keys generated by virtual keyboard drivers (i.e., events sent using the sendKeyEvent() function).

I told you to install an event filter on the application object and not to set a keyboard filter on the server object.

[zuck]

You're right, I'm sorry.

Well, I've added an event filter to my QApplication instance:

class KeyPressEater : public QObject
{
    Q_OBJECT
 
public:
    KeyPressEater() : QObject(0) {};
    virtual ~KeyPressEater() {}; 
 
protected:
    bool eventFilter(QObject *obj, QEvent *event);
};
 
bool KeyPressEater::eventFilter(QObject *obj, QEvent *event)
{
    qDebug() << event->type();
 
    if (event->type() == QEvent::KeyPress) {
 
        QKeyEvent *keyEvent = static_cast<QKeyEvent *>(event);
        qDebug("Key press %d", keyEvent->key());
        return false;
 
    } else {
 
        // standard event processing
        return QObject::eventFilter(obj, event);
    }
}
 
// In QApplication code:
this->installEventFilter(new KeyPressEater());

class KeyPressEater : public QObject
{
    Q_OBJECT

public:
    KeyPressEater() : QObject(0) {};
    virtual ~KeyPressEater() {}; 

protected:
    bool eventFilter(QObject *obj, QEvent *event);
};

bool KeyPressEater::eventFilter(QObject *obj, QEvent *event)
{
    qDebug() << event->type();

    if (event->type() == QEvent::KeyPress) {

        QKeyEvent *keyEvent = static_cast<QKeyEvent *>(event);
        qDebug("Key press %d", keyEvent->key());
        return false;

    } else {

        // standard event processing
        return QObject::eventFilter(obj, event);
    }
}

// In QApplication code:
this->installEventFilter(new KeyPressEater());

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No key press event is received by my QApplication object.

[wysota]

On both x86 and ARM?

[zuck]

No, on the x86 platform all key events are correctly received and printed by the qDebug statement.

[wysota]

The first argument of processKeyEvent() is wrong. It should contain the unicode value of the key, not QEvent::KeyPress. Also make sure if the constructor of your subclass is called at all.

[zuck]

The first argument of processKeyEvent() is wrong. It should contain the unicode value of the key, not QEvent::KeyPress...

I'm a bit confused Why I need to specify both unicode and key code?

[wysota]

Don't ask me. I'm just looking at the API.