Problem with EventFilter and QEvent::KeyRelease event

[davidesalvetti]

Hi all,

I'm having a problem using the eventfilter and the QEvent::KeyRelease event. In my desktop app I just want to know when a key from the keyboard has been released. Let's say I click the T key, I want to know when the key is released. this is my piece of code:

bool MainWindow::eventFilter(QObject *obj, QEvent *event)
{
    if (event->type() == QEvent::KeyPress)
    {
        QKeyEvent *keyEvent = static_cast<QKeyEvent *>(event);
//           qDebug() << "key " << keyEvent->key() << "from" << obj << "PRESSED";
           if(keyEvent->key() == Qt::Key_T)
           {
              t_pressed = true;
           }
    }
    else if(event->type() == QEvent::KeyRelease)
    {
        QKeyEvent *keyEvent = static_cast<QKeyEvent *>(event);
           qDebug() << "key " << keyEvent->key() << "from" << obj << " RELEASED";
           if(keyEvent->key() == Qt::Key_T)
           {
               t_pressed = false;
           }
    }
    else if(event->type() == QEvent::ShortcutOverride)
    {
        QKeyEvent *keyEvent = static_cast<QKeyEvent *>(event);
//        qDebug() << "key " << keyEvent->key() << "from" << obj << "OVERRIDE";
    }

    return QObject::eventFilter(obj, event);
}

Now if I keep the button pressed, let's say for 2 seconds, I continuously get the QEvent::KeyRelease although I didn't release the key. That's strange, but in this way I cannot get the QEvent::KeyRelease in the right way, because if I keep the button pressed I always get the QEvent::KeyRelease .

Am I missing something?
Thanks in advance!

[JonB]

@davidesalvetti
I am guessing from your description, assuming it is true/happens for you at least, is to do with auto-repeat when you hold a key down. Multiple key release events seems to be generated to signal up-level that the letter is auto-repeating. It may vary by person/platform, e.g. see https://stackoverflow.com/questions/48025384/qt-how-to-filter-keypressevent-with-autorepeat. The OP said it was happening to him, a respondent said he could not reproduce it, have a read.

Anyway, if that really is the case, you will have no choice but to change code so that: clearly the only way to recognise will be when you do not get another key release (of same key) within the short auto-repeat period. You'll have to set a one-shot timer for that, reset on each key release: when it times out, the previous key release was the final genuine release.

[davidesalvetti]

Thanks for your answer, I was looking for a cleaner way to do it but using a QTimer works fine for now.
Thanks again!