How to catch enter key

En Ar Bg De El Es Fa Fi Fr Hi Hu It Ja Kn Ko Ms Nl Pl Pt Ru Sq Th Tr Uk Zh

There are many different situations where you can use the enter key, e.g. to start a search action. But implementing something like this is not that easy - Qt catches enter keys before you even get the event.

Solution

Fortunately, Qt allows to reimplement the general event catching method. You need a new class with a method like this:

bool eventFilter(QObject* obj, QEvent* event);

That's everything:

class keyEnterReceiver : public QObject
{
    Q_OBJECT
protected:
    bool eventFilter(QObject* obj, QEvent* event);
};

Now, we have to implement the method:

bool keyEnterReceiver::eventFilter(QObject* obj, QEvent* event)
{
    if (event->type()==QEvent::KeyPress) {
        QKeyEvent* key = static_cast<QKeyEvent*>(event);
        if ( (key->key()==Qt::Key_Enter) || (key->key()==Qt::Key_Return) ) {
            //Enter or return was pressed
        } else {
            return QObject::eventFilter(obj, event);
        }
        return true;
    } else {
        return QObject::eventFilter(obj, event);
    }
    return false;
}

That was quiet fast - so here is a detailled explanation:

Key pressed?

First, we check if any key was pressed. If not, it is a event that has nothing to do with keys - and Qt should handle it:

bool keyEnterReceiver::eventFilter(QObject* obj, QEvent* event)
{
    if(event->type()==QEvent::KeyPress) {
        …
    } else {
        return QObject::eventFilter(obj, event);
    }
    return false;
}

Convertion

We got a QEvent as a parameter. To read out which key was pressed, we need to convert the QEvent to a QKeyEvent:

QKeyEvent* key = static_cast<QKeyEvent*>(event);

Enter/Return or another key?

That's it. Now we only have to check whether it was "our" enter key or another key we are not interested in:

if ( (key->key()==Qt::Key_Enter) || (key->key()==Qt::Key_Return) ) {
    //Enter or return was pressed
} else {
    return QObject::eventFilter(obj, event);
}
return true;

Finally, we can install our event handler: keyEnterReceiver* key = new keyEnterReceiver(); aWidgetInAnotherClass->installEventFilter(key);