Manage widget focus

Agricola

I'm working on a C++ GUI. I use two QDial objects to control linear and angular velocity of a robot. Now I want to change the one Dial with up- and down-key, the other one with left- and right-key. How can I achieve that without having to use tab or mouseclicks to change the focus? I've tried to work with this function

void MainWindow::keyPressEvent(QKeyEvent *event)
{
    if(event->key() == Qt::Key_Up)
    {
        dial1->setFocus();
    }
    else if(event->key() == Qt::Key_Down)
    {
        dial1->setFocus();
    }
    else if(event->key() == Qt::Key_Left)
    {
         dial2->setFocus();
    }
    else if(event->key() == Qt::Key_Right)
    {
         dial2->setFocus();
    }
}

The Problem is, that the focus stays on the first widget focused. Do I have to set the focus back to the MainWindow after the keyboard input?
Can someone suggest a clever way to solve this issue?

Thanks a lot in advance!

raven-worx

@Agricola
The following code increases/decreases the dial values no matter where the current focus is (as long as the mainwindow of course is active). The events are consumed for up/down/left/right keys and thus are not delivered to the target widget.
Is this behavior what you want to achieve?

qApp->installEventFilter( myFilter );
...
bool MyFilter::eventFilter( QObject* watched, QEvent* event )
{
    switch( event->type() )
    {
        case QEvent::KeyPress:
        {
               QKeyEvent* ke = static_cast<QKeyEvent*>(event);
               switch( ke->key() )
               {
                      case Qt::Key_Up:
                             dial1->triggerAction( QAbstractSlider::SliderSingleStepAdd );
                             return true;
                      case Qt::Key_Down:
                             dial1->triggerAction( QAbstractSlider::SliderSingleStepSub );
                             return true;
                      case Qt::Key_Right:
                             dial2->triggerAction( QAbstractSlider::SliderSingleStepAdd );
                             return true;
                      case Qt::Key_Left:
                             dial2->triggerAction( QAbstractSlider::SliderSingleStepSub );
                             return true;
               }
        }
    }
    return ParentClass::eventFilter( watched, event );
}

(untested)

Agricola

@raven-worx
Thanks a lot for the suggestion! I used your input to do some research in the docs as well but I somehow have problems making it work. Maybe you can have a look on what I've done so far?!

I have added a new Class to my project that is derived from QObject and overrides the eventFilter()-Funktion.
keypressfilter.cpp:

#include "keypressfilter.h"

KeyPressFilter::KeyPressFilter(QObject *parent) : QObject(parent)
{

}

bool KeyPressFilter::eventFilter(QObject *obj, QEvent *event)
{
    switch(event->type())
    {
        case QEvent::KeyPress:
        {
            QKeyEvent* ke = static_cast<QKeyEvent*>(event);
            switch(ke->key())
            {
                case Qt::Key_Enter:
                    emit enterKeySig();
                    return true;
                case Qt::Key_Up:
                    emit upKeySig();
                    return true;
                case Qt::Key_Down:
                    emit downKeySig();
                    return true;
                case Qt::Key_Left:
                    emit leftKeySig();
                    return true;
                case Qt::Key_Right:
                    emit rightKeySig();
                    return true;
            }
        }
    }
    return QObject::eventFilter(obj, event);
}

I'm using Signals to make the changes to the dials in the MainWindow:
mainwindow.cpp (excerpt):

filter = new KeyPressFilter(this);
    connect(filter, SIGNAL(enterKeySig()), this, SLOT(enterKey()));
    connect(filter, SIGNAL(upKeySig()), this, SLOT(upKey()));
    connect(filter, SIGNAL(downKeySig()), this, SLOT(downKey()));
    connect(filter, SIGNAL(leftKeySig()), this, SLOT(leftKey()));
    connect(filter, SIGNAL(rightKeySig()), this, SLOT(rightKey()));

The Slots to trigger the Dial:

void MainWindow::upKey()
{
    Dial->triggerAction(QAbstractSlider::SliderSingleStepAdd);
}

This way it doesn't seem to work; the Signals are not emitted.
I've seen that it is possible to install the the filter in the App (that's what you did in your example as well right?), however I don't know how to convincingly call the Dials that way!?

raven-worx

@Agricola
are you calling qApp->installEventFilter()?
Also you are using the old connection style, which might fail at runtime - check the console output for errors.

Agricola

@raven-worx
Sorry if I wasn't specific enough. I solved the problem now; all I had to do was instantiating the filter and setting up the signal-slot-connections in the mainwindow.cpp and additionally (that's what I didn't grasp at first) calling

app.installEventFilter(win->filter);

in the main.cpp (win being the mainwindow object).

Thanks a lot for your help!