Keyboard Input in Qt

Qt Widget - how to capture just a few keyboard keys

Your own comment says it all:

return TRUE; // eat event

As you return true for all keys, the event won't be further processed. You must return false for all keys you don't want to handle.

Another way without event filter but reimplementing keyPressEvent:

void MyWidget::keyPressEvent( QKeyEvent* event ) {
    switch ( event->key() ) {
    case Qt::Key_X:
        //act on 'X'
        break;
    case Qt::Key_Y:
        //act on 'Y'
        break;
    default:
        event->ignore();
        break;
    }
}

QKeyPress - Simulating key press in Qt

In the link you indicate an enter is given so the text is not necessary, but in the case you want to send a letter you must pass that parameter:

ui->lineEdit->setFocus();
QKeyEvent *key_press = new QKeyEvent(QKeyEvent::KeyPress, Qt::Key_X, Qt::NoModifier, "X");
//                                                                          text ─────┘
QApplication::sendEvent(ui->lineEdit, key_press);

How to modify the keyboard input in QT?

Could this example be useful to you ?

They use a mecanism called completer, that provides different words for a given entry... It's quite like a dictionnary on a cell phone...

Custom Completer Example :

http://qt.nokia.com/doc/4.6/tools-customcompleter.html

Hope it helps a bit !

How can I intercept the pressing of multiply (*) key in my C++ Qt calculator app?

try using this case (Qt::Key_Asterisk):