QLineEdit: how to handle up and down arrows? - qt

Question

I have a console input in my Qt based application, it's a QLineEdit, all Ui is designed via QtDesigner. Is it any easy way way to handle up and down arrows in order to implement input history? The 'go to slot' only show returnProcessed signal, no way i can see to handle up and down arrows :(

Answer 1

you can install event filter and watch your line edit event in your window class. Below is an example:
declare event handler method on your window class:
class MainWindow : public QMainWindow {
Q_OBJECT
...
protected:
void changeEvent(QEvent *e);
...
};
window constructor
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
...
ui->lineEdit->installEventFilter(this);
}
event handler implementation:
bool MainWindow::eventFilter(QObject* obj, QEvent *event)
{
if (obj == ui->lineEdit)
{
if (event->type() == QEvent::KeyPress)
{
QKeyEvent* keyEvent = static_cast<QKeyEvent*>(event);
if (keyEvent->key() == Qt::Key_Up)
{
qDebug() << "lineEdit -> Qt::Key_Up";
return true;
}
else if(keyEvent->key() == Qt::Key_Down)
{
qDebug() << "lineEdit -> Qt::Key_Down";
return true;
}
}
return false;
}
return QMainWindow::eventFilter(obj, event);
}
hope this helps, regards

Answer 2

You can subclass QLineEdit and re-implement the virtual keyPressEvent method to handle your special keys.
void MyLineEdit::keyPressEvent(QKeyEvent *event)
{
if(event->key() == Qt::Key_Up){
// move back in history
}
else if(event->key() == Qt::Key_Down){
// move forward in history
}
else{
// default handler for event
QLineEdit::keyPressEvent(event);
}
}

Answer 3

I had the same problem, but I find out in other forums that you need to setFocus, e.g.:
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
...
ui->lineEdit->installEventFilter(this);
this->setFocus();
}
It works for me.
Reference:
http://www.qtforum.org/article/28240/how-to-get-arrow-keys.html

Answer 4

For me in PyQt this was not working,
class MainWidget(QtGui.QMainWindow):
def __init__(self):
QtGui.QMainWindow.__init__(self)
self.setupUi()
self->installEventFilter(self)
But this worked,
class MainWidget(QtGui.QMainWindow):
def __init__(self):
QtGui.QMainWindow.__init__(self)
self.setupUi()
QtGui.QApplication.instance().installEventFilter(self)