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:
    bool eventFilter(QObject* obj, QEvent *e) override;
...
};

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