Question

I am trying to implement in Qt a main window which has 2 widgets: one area where I draw some points and one list box where I write all the points with their respective coordinates. And I would like to implement the function “delete point” of a button on the main window, i.e. when I press the button then the point selected from the list box should disappear from my area where I am drawing. So I was thinking of doing this with signals/slots, but when I try to gain access to my list of points from my drawing area it just doesn’t find any containing data. This is my code until now:

paintwidget.cpp (my main window):

PaintWidget::PaintWidget(QWidget parent) :
        QWidget(parent),
        ui(new Ui::PaintWidget)
{
    area = new RenderArea(this);
    ui->setupUi(this);
    connect(ui->displayWidget, SIGNAL(listUpdated(QList)), ui->pointsListWidget,
            SLOT(onListUpdated(QList*)));
    connect(ui->deletePoints, SIGNAL(clicked()), this, SLOT(deleteItem()));
}
void PaintWidget::deleteItem()
{
    area->deletePoint(ui->pointsListWidget->currentItem());
}

renderarea.cpp (my drawing area):

void RenderArea::mousePressEvent(QMouseEvent *e)
{
    point = e->pos();
    updateList(point);
    this->update();
}
void RenderArea::updateList(const QPoint& p)
{
    list.append(p);
    if (list.count()>1)
        lineAdded(p);
    emit listUpdated(&list);
}
void RenderArea::paintEvent(QPaintEvent * /* event */)
{
    QPainter painter(this);
    painter.setPen(QPen(Qt::black,2));
    for (int i = 0; i < list.size(); ++i)
        painter.drawPoint(list[i]);
    if (list.size()>1)
        for(int j = 0; j < list.size()-1; ++j)
            painter.drawLine(list[j], list[j+1]);
}
void RenderArea::deletePoint(QListWidgetItem *item)
{
    bool ok1;
    bool ok2;
    int index = item->text().indexOf(",");
    int x = item->text().left(index).toInt(&ok1, 10);
    int y = item->text().mid(index + 1).toInt(&ok2, 10);
    for (int i = 0; i < list.size(); ++i)
        //find the point with x and y as coordinates and delete it
}

listbox.cpp:

void ListBox::onListUpdated(QList *list)
{
    clear();
    for (int i = 0; i < list->size(); ++i)
        addItem(new QListWidgetItem(QString::number(list->at(i).x()) + ", " +
                                    QString::number(list->at(i).y())));
}

The list from the render area is a QList of QPoints. The problem is that in the FOR-loop the size of the list is 0 so I cannot see any of the points that it should contain. I think that I am failing to initialize it somewhere but I am not sure where.

The points are drawn with QPainter so when I delete the point from the list is there any possibility to delete them from my drawing area also?

Answer 1

I’m suspecting you’ve got two RenderArea widgets hanging around for some reason.

You’re connecting ui->displayWidget‘s signal, but acting on the area widget for the delete.

Shouldn’t you be calling ui->displayWidget->deletePoint or connecting area‘s signal?

As for the repaint, you should call the widget’s update() method to have it repaint itself.