QTableWidget separtion lines disappearing

[tuli]

Hi,

I have a perhaps somewhat unusual setup of a QTableWidget, where the tablewidget contains QLabels as cell-widgets, and those labels contain pixmaps to render something.
The problem: when I drag the columnsseparator to the left, the column separation line disappears.

I have created a simple example of the problem below. Just run it and play around with resizing the columns by dragging the header. Quickly the separation line will disappear. Screenshot:

h2wdjy5.png

code:

class mm : public QWidget
{
    Q_OBJECT
public:
    mm(QWidget* parent = nullptr) : QWidget(parent)
    {
        setFixedSize(500,500);
        table.setColumnCount(2);
        table.setRowCount(1);
        table.verticalHeader()->setStretchLastSection(true);
 
        table.setCellWidget(0, 0, l1 = new QLabel());
        table.setCellWidget(0, 1, l2 = new QLabel());
 
        auto l = new QHBoxLayout();
        l->addWidget(&table);
        setLayout(l);
    }
 
    QLabel *l1, *l2;
    QTableWidget table;
 
    void paintEvent(QPaintEvent* e) override
    {
        {
            QPixmap pm(l1->size());
            pm.fill(Qt::red);
            l1->setPixmap(pm);
        }
        {
            QPixmap pm(l2->size());
            pm.fill(Qt::black);
            l2->setPixmap(pm);
        }
    }
};

class mm : public QWidget
{
    Q_OBJECT
public:
    mm(QWidget* parent = nullptr) : QWidget(parent)
    {
        setFixedSize(500,500);
        table.setColumnCount(2);
        table.setRowCount(1);
        table.verticalHeader()->setStretchLastSection(true);

        table.setCellWidget(0, 0, l1 = new QLabel());
        table.setCellWidget(0, 1, l2 = new QLabel());

        auto l = new QHBoxLayout();
        l->addWidget(&table);
        setLayout(l);
    }

    QLabel *l1, *l2;
    QTableWidget table;

    void paintEvent(QPaintEvent* e) override
    {
        {
            QPixmap pm(l1->size());
            pm.fill(Qt::red);
            l1->setPixmap(pm);
        }
        {
            QPixmap pm(l2->size());
            pm.fill(Qt::black);
            l2->setPixmap(pm);
        }
    }
};

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Why does this happen and how can I ensure the lines are always drawn?

Happy Holidays!

[anda_skoa]

Not necessarily the cause but it is usually not a good idea to override the paintEvent() method of a container.
Especially when not calling the base implementation.

If your cells really only contain a single color, my suggestion would be to set the background of the respective QTableWidgetItem instead.
http://doc.qt.io/qt-5/qtablewidgetit...#setBackground

Cheers,
_

[tuli]

Unfortuantley the single colors were just for demonstration.

Thanks for the tip, but the paint-event-overriding is indeed no the cause here. Indeed the issue even occurs when I set the pixmaps only once.

class mm : public QWidget
{
 
 //..as above, but without overriding paintEvent()
 
    void init()
    {
        {
            QPixmap pm(l1->size());
            pm.fill(Qt::red);
            l1->setPixmap(pm);
        }
        {
            QPixmap pm(l2->size());
            pm.fill(Qt::black);
            l2->setPixmap(pm);
        }
    }
};
 
...
    mm m;
    m.show();
    m.init();
...

class mm : public QWidget
{

 //..as above, but without overriding paintEvent()

    void init()
    {
        {
            QPixmap pm(l1->size());
            pm.fill(Qt::red);
            l1->setPixmap(pm);
        }
        {
            QPixmap pm(l2->size());
            pm.fill(Qt::black);
            l2->setPixmap(pm);
        }
    }
};

...
    mm m;
    m.show();
    m.init();
...

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Do you think this might be a Qt bug?

[anda_skoa]

Even if the pixmap is more complex, it make still sense to avoid cell widgets.

Set the pixmal as each item's DecorationRole or go for a custom delegate.

Cheers,
_