How to create a scrollable QVBoxLayout?

Question

I'm trying to put a QVBoxLayout inside a QScrollArea in order for it to be scrollable vertically. However items don't seem to be added to it.

I saw a suggestion that I ought to create an inner widget that the ScrollArea uses and to place the layout inside that, although it doesn't seem to have worked. My structure is supposed to look like this:

+-------------------------------
| QScrollArea(realmScroll)
| +----------------------------
| | QWidget(realmScrollInner)
| | +-------------------------
| | | QVBoxLayout(realmLayout)

And the code to do this:

# Irrelevant, added for context (this works)
centralWidget = QWidget(self)
self.container = QVBoxLayout(centralWidget)
centralWidget.setLayout(self.container)
self.setCentralWidget(centralWidget)

# Where trouble starts
self.realmScroll = QScrollArea(self.container.widget())
self.realmScroll.setVerticalScrollBarPolicy(Qt.ScrollBarAsNeeded)

self.realmLayout = QVBoxLayout(self.container.widget())

self.realmScrollInner = QWidget(self.realmScroll)
self.realmScrollInner.setLayout(self.realmLayout)

self.realmScroll.setWidget(self.realmScrollInner)
self.container.addWidget(self.realmScroll)

# Doesn't add to realmLayout
self.realmLayout.addWidget(QLabel("test"))

I'm still learning Qt (2 days in), so in-depth answers to where I'm going wrong would be appreciated.

Update:

It seems that the addWidget(QLabel()) works right up until the realmScrollInner has been set as realmScroll's widget. Since I'd like to add elements after the UI has been displayed I have to do this, which I'm not sure is really correct:

self.realmLayout.addWidget(QLabel("test"))

# realmScrollInner bound to realmScroll
realmScroll.setWidget(realmScrollInner)
self.container.addWidget(realmScroll)

# Access realmScroll's widget and then layout to add
realmScroll.widget().layout().addWidget(QLabel("test"))

But if you remove that first call to addWidget before the widget has been bound (so the layout has no widgets), then bind to the ScrollArea widgets added afterwards are not displayed. Perhaps the ScrollArea needs repainting (although I don't see a method for that)?

Update 2: Calling repaint() on realmScroll or its contained widget does nothing, as does calling activate/update() on the layout.

Answer 1

It turned out that I was lead down a wrong path by putting the layout as the layout of a widget. The actual way to do this is as simple as:

scrollarea = QScrollArea(parent.widget())
layout = QVBoxLayout(scrollarea)
realmScroll.setWidget(layout.widget())

layout.addWidget(QLabel("Test"))

Which I'm pretty sure I tried originally, but hey it's working.

However this adds an issue that the layout's items are shrunk vertically instead of causing the scrollarea to add a scrollbar.

Answer 2

OK, I just got done fighting with this. Here's a widget that can go into a scroll area (scrollarea->setWidget) and work correctly. It contains a QVBoxLayout and a list of label/listwidget pairs, each in their own little horizontal layout, and it does pretty much what you'd want.

The important thing was reading the QScrollArea docs section on Size Hints and Layouts, and finding the bit where having the sizeContraint QLayout::SetMinAndMaxSize on the layout would be necessary.

class MappingDisplayWidget : public QWidget
{
    Q_OBJECT
public:
    explicit MappingDisplayWidget(QWidget *parent = 0);
    void addFile(QString name);
private:
    QVBoxLayout *m_layout;
    QMap<QString, QListWidget *>  m_mappings;  
};


MappingDisplayWidget::MappingDisplayWidget(QWidget *parent) :
    QWidget(parent)
{
    m_layout = new QVBoxLayout;
    m_layout->setSizeConstraint(QLayout::SetMinAndMaxSize);
    setLayout(m_layout);
}


void MappingDisplayWidget::addFile(QString name) {
    if (m_mappings.find(name) == m_mappings.end()) {
        QWidget *widg = new QWidget;

        QHBoxLayout *lay = new QHBoxLayout;
        widg->setLayout(lay);

        QLabel *nlab = new QLabel(name);
        lay->addWidget(nlab);

        QListWidget *list = new QListWidget;
        lay->addWidget(list);

        m_layout->addWidget(widg);

        m_mappings[name] = list;
    }
}

I keep pointers to the list widgets so that I can add stuff to them later, and that works fine.

Answer 3

Try calling

self.realmScroll.setWidgetResizable(True)