Widgets not visible in QGridLayout

[kshegunov]

Hello,
I've been struggling with a problem for a couple of days now and I'm pretty much at a loss. Here's the relevant code:

void RbDisplayGridLayout::put(const RbGraphWidgetList & list)
{
    layout()->addWidget(new QLabel("test"));  //< Widget shows
    for (int i = 0; i < list.size(); i++)
        layout()->addWidget(list[i]); //< Widget doesn't show
}

The list is defined as:

typedef QVector<RbGraphWidget *> RbGraphWidgetList;

and the RbGraphWidget is just a dummy defined with:

RbGraphWidget::RbGraphWidget(const Graph & meta, QWidget *parent)
    : QWidget(parent), graph(meta)
{
    ui.setupUi(this);

    setWindowTitle(graph.name);
    ui.label->setText(graph.name);
}

The ui.label is a simple QLabel that shows a string, nothing fancy here.

The odd thing is that I can see the dummy widgets just fine if I add them to a QTabWidget, but they don't display when I add them to the QGridLayout.
Did I miss something obvious?

[SGaist]

Hi,

That looks correct...

Some silly tests:

• add one of your custom widget the same way you do with your QLabel before the loop.
• create the list of your custom widget in the same method you pass them to your grid layout.

Are these widget used elsewhere ?

What version of Qt are you running ?
On what OS ?

[mrjj]

@kshegunov said in Widgets not visible in QGridLayout:

RbDisplayGridLayout

Is that a subclass of QGridLayout ?

[kshegunov]

@SGaist said in Widgets not visible in QGridLayout:

Hi,

Hi. I solved it, but I'm going to add answers to the questions just for posterity.

That looks correct...

It turns out it is correct.

Some silly tests:

• add one of your custom widget the same way you do with your QLabel before the loop.

Same result. The first thing I tried.

• create the list of your custom widget in the same method you pass them to your grid layout.

Hadn't tested that, but if I had, then I'd have had less gray hair. Your spidey sense is correct.

Are these widget used elsewhere ?

Yes, they're taken out from a QTabWidget as this:

RbGraphWidgetList RbDisplayTabLayout::take()
{
    int size = count();

    RbGraphWidgetList list;
    list.reserve(size);

    for (int i = 0; i < size; i++)
        list.append(reinterpret_cast<RbGraphWidget *>(widget(i)));

    QTabWidget::clear();

    // We need a clean slate before reinserting the widgets into another layout
    for (QWidget * widget : list)
        widget->setParent(nullptr);

    return list;
}

What version of Qt are you running ?

Qt 5.14.x

On what OS ?

Linux (debian testing), but I imagine the windows is going to behave the same.

---

Now what the problem was and how it is solved:

The problem is that (all) the widgets I get are hidden even the active one (probably by QTabWidget::clear). Calling show on them when I add them to the layout fixes the problem. Why is that isn't exactly clear to me, but it appears to be some idiosyncrasy of the tab widget I was not aware of, nor is it spelled in the docs explicitly.

---

EDIT:

@mrjj said in Widgets not visible in QGridLayout:

@kshegunov said in Widgets not visible in QGridLayout:

RbDisplayGridLayout

Is that a subclass of QGridLayout ?

No, it's a widget.

[mrjj]

So basically they were just hidden ?

[kshegunov]

@mrjj said in Widgets not visible in QGridLayout:

So basically they were just hidden ?

Yes, very much so.

[SGaist]

Intriguing behaviour !

I thought about suggesting adding a show call but forgot to add it 😅

Nice catch !