Expanding QListView within QScrollArea

infoctopus

maleadt,

could you upload a .deb file and/or your project that contains minimal code for reproducing the issue. I could run it on my n900

maleadt

Sure, here are all the files (haven't got the Maemo SDK at hand right now):

main.cpp
@#include <QApplication>
#include "testcase.h"

int main(int argc, char **argv)
{
QApplication tApplication(argc, argv);
Testcase tWidget;
tWidget.show();
tApplication.exec();
}@

testcase.h
@#include <QMainWindow>
#include <QListView>
#include <QStandardItem>
#include <QLabel>
#include <QStandardItemModel>

class Testcase : public QMainWindow
{
Q_OBJECT
public:
Testcase()
{
// View
QListView* tView = new QListView();
setCentralWidget(tView);
tView->setEditTriggers(QAbstractItemView::NoEditTriggers);
tView->setSelectionBehavior(QAbstractItemView::SelectRows);
tView->setSelectionMode(QAbstractItemView::SingleSelection);

    // Model
    QStandardItemModel *tModel = new QStandardItemModel(0, 1);
    tView->setModel(tModel);
    populateModel(tModel, tView);
}

private:
void populateModel(QStandardItemModel iModel, QListView iView)
{
// Add a regular text item
QStandardItem *tItem = new QStandardItem("Item containing text");
iModel->appendRow(tItem);

    // Add a regular widget
    QLabel *tLabelRegular = new QLabel("Item containing a label");
    iModel->appendRow(new QStandardItem());
    iView->setIndexWidget(iModel->index(1, 0), tLabelRegular);
     
    // Add an expanding widget (using a size policy)
    QLabel *tLabelExpanding = new QLabel("Item containing a label with expanding size policy");
    tLabelExpanding->setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Expanding);
    iModel->appendRow(new QStandardItem());
    iView->setIndexWidget(iModel->index(2, 0), tLabelExpanding);
     
    // Add an expanding widget (using an enforced size)
    QLabel *tLabelExpandingForcibly = new QLabel("Item containing a label with enforced minimum height");
    iModel->appendRow(new QStandardItem());
    tLabelExpandingForcibly->setMinimumHeight(100);
    iView->setIndexWidget(iModel->index(3, 0), tLabelExpandingForcibly);
}

};@

testcase.pro
@QT += core gui
SOURCES += main.cpp
HEADERS += testcase.h@

Displays the same erroneous behaviour on desktop Qt.

goetz

The size policy is only taken into account for Layouts (QLayout and subclasses), but not for widgets in item views.

maleadt

I see. But then the obvious question is: how do I make a widget within an item view consume all available space, without manually doing that?

goetz

As far as I know, this is not possible.

You might consider to drop the list view and only use widgets and a layout, if that's possible with the logic you want to implement.

maleadt

Sadly, I really need the QListView functionality, so I cannot revert completely to a QWidget-based layout. But the part which is troubling me right now (a simple label to display there are no results), will only be visible when no QListView functionality is needed.

So I tried to add the widget which unsuccessfully expands within the listview to the main layout. But now the QListView is working against me as well: it won't compress to its minimal required size :(

See this image:
!http://imgur.com/PeJq9.png(QListView fails to compress.)!

The label displaying "No history or favourites" is configured with a MinimumExpanding vertical policy, while the listview has a "Minimum" vertical policy in place. Both are added to a QVBoxLayout.

But the size policies don't matter at all... The listview only contains a single item, being the two buttons visible at top of the window. Yet the sizeHint of the QListView returns a whopping 192 px, which is WAY to much for what its worth.
How come the QListView returns a sizeHint which doesn't match the amount of items actually present in the listview?

Thanks for bearing with me, I'm still quite new with Qt :)

goetz

I have similar use cases in my applications. In that case I use a "QStackedWidget":http://doc.qt.nokia.com/latest/qstackedwidget.html. On page is a QLabel with expanding/expanding size policy that displays the "nothing to show" hint, the other is the list view. Maybe that would be of help for you too?

maleadt

Thanks for mentioning that! For some screens that widget will come in very handy, but I won't be able to use it for all of them. The example above requires two buttons to be scrollable all the time, so they need to be part of the QListView. Hence, the QListView needs to be visible all the time as well, therefore I cannot use the QStackedWidget.

I however have found a workaround to fix the layout compression issue. When the "No history or favourites" widget is visible, I configure the listview to have a fixed size equal to the sum of all sizeHints of the containing items (only the button header, in this case). When however the QListView actually contains items, I configure the size to be the sizehint of the QListView itself.

Not nice, as the QListView should really manage itself (or I don't get a certain aspect of QListView item management), but it at least doesn't rely on hard-coded pixel constants like the other workarounds I tried during the last days :)

goetz

"Not nice" is relative - if it works for you, the solution is at least a good workaround. Sometimes on has to do these nasty tricks...

maleadt

I know that. I just like to keep as close to the intended semantics as possible, because that quite often improves maintainability a lot. But hey, I'm happy I got it working, and maybe one day I'll find a proper solution :) Thanks for the help!