Lost on resizing QListWidget :(

[jsulm]

@JonB I think you're right. Calling show() does not yet show anything and so does not size the widgets.
@idlefrog Try to play with sizePolicy of your widget.

[idlefrog]

Here's my brute force solution:

#include <QApplication>
#include <QListWidget>
#include <QDebug>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QListWidget w;    
    QStringList items = {"CO2 - Carbon Dioxide", "H2O - Water", "NaCl - Sodium Choride", "NH3 - Ammonia" };
    w.addItems(items);

    auto column_width = w.sizeHintForColumn(0);
    auto widget_size = w.sizeHint();
    auto frame_width = w.frameWidth();
    auto margins = w.contentsMargins();
    auto new_width = column_width+frame_width + margins.left()+margins.right();
    
    widget_size.setWidth(new_width);
    w.resize(widget_size);

    w.show();

    return a.exec();
}

Which looks like this:

I'll try the size policy next :)

[idlefrog]

@jsulm
I've tried every size policy, but none make any useful difference.
It seems that QListWidget does not support an 'adjust to fit contents'.

There is a setSizeAdjustPolicy(QAbstractScrollArea::AdjustToContents), but that doesn't respect the size of the items in the list.

[JoeCFD]

This will do it.
QFont font = w->font(); /*get default font */
QRectF fontBoundRect = QFontMetrics( font ).tightBoundingRect( the longst string );
w->setFixedWidth( fontBoundRect.width() );
sure you may need some margins.

[idlefrog]

@JoeCFD said in Lost on resizing QListWidget :(:

QFont font = w->font(); /*get default font */
QRectF fontBoundRect = QFontMetrics( font ).tightBoundingRect( the longst string );
w->setFixedWidth( fontBoundRect.width() );

That works in the same way as my bruit force method, although I prefer to use:
auto column_width = w.sizeHintForColumn(0); as there is only one column.

For a simple list widget I would expect to see some 'fitToContents' behaviour.
Perhaps it is hidden somewhere, but I haven't uncovered it yet.

(Manually adjusting the size by calculating the contents/margins/frame every time I add/remove an item seems complicated for something that simple).

[JoeCFD]

@idlefrog Some basic operation. Better to know it. This applies for more scenarios. Often, some features do not exist while they are expected from Qt.

[idlefrog]

This is my final solution for anyone else out there wondering why their list will not 'fit to content':

#include <QApplication>
#include <QListWidget>
#include <QDebug>
#include "listwidget.h"

class ListWidget : public QListWidget
{
public:
    explicit ListWidget(QWidget *parent = nullptr):QListWidget(parent){}
    ~ListWidget(){}

    QSize sizeHint() const
    {
        QSize size = QListWidget::sizeHint();
        auto column_width = sizeHintForColumn(0);
        auto frame_width = frameWidth();
        auto margins = contentsMargins();
        auto new_width = column_width+frame_width + margins.left()+margins.right();
        size.setWidth(new_width);

        return size;
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    ListWidget w;
    QStringList items = {"C2H6O - Ethanol",
                         "CHCl - Trichloromethane",
                         "CO2 - Carbon Dioxide",
                         "H2O - Water",
                         "NaCl - Sodium Choride",
                         "NH3 - Ammonia"  };
    w.addItems(items);
    w.setSizePolicy(QSizePolicy::Preferred, QSizePolicy::Fixed);
    w.show();
    return a.exec();
}

Which looks like this:

[idlefrog]

@JoeCFD Thanks!... It's surprising really. Perhaps Widgets are not being developed now.

[JonB]

@idlefrog
Your solution uses sizeHintForColumn() and overrides sizeHint(). I believe this is indeed the correct approach, as per the accepted solution at QListWidget adjust size to content. However a couple of comments there claim not working at Qt 5.x, so good if it works for you.

[idlefrog]

@JonB Yes, it works fine for me on Qt 5.15.2. Thanks for the support!
And thanks for the link! (I had found that one too!). :)