Lost on resizing QListWidget :(

idlefrog

How to get this QListWidget to resize to fit the contents?
Here's my code:

#include <QApplication>
#include <QListWidget>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QListWidget w;
    QStringList items = {"One", "Two", "Three"};
    w.addItems(items);
    w.adjustSize();

    w.show();
    return a.exec();
}

Which shows:

This window needs to be the same size as the containing text, like this:

Or, when there's longer items, something like this:

I did think adjustSize() was all that I required.
What command is required to adjust the size to the contents (horizontally)?

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:

jsulm

@idlefrog said in Lost on resizing QListWidget :(:

w.adjustSize();

Try to call this after w.show()

JonB

@jsulm
I have a question on this, which I have never understood fully in Qt widgets. Instead of having to call adjustSize() on showing/resizing/whatever (and btw here, is it necessary to call adjustSize() in the show/resize event, not just after w.show() which only sets a flag for show), is it not possible to set a size policy which would make Qt do this for you automatically? Or, is this not possible because it's a QListWidget?

idlefrog

@jsulm
Adding w.adjustSize() after w.show() has no effect. It looks exactly the same.

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!). :)