[Interest] QCombobox - resize list view to horizontal contents

[Daniel Price]

I have a Qt-Windows applicastion.

I have a non-editable QComboBox subclass with a custom QAbstractListModel driving it. I have a simple QListView subclass acting as the view for the combobox.

I need the list view (NOT the combo) to resize horizontally to fit the widest string in the list instead of being fixed to the width of the combo button.

Previously, I used a QListWidget subclass as a the view and overrode the sizeHint():

struct ComboListWidget : public QListWidget
{
                ComboListWidget(QWidget *parent = 0)
                :
                                QListWidget(parent)
                {}

                virtual QSize sizeHint() const
                {
                                QFontMetrics fm(font());

                                int maxWidth = 0;
                                for (int i=0; i < count(); ++i)
                                {
                                                QListWidgetItem *it = item(i);
                                                const QSize sz = fm.size(Qt::TextSingleLine, it->text());
                                                maxWidth = qMin(qMax(maxWidth, sz.width()), MaxListWidth);
                                }

                                QMargins mar = contentsMargins();
                                int hpad = (mar.left() + mar.right()) * 2;

                                return QSize(maxWidth + hpad, 0);
                }
};

But this code was really expensive, particularly if the list contains dozens of entries.

As I'm now using a custom model, I tried to implement a custom SizeHintRole:

if (role == Qt::SizeHintRole)
{
                const QString &text = data(index, Qt::DisplayRole).value<QString>();

                QFontMetrics fontMetrics(data(index, Qt::FontRole).value<QFont>());
                //QSize size(fontMetrics.width(text), fontMetrics.height());
                return QSize(1000,20); // ignores the 1000
                //return size;
}

But the list view only uses the vertical size and I nothing I do seems to work. If I set the list view to a fixed width in it's constructor, it breaks the selection-highlight such that it only extends as far as the combobox's width.

This only seems to be a problem on Windows. On OSX, the list view expands correctly with no additional code.

There must be a way to do this - please help!

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