[Building/Packaging] Build issue with Qt 5 with QList initializer

[sebojolais]

Describe the problem
Since this commit , this line:

https://github.com/OpenBoard-org/OpenBoard/blame/310eabe20a2838472a73e751d60b8d3e6f46d85e/src/gui/UBThumbnailScene.cpp#L36

mThumbnailItems{document->proxy()->pageCount()}

throws an error during the build with Qt5:

src/gui/UBThumbnailScene.cpp:36:7: error: no matching function for call to ‘QList<UBThumbnail*>::QList(<brace-enclosed initializer list>)’
   36 |     , mThumbnailItems{document->proxy()->pageCount()}
      |       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/x86_64-linux-gnu/qt5/QtCore/qobject.h:49,
                 from /usr/include/x86_64-linux-gnu/qt5/QtWidgets/qgraphicsscene.h:44,
                 from /usr/include/x86_64-linux-gnu/qt5/QtWidgets/QGraphicsScene:1,
                 from src/gui/UBThumbnailScene.h:26,
                 from src/gui/UBThumbnailScene.cpp:23:

Because the QList constructor of Qt 6 does not exist in Qt 5.

If OB does not support Qt 5 anymore, sorry for this false positive.

Versions
Provide version information for all components and libraries.

• OpenBoard version dev branch
• Qt version 5.15.6

[sebojolais]

A solution that works for both Qt5 and 6 should be:

UBThumbnailScene::UBThumbnailScene(UBDocument* document)
    : mDocument{document}
{
    mThumbnailItems.reserve(document->proxy()->pageCount());
}

[letsfindaway]

Thanks for pointing this out. Qt5.15 shall still be supported!

However reserve() is not what I want. It just allocates the memory. However I want that the entries are actually created and default initialized (which means nullptr for a list of pointers).

QList has no such function, not even resize(). So I now think the best idea would be to replace this with a QVector: In Qt5, the QVector has that constructor taking a size. In Qt6, QVector and QList are even synonyms. What do you think?

[sebojolais]

Thank you for your quick answer.
Yes QVector is fine.
I tested it in my side with success.

[letsfindaway]

Pushed a commit on my branch which is probably the next candidate for merging and which continues the rework of the thumbnails. See letsfindaway@4dffb67