[Interest] Support for Qt 5 & Qt 6 in QML app

[Ulf Hermann]

Hi,

> I need to migrate a Qt 5 application with QML ui to Qt 6 without
> losing Qt 5 support. What is the best approach here? Version-specific
> resources? File selectors (by the way is it even possible to select
> QML files based on the Qt version?) I mean it is clear that
> platform-specific code/imports needs to be wrapped into
> platform-specific components, but what is the best way to select the
> right component?

File selectors are generally not a great idea as we cannot know ahead of 
time what they will evaluate to at run time. What concrete problems are 
you facing? Most QML code written for Qt 5 should still work with Qt 6.

You can use qmldir imports to select between different modules based on 
Qt version. By constructing your qmldir files from the build system you 
can change what your module imports at compile time. Unfortunately we 
don't have a good API for defining QML modules in Qt5. The only thing we 
have there is CONFIG+=qmltypes in qmake. You need to write build system 
code that generates or copies the qmldir file into place.

qmldir imports have a number of quirks in Qt5. They pretty much only 
work when the import statement is in a qmldir file of a QML module that 
also defines some other types. The other types have to be implemented in 
C++ and there must not be any *.qml files in the same module. In Qt6, 
qmldir imports are less of a pain.

best regards,
Ulf