No gtk theme/style in preferences with Qt 5.8

[Daniel Schürmann]

The preferences window has no theme after upgrade to ubuntu Bionic from Xenial.
The buttons are rectangular with icons.
Looks a bit 80s, matching Shade :-) but not desired.

[Be (be.ing)]

I doubt this is Mixxx's problem because the preferences window just uses Qt's theme. This sounds like an OS configuration issue.

[Daniel Schürmann (daschuer)]

Maybe this is related to this bug:
https://bugs.launchpad.net/ubuntu/+source/qtbase-opensource-src/+bug/1695618

[Daniel Schürmann (daschuer)]

This workaround works for me:

sudo apt install qt5-style-plugins
echo "export QT_QPA_PLATFORMTHEME=gtk2" >> ~/.profile

I am not sure if ubuntu thinks every user should do this to have nice looking Qt5 apps.
I will ask.

[Be (be.ing)]

I don't know how Ubuntu should solve this problem, but it is not any application's responsibility to solve this system problem.

[Daniel Schürmann (daschuer)]

If we put set this to Invalid, no one will find it.
At least we have a workaround posted here.

How is this solved on Fedora?

[Daniel Schürmann (daschuer)]

This is the Ubuntu bug: https://bugs.launchpad.net/ubuntu/+source/qtbase-opensource-src/+bug/1695618

I think we need a solution.

[Be (be.ing)]

IMO this is another case where it wouldn't be appropriate to hack a fix to an upstream bug in downstream software.

[Swiftb0y (swiftb0y)]

Mixxx now uses GitHub for bug tracking. This bug has been migrated to:
https://github.com/mixxxdj/mixxx/issues/9416