Comment # 21 on bug 1149986 from Xu Zhao

After some research, I have finally fixed this problem completely.
This is because when the application starts up (step-1), it uses gtk2 theme
prior to the gtk3 theme (specified by qt5-base).
However, when later Telegram initializes the gtk environment (step-2), it
searches for the gtk3 library first, if found, use the gtk3 library. If not
found, use the gtk2 library.
When both gtk2 and gtk3 libraries co-exist in the system, the application will
first use gtk2 theme to start up (in step-1), then use gtk3 libraries to
initialize (in step-2), mix using two libraries causes a failed start.

To fix this, I have created a patch to let Telegram always favor gtk2 over gtk3
during initialization, since openSUSE has chosen to enable gtk2 theme by
default in qt5-base.

Please help test my patch at:
https://build.opensuse.org/package/show/home:nuklly:branches:server:messaging/telegram-desktop
on XFCE, Cinnamon, GNOME, etc. The version works on KDE.

Note that I have to add the libappindicator1 as a hard dependency because
Telegram can only use gtk2 with libappindicator1 for notification.

(In reply to Marcel Kuehlhorn from comment #19)
> Created attachment 819630 [details]
> Fallback theme
> 
> > A quick question: which Cinnamon package hard depends on libqt5-qtstyleplugins-platformtheme-gtk2?
> 
> > ~> zypper se --requires libqt5-qtstyleplugins-platformtheme-gtk2
> > S | Name                        | Summary                                      | Type   
> > --+-----------------------------+----------------------------------------------+--------
> >   | cinnamon-session            | The session manager for the Cinnamon Desktop | package
> >   | libqt5-qtstyleplugins-devel | Qt 5 Style Plugins Development Files         | package
> >   | mate-session-manager        | MATE Session Manager                         | package
> 
> > Also, what do you mean by "QT apps on GTK falling back to the GNOME default
> > theme"? My understanding of setting GTK3 as the first will result in QT apps
> > on GTK3 falling back to GTK3 theme, which is correct behavior.
> 
> If you look at this Screenshot, you notice that Keepass falls back to the
> default theme instead of using the GTK3 version of the set theme