App cannot be started on clean Trusty desktop

Interestingly weather, calendar and reminders are the three that are unaffected.

I notice that weather has a export QT_SELECT=qt5 prior to calling qmlscene, whereas music-app does not.
#!/bin/bash
export QT_SELECT=qt5
qmlscene /usr/share/ubuntu-weather-app/ubuntu-weather-app.qml
pat@pat-samsung:~$ more /usr/bin/music-app
#!/bin/bash
qmlscene /usr/share/music-app/music-app.qml
They both work properly on my system, but mine is not quite a clean install, and perhaps installing the SDK effects this.
Other compiled apps like reminders not invoked with qmlscene will work as well

Ok, setting QT_SELECT=qt5 with all of the apps and it works, so I'll create a merge request for them all.

Actually that's not going to fix the problem. The desktop file doesn't call the script to start the app. If we change /usr/bin/music-app we'll fix it for the people running music app from that script, but not from the dash or any other icon.

qt5-default wasn't installed on my clean trusty VM. Installing it "fixed" the issue.

It's complex, so trying to explain the situation is:
- We've QT_SELECT=qt5 set globally on the device, that's why everything works there without setting anything
- 'qt5-default' depends on development files, so it can't be used by default
- qmlscene is considered 'development binary' by upstream and 'not recommended for production', and while there has been talk that we need a simple replacement for it (since what it does is relatively simple too), those plans haven't went forward AFAIK
- The reason you see 'qt4' mentioned is because that's nowadays the fallback option when there is no configuration selected, which helps eg. KDE to remain functioning similar to before

So this is the same issue as what was on device, happening on desktop. Luckily, the qtchooser offers many ways of setting the Qt version - configuration, env var, program parameter.

You should try:
'qmlscene -qt5 /usr/share/music-app/music-app.qml' for the desktop file?

The other poorer solutions include:
- Call '/usr/lib/*/qt5/bin/qmlscene' - if expansion works, that'll also works
- A more exact version of above, call '/usr/lib/$(dpkg-architecture -qDEB_HOST_MULTIARCH)/qt5/bin/qmlscene'
- Set QT_SELECT=qt5 before launching

Bonus:
- Upstream has provided a new 'qml' binary supposed to be more suitable for those uses people have used 'qmlscene' for, so you may want to experiment with 'qml -qt5 /usr/share/music-app/music-app.qml' (after apt-get install qml). It's still worth investigating at some point, since there could be eg. startup time improvement.

Ok, confirmed that adding "-qt5" to the qmlscene command line allows the apps to run on the desktop without having to install any additional packages. Thanks Timo.

So what is the solution to this? Do we recommend adding -qt5 to the qmlscene command in the .desktop file of all the core apps?

Yes Nekhelesh

Fix committed into lp:ubuntu-clock-app at revision 370, scheduled for release in ubuntu-clock-app, milestone 1.8

Fix committed into lp:sudoku-app at revision 166, scheduled for release in sudoku-app, milestone Unknown

Fix committed into lp:ubuntu-calculator-app at revision 230, scheduled for release in ubuntu-calculator-app, milestone 1.6

Fix committed into lp:music-app at revision 374, scheduled for release in music-app, milestone 1.0

Fix committed into lp:ubuntu-filemanager-app at revision 148, scheduled for release in ubuntu-filemanager-app, milestone alpha-1

stock ticker has the same issue, not listed as affected, will add

notes-app suffers from the same issue, adding -qt5 to the .desktop file exec entry works for the Unity8 / preview session

Fix committed into lp:ubuntu-terminal-app at revision 47, scheduled for release in ubuntu-terminal-app, milestone alpha-1

Fix committed into lp:stock-ticker-mobile-app at revision 72, scheduled for release in stock-ticker-mobile-app, milestone Unknown

This bug was fixed in the package notes-app - 1.4+14.04.20140415-0ubuntu1

---------------
notes-app (1.4+14.04.20140415-0ubuntu1) trusty; urgency=low

  [ Bill Filler ]
  * add -qt5 to fix desktop launching (LP: #1288885)
 -- Ubuntu daily release <email address hidden> Tue, 15 Apr 2014 16:43:16 +0000

Fix committed into lp:dropping-letters at revision 46, scheduled for release in dropping-letters, milestone Unknown