keep the library focused when any deck controls or the overview are clicked

[ronso0]

trying to fix https://bugs.launchpad.net/mixxx/+bug/1259040
"Clicking on deck controls affects library keyboard focus"

I added 'setFocusPolicy(Qt::NoFocus);' to the setup slot of most interactive skin widgets, like it worked for the library Preview button in #2264 .
This allows to keep the library focused for keyboard interaction when any deck controls or the overview are clicked.

I didn't apply the fix to the effect selector or spinboxes because I don't overlook the consequences and IMO there's no point to keep the library focused when interacting with those widgets.

This is a quite naive attempt but it works for buttons, sliders, knobs ...
It's so simple that I just can't believe there are no side effects. What can could wrong?
Is there a better place to set the focus policy?
Can it safely be set in wbasewidget ?

New behaviour:

• click buttons, knobs, sliders, overview: library table/sidebar remains focused
• effect selector: library is re-focused when any effect wass selected
• beat size spinboxes accept focus as before

[daschuer]

Thank you this works like a charm, there is only a code style issue.

[daschuer]

this-> is redundant and should be removed.

[ronso0]

because this is a wpushbutton actually. label..
will look into this again and fix it

[ronso0]

I'm done.

For the sake of completeness it would be nice to disallow click focus in the scrolling waveforms, but I don't find the right spot to fix it there, also I don't really want to mess with the waveforms ;)

[Be-ing]

Doesn't this make everything aside from the library inaccessible to screen readers?

[ronso0]

AFAIK there wouldn't be a drawback for screenreaders.
Screenreaders are operated by keyboard using mostly Tab and arrow keys to focus UI elements and convert those elements' 'tags' (title, alt etc. in html) for use with text-to-speech engines or tangible braille devices.
In Mixxx Tab/arrow keys and modifiers can only be used to navigate the main menubar, the library and the sidebar - buttons, knobs, sliders, waveform etc. can't be focused this way, neither can they be toggled with spacebar or Alt-Return or whatever. Our keyboard mappings are supposed to fill that gap.
Beatsize spinboxes and the effect selectors CAN be focused by mouse but AFAICT there's no way to focus any of them specificly with keyboards.

just asked @DJ-Ray about this https://mixxx.zulipchat.com/#narrow/stream/109171-development/topic/Optimzation.20for.20blind.20users/near/178858554

[daschuer]

Oh, I just see the redudnat "this->" is still there. Please remove it and this is geady for merge.

[ronso0]

Done.

[daschuer]

LGTM, Thank you.