Preferences / Effect widgets: use '---' placeholder instead of 'None'

[ronso0]

... because in the Sound I/O tabs and in skins' effect regions --- is much easier to spot/recognize than None.

https://bugs.launchpad.net/mixxx/+bug/1892048

[daschuer]

Some first comments. This needs some brief tests if it effects the stored user data.

[ronso0]

I implemented your proposals and rebased (small commits, easy to review).
User data is not touched anymore, just the display strings in Preferences and the effect widgets.

[Holzhaus]

Thanks. I noticed an issue with the effect selector, but that may be unrelated to this branch:

[ronso0]

Thanks. I noticed an issue with the effect selector, but that may be unrelated to this branch:

That's unrelated.
Actually I only noticed it on Windows until now, because on Linux the menu is drawn over the effect selector (and positioned differently in general it seems).
Didn't yet find a pseudo state to style this...

[ronso0]

still ready..

[uklotzde]

Please remove the redundant string literals from comments. Instead describe the purpose of the code without repeating parts of the implementation in comments.

[ronso0]

Done @uklotzde

[uklotzde]

Ping @daschuer

[daschuer]

Works good now. Only one minor comment.

[Holzhaus]

I'm getting this debug assertion on shutdown:

DEBUG ASSERT: "!"Controls were leaked!"" in function void MixxxMainWindow::finalize() at /home/jan/Projects/mixxx/src/mixxx.cpp:870

However, this seems to be a bug in the 2.3 branch, not yours :(

LGTM, thank you.

[Be-ing]

I don't like this change. This feels like a regression. What was ever the problem with "None"? What was the motivation for changing this? Have you done any usability tests comparing this with "None"? I cannot recall any problems ever caused by the string "None". Who would know what --- means in this context? This looks bizarre IMO.

[ronso0]

... because in the Sound I/O tabs and in skins' effect regions --- is much easier to spot/recognize than None.

https://bugs.launchpad.net/mixxx/+bug/1892048

[daschuer]

I support the --- idea. It is much more recognizable especially if you also consider internationalisation.
And even in English there is the idiom "to dash something out"