Qt6.9: Mixer does not load on startup if visible

[krasko78]

Issue type

UX/Interaction bug (incorrect behaviour)

Description with steps to reproduce

Steps:

1. Make sure you are using Qt 6.9.
2. Start MuseScore with the Mixer open. Does not matter whether it is docked or floating.
   Actual: The Mixer appears empty with only the vertical separators visible.

Additional Info:
Further more, the height is smaller than the full height. This could be a consequence of the Mixer not loading.
Also, if you increase the height manually, you will see a partial "Audio FX" text and nothing else.
Finally, closing and re-opening the panel loads it properly.

Screenshot (with the height manually increased by me):

Supporting files, videos and screenshots

See above.

What is the latest version of MuseScore Studio where this issue is present?

Master with Qt6.9.

Regression

No.

Operating system

Windows 10

Additional context

No response

Checklist

• This report follows the guidelines for reporting bugs and issues
• I have verified that this issue has not been logged before, by searching the issue tracker for similar issues
• I have attached all requested files and information to this report
• I have attempted to identify the root problem as concisely as possible, and have used minimal reproducible examples where possible

[krasko78]

For some reason on the sectionContentList ListView in MixerPanelSection.qml, contentItem.childrenRect.height and contentItem.childrenRect.width are 0 when the MixerPanel is loaded the first time together with MuseScore. They are non-zero if the MixerPanel is closed and re-opened.

[cbjeukendrup]

Ah! That reminds me of #24326. The same change from that PR should be applied in the Mixer.

[krasko78]

Indeed the fix in PR 24326 fixes this issue. PR-ed.