[PyQt] Trouble with parenting in loaded .ui... but only on first load?

[Kyle Altendorf]

On 2018-12-28 11:50, Kyle Altendorf wrote:
> https://gist.github.com/altendky/b49af568393c2a4c597cdfbcbdfd5bdb
> 
> When loading the bad.ui which has a QStackedWidget holding the
> QTabWidget. Subsequent loads in the same process seem ok. The issue
> directly observed in my original code was that .findChildren() was
> unable to find the nvview.NvView widget. Here we can see that the
> QTabWidget isn't getting it's parent set to the QStackedWidget. I am
> assuming the QStackedWidget with the QTabWidget as the parent (in both
> bad and good cases) is an expected internal piece of the QTabWidget
> implementation.
> 
> The good.ui does not have the QStackedWidget and seems to load fine 
> regardless.
> 
> I tested this for each version on pypi back to 5.8 and they all seem
> to act the same. I have had code 'like' this (I deleted 99% or
> whatever to get down to this sscce) for a long time and it's been
> fine. I'm not sure why I started running into this only recently when
> I tried to add another tab.

https://gist.github.com/altendky/983344eb45776b94395cf460713b92ce

I got some help in #pyqt digging into this.  I added some debugging to 
uiparser.py and noticed that on the first load for bad, there were two 
reports of `UI version is 4.0` in the logging.  bad.ui uses the custom 
widget which loads fileview.ui so that makes sense.  But once uic comes 
out of the inner load, the outer load starts messing up.  It seems that 
the types have been changed around and so the `isinstance(item, 
QtWidgets.QWidget)` in `WidgetStack.popWidget()` starts failing.  You 
can look at the identifiers in the log but even the repr's have been 
totally changed.  So despite there  certainly being things that uic 
wants to match in that loop, they don't match.

One work around is to manually import the fileview module ahead of time 
so it's already parsed.  This makes sense with why it works after 
subsequent loads of the .ui as well.

Cheers,
-kyle